NP... Deleted.... However... You should know that in the latter of those 65 Images...the importance of what happens whenever the Brake Pedal is stepped upon in relation to the TCC Activity in response may be integral to other aspects of things.
NEED HELP Intermittent PRDNL Indicator Weirdness, P0700 and other Goodness
- Thread starter spfautsch
- Start date
I appreciate your input here, but I didn't make it past the first 10 images. At the time I had bigger fish to fry. They're fried now, read on.
That's an interesting tangent I've thought about but not in great detail. That input is a +12v signal, so if it's shorting to another power source that could be worth investigating. If it's broken / going open or shorting to ground it shouldn't make any difference. Also, it doesn't really explain why the previous TCM module eventually failed completely, setting persistent RAM verification errors. Or, why this problem seems to be directly related to temperature.
Edit: To further clarify, the previous TCM dying seems to a me a sign that whatever is happening is causing the TCM's voltage regulator / power supply filtering to be overtaxed, causing "dirty" power to the processor and memory of the TCM and subsequently causing the processor to reboot due to low voltage.
Almost ready to test. If this doesn't work it'll make good nesting material for all the birds living in my back yard.
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Well... Since I'm Batting a Thousand so far with NOT rendering any useful information to this Thread... I'll give this once last try...
Check Out @MAY03LT 's contribution shown in Post # 2 via THIS Link:
gmtnation.com
But from hereon out... it will be a "Mokusatsu" situation... 黙 殺
Check Out @MAY03LT 's contribution shown in Post # 2 via THIS Link:
The 5 Transmission p codes
I seen the video on this subject from GMTnation, I cannot find anything on it here to help me I am new to the site. I have the five P0740 p0753 p0758 p0785 p1860. I tested fuse 47 it has power both sides. I swapped an ignition switch from my 02 envoy that I had smashed up. Reset codes and...
gmtnation.com
But from hereon out... it will be a "Mokusatsu" situation... 黙 殺
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Appreciated, but already have page 164 and 166 of the 2006 Ranier 'WIRING.PDF' service manual printed in color, cut and taped together, in duplicate. It's what's in the background underneath the break-out cable and has every circuit connected to the TCM.
Edit: One thing the diagram you referenced got me thinking about - it, and most of the other references including the 2006 Ranier PDF collection - incorrectly depict the D2 switch in the manifold pressure switch (most trans guys refer to this as the "pillow switch"). It is in fact a normally closed switch, which when D2 applies breaks the circuit grounding the D4 / D3 normally open switches. I got some white-out and fixed my printed copies so as not to chase ghosts should I get to looking at this one.
Got Rusty out of storage this morning and have the break-out cable and the newest TCM module in place. Starts and runs with no issues. That's as far as I got b/c I threw my back out pulling weeds this morning and after mowing my lawn that's about as far as I'm able to get.
Have a Hantek CC65 clamp-on current sensor on the way that should make visualizing solenoid currents much easier. Just need to find my BNC extension cable so I can feed it through the firewall along with some home-made test clip leads.
Edit: One thing the diagram you referenced got me thinking about - it, and most of the other references including the 2006 Ranier PDF collection - incorrectly depict the D2 switch in the manifold pressure switch (most trans guys refer to this as the "pillow switch"). It is in fact a normally closed switch, which when D2 applies breaks the circuit grounding the D4 / D3 normally open switches. I got some white-out and fixed my printed copies so as not to chase ghosts should I get to looking at this one.
Got Rusty out of storage this morning and have the break-out cable and the newest TCM module in place. Starts and runs with no issues. That's as far as I got b/c I threw my back out pulling weeds this morning and after mowing my lawn that's about as far as I'm able to get.
Have a Hantek CC65 clamp-on current sensor on the way that should make visualizing solenoid currents much easier. Just need to find my BNC extension cable so I can feed it through the firewall along with some home-made test clip leads.
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Mooseman
Moderator
For manuals and schematics, have you tried this site?
Free Car Service Manuals from Operation CHARM — No strings attached!
Operation CHARM provides completely free repair/service/workshop manuals for over 50,000 models of cars and trucks manufactured 1982-2013. No sign-up or paywall.
charm.li
I haven't seen or heard of that, thanks! May come in handy some day.
Whatever the case, they all seem to basically be the same data packaged differently. I have to wonder how that information is licensed out, or if it's something freely available from the OEMs.
The first schematic I found on that site also incorrectly depicts the pillow switch, which I will add also has a normally closed switch for D3, according to this manual which apparently came directly from GM. (lower left corner, page 37)
Hydra-matic 4L60-E Tech Guide
You might want to add that to your manuals page as it seems slightly more comprehensive than the ATSG version.
Whatever the case, they all seem to basically be the same data packaged differently. I have to wonder how that information is licensed out, or if it's something freely available from the OEMs.
The first schematic I found on that site also incorrectly depicts the pillow switch, which I will add also has a normally closed switch for D3, according to this manual which apparently came directly from GM. (lower left corner, page 37)
Hydra-matic 4L60-E Tech Guide
You might want to add that to your manuals page as it seems slightly more comprehensive than the ATSG version.
Mooseman
Moderator
NP, happy to contribute.
Think my toolbox is finally equipped to tackle this problem.
Channel 1 is the switched IGN voltage that supplies power to the trans solenoids, and channel 2 is the 1-2 shift solenoid output. This was taken moments after starting the engine - the voltage jump at the beginning of the capture is the alternator starting to generate power. Interesting that the 1-2 shift solenoid is only energized after quite a bit of time has passed after key-on. I'll have to try quantifying that.
This isn't a lab grade DSO, but I wish I would have bought one of these years ago. There's no external trigger for the freeze / run function (that stops the sweep), but I'll get by with the big red button on the scope.
Think my toolbox is finally equipped to tackle this problem.
Channel 1 is the switched IGN voltage that supplies power to the trans solenoids, and channel 2 is the 1-2 shift solenoid output. This was taken moments after starting the engine - the voltage jump at the beginning of the capture is the alternator starting to generate power. Interesting that the 1-2 shift solenoid is only energized after quite a bit of time has passed after key-on. I'll have to try quantifying that.
This isn't a lab grade DSO, but I wish I would have bought one of these years ago. There's no external trigger for the freeze / run function (that stops the sweep), but I'll get by with the big red button on the scope.
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As I was hoping to at least be reporting I'm working through the process, it disappoints me to update that I'm nearly back to square one.
The breakout cable worked exactly as expected, and in combination with the DSO gave me the tools to capture some cool waveforms of startup and 1-2 shifts. But that's all it provided. Over the 350-odd miles I've driven with it in place, zero TCM issues were observed. Not even a hint of the PRNDL indicator moving unwarranted, doors unlocking, or the 1-2 shift solenoid losing power unexpectedly, causing the trans to go all but limp.
At this point it occurred to me that perhaps having the TCM branch of the harness out of place as it was moved some wires that were chafed to a favorable spot, or that the additional impedance of the wire and connectors of the breakout cable might be the key. So I removed the breakout cable and zip-tied the TCM to the battery tray so the harness was in roughly the same position so as to eliminate only the impedance variable.
Once again, several test drives proved uneventful. I found this to be a "good" sign, and pulled all the ECM / TCM connectors back out of the rat's nest and looked for signs of chafed wires near the red zip-tie that corresponds to the point a loom retainer clip holds the TCM branch down to the frame rail.
After going over every single wire between the TCM connector and the convergence with the ECM branches carefully with my lighted and articulated workbench magnifying glass and some mild contact cleaner on a paper towel (to clean the dirt off the wire jackets) I've come up with nothing. Absolutely nothing.
So I scoop my pride off the floor and decide to re-tape the harness and get it back in the split loom so I don't end up with something getting caught in a fan belt. Once all back to normal, for sh*ts and giggles I put the TCM back in its usual plastic carrier alongside the ECM and go for a short test drive from "cold" (current ambient temp is about 82F). Numerous incidents were observed (at least 6 in a 2 mile circuit of mixed 60mph highway and 25mph urban driving).
So for now, the "fix" to this problem seems to be zip-tying the TCM to the battery box. I'm beyond confounded.
The breakout cable worked exactly as expected, and in combination with the DSO gave me the tools to capture some cool waveforms of startup and 1-2 shifts. But that's all it provided. Over the 350-odd miles I've driven with it in place, zero TCM issues were observed. Not even a hint of the PRNDL indicator moving unwarranted, doors unlocking, or the 1-2 shift solenoid losing power unexpectedly, causing the trans to go all but limp.
At this point it occurred to me that perhaps having the TCM branch of the harness out of place as it was moved some wires that were chafed to a favorable spot, or that the additional impedance of the wire and connectors of the breakout cable might be the key. So I removed the breakout cable and zip-tied the TCM to the battery tray so the harness was in roughly the same position so as to eliminate only the impedance variable.
Once again, several test drives proved uneventful. I found this to be a "good" sign, and pulled all the ECM / TCM connectors back out of the rat's nest and looked for signs of chafed wires near the red zip-tie that corresponds to the point a loom retainer clip holds the TCM branch down to the frame rail.
After going over every single wire between the TCM connector and the convergence with the ECM branches carefully with my lighted and articulated workbench magnifying glass and some mild contact cleaner on a paper towel (to clean the dirt off the wire jackets) I've come up with nothing. Absolutely nothing.
So I scoop my pride off the floor and decide to re-tape the harness and get it back in the split loom so I don't end up with something getting caught in a fan belt. Once all back to normal, for sh*ts and giggles I put the TCM back in its usual plastic carrier alongside the ECM and go for a short test drive from "cold" (current ambient temp is about 82F). Numerous incidents were observed (at least 6 in a 2 mile circuit of mixed 60mph highway and 25mph urban driving).
So for now, the "fix" to this problem seems to be zip-tying the TCM to the battery box. I'm beyond confounded.
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I've been driving Rusty as I would any other auto-trans beater / commuter car over several days and for several hundred miles with the newest (i.e. new out of a sealed GM box) TCM module that seemed most susceptible to whatever problem has been plaguing the vehicle, only relocated from it's original plastic holder next to the ECM / radiator, to being zip-tied to the battery box.
It pains me to state this, but I'm starting to believe the problem is / was triggered by the location of the TCM. Considering I spent at least 8-10 hours "fiddling" with every wire going to the TCM to no avail after re-locating, I feel like I've covered all the faulty wiring scenarios. The only change that seems to bring definite results has been the relocation of the TCM closer to the battery tray.
As much as I'm reluctant to declare this the solution, after sleeping on it I realized that aside from the ECM, the electro-viscous fan clutch is the only other source of EMI in the vicinity of the TCM. It's control signal is also PWM controlled based on engine coolant temperature (as well as A/C pressures and trans fluid temps).
I'll report back if things change, but I'm feeling like this is a solution, albeit one I would not accept under normal circumstances.
I'll post back every few months, or if the problem recurs. But for now I'm planning on fixing all the other issues except disabling AFM (mainly a leaky rear air spring and rust-dissolved upper trailing arm mounts) and driving it 1700 miles to and from our favorite vacation spot this coming August.
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Mooseman
Moderator
Usually when the EV fan fails, it kills the throttle system and puts it in reduced power mode. However, this is on the 4.2. Haven't heard of the 5.3 being affected the same way.
I have never heard of of a PCM or TCM being affected by EMI.
Have you tried using some contact cleaner on the TCM pins and in the connector? Another possibility is a wire that's broken internally but losing contact intermittently and moving the TCM puts the wire loom in a position to keep that wire in contact.
I have never heard of of a PCM or TCM being affected by EMI.
Have you tried using some contact cleaner on the TCM pins and in the connector? Another possibility is a wire that's broken internally but losing contact intermittently and moving the TCM puts the wire loom in a position to keep that wire in contact.
Perhaps true, but the 5.3 with the E38/T42 combination was only in production in limited numbers from late 2005 to the platform's unfortunate demise.
I'm far more confounded than you could know. Yet I've thus far found no other logical explanation.
I absolutely tried contact cleaner on just about everything. I even used it to clean the vehicle harnesses' wire jackets while I was inspecting them for fraying / discoloration / etc.
Not to mention I've added a complete sub-harness between a brand-new TCM and the existing vehicle harness, complete with two used male and female ends, both of which were seriously "cobbled together". If anything this would ADD resistance / problems. But despite my best efforts no amount of manipulation of wires (even down to the 1/2" closest to the connector pins) could reproduce the problem with the sub-harness in place / TCM relocated.
Trust me, having run into that type of problem at least twice in the past several years, that is exactly what my focus was set to finding when I started into this. As such I went over every "suspect" bit of wire (discolored jacket, etc.) looking for the tell-tale feel of a jacketed wire with an internal break. I've been there and done that, and I wish it was that simple.
Edit: The scientist in me expects, and somewhat hopes to be proven wrong. I'm simply posting my current observations.
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Mooseman
Moderator
Maybe time to wrap it with a tin foil hat 
. You could try unplugging the fan and see if it resolves it. As long as it's not too hot out and not run the A/C, you should be fine and keep an eye on the temps. You will get a code for the fan.
I would have lost it too by now.
. You could try unplugging the fan and see if it resolves it. As long as it's not too hot out and not run the A/C, you should be fine and keep an eye on the temps. You will get a code for the fan.I would have lost it too by now.
Maybe time to wrap it with a tin foil hat
Right?
Ironic that you'd mention that. Though I only drove it a few hundred miles before getting the A/C working, this problem did not surface until after that. As I mentioned (possibly in the other thread) I've noticed the issue apparently coinciding with the A/C compressor clutch engaging or disengaging but not in a repeatable manner. But I've also had it happen with the climate control turned off completely.
It's due for an oil change so I might test with the fan clutch disconnected just for the hell of it.
Well I'm not at all surprised to report that disconnecting the fan clutch accomplished nothing except that I discovered someone had poorly cobbled a repair of the wiring right at the connector, likely the result of a water pump bearing failure. Whatever mental midget did this didn't feel the ground wire needed to be fixed, so the bare parts of it had frayed and broken, though not completely.
Anyway... before the post-oil change test drive, while I was clearing the fan speed sensor code I noticed an odd noise like the compressor clutch was cycling though the climate control was off. I get out and put my eyes and ears to work, and find the sound appears to be coming from the transmission. Lo and behold as I shift into neutral I witness the PRNDL indicator doing it's usual dance. So this seems to indicate it happens when in park also. (TCM was in it's intended location)
Basic reasoning would suggest that if the only thing I touched pertaining to the wiring harness was moving the TCM and it's branch a few inches higher and towards the driver side, wiggling said harness in it's new location should reproduce the problem. But it doesn't.
I've yet to work up the courage to try doing the same with the TCM loose but near it's intended location, because meeting flesh with the un-shrouded part of the spinning fan isn't all that appealing.
Edit: just for clarity, I have used a coat hanger to manipulate the TCM harness while in it's intended location to no result.
For now I'm going to drive with the knowledge that two zip-ties are just a band-aid. But the band-aid makes the boo-boo fixed, at least until it isn't. I wish I understood why, but as long as the problem appears "patched" I'm not going to let it further accelerate my achromotrichia.
Anyway... before the post-oil change test drive, while I was clearing the fan speed sensor code I noticed an odd noise like the compressor clutch was cycling though the climate control was off. I get out and put my eyes and ears to work, and find the sound appears to be coming from the transmission. Lo and behold as I shift into neutral I witness the PRNDL indicator doing it's usual dance. So this seems to indicate it happens when in park also. (TCM was in it's intended location)
Basic reasoning would suggest that if the only thing I touched pertaining to the wiring harness was moving the TCM and it's branch a few inches higher and towards the driver side, wiggling said harness in it's new location should reproduce the problem. But it doesn't.
I've yet to work up the courage to try doing the same with the TCM loose but near it's intended location, because meeting flesh with the un-shrouded part of the spinning fan isn't all that appealing.
Edit: just for clarity, I have used a coat hanger to manipulate the TCM harness while in it's intended location to no result.
For now I'm going to drive with the knowledge that two zip-ties are just a band-aid. But the band-aid makes the boo-boo fixed, at least until it isn't. I wish I understood why, but as long as the problem appears "patched" I'm not going to let it further accelerate my achromotrichia.
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Just updating that after ~450 miles of mixed driving (mostly interstate) zero issues have been observed. It rolled over 200k miles on Sunday and touching wood, only one lifter is ticking very mildly at idle (quiets down above 800 rpm). July heat arrived two weeks early so I've been exercising the A/C extensively.
Working on replacing the air springs this afternoon. It's gonna be a 2 or 3 shirt job.
Edit: Just noticed the thread has been marked "solved", which may be premature. No need to change that, I'll come back in a year if not sooner.
Air springs are swapped for Arnott 2nd design. I was shocked to find the passenger side was still the GM original with permanently crimped air line, at 18 years and 200,007 miles! Everything's working great, but I'm worried some day I may find the compressor motor shell laying in my driveway in the form of a pile of rust "crumbles".
Working on replacing the air springs this afternoon. It's gonna be a 2 or 3 shirt job.
Edit: Just noticed the thread has been marked "solved", which may be premature. No need to change that, I'll come back in a year if not sooner.
Air springs are swapped for Arnott 2nd design. I was shocked to find the passenger side was still the GM original with permanently crimped air line, at 18 years and 200,007 miles! Everything's working great, but I'm worried some day I may find the compressor motor shell laying in my driveway in the form of a pile of rust "crumbles".
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Just dropping in with another update. Replaced the rear upper trailing arm mounts a few weeks prior and couldn't be happier with the outcome.
After that project we drove the Envoy ~1750 miles round-trip on vacation last week and zero issues save for one of the original front wheel bearings giving up the ghost. It was making a whirring sound when we left that I suspected was either a problem with the power steering pump or the transmission pump. Only after the initial ~500 miles getting to Mississippi did it become pronounced enough I could tell it was a wheel bearing. S/He got us home unscathed and a new pair of Timken wheel hubs / bearings were waiting for me when I backed into the garage. Installed them this afternoon and found both sides appeared to be the original factory parts from 2006.
Now I just need to find a replacement for the air ride compressor and I should be set for a good while!
Seriously happy to find the 5.3 v8 used essentially the same amount of fuel as the 6-cylinder Trailblazer has in the past for the same vacation trip. The Envoy was far more fun to drive with it's 3.73 gearing and fatter torque curve. There were stretches where the cruise control was engaged for more than 2 hours without so much as the torque converter unlocking. I feel like I've won the rusty used vehicle lottery with this one!
It's been run about 4k miles since I relocated the TCM, and have had zero issues. As this problem is / was temperature dependent I won't declare it "solved" until it makes it through another winter and spring, but so far, so good! I just wish I knew why moving the module made a difference when nothing else did. I left no stone un-turned when looking over the wiring between the TCM and the main harness.
After that project we drove the Envoy ~1750 miles round-trip on vacation last week and zero issues save for one of the original front wheel bearings giving up the ghost. It was making a whirring sound when we left that I suspected was either a problem with the power steering pump or the transmission pump. Only after the initial ~500 miles getting to Mississippi did it become pronounced enough I could tell it was a wheel bearing. S/He got us home unscathed and a new pair of Timken wheel hubs / bearings were waiting for me when I backed into the garage. Installed them this afternoon and found both sides appeared to be the original factory parts from 2006.
Now I just need to find a replacement for the air ride compressor and I should be set for a good while!
Seriously happy to find the 5.3 v8 used essentially the same amount of fuel as the 6-cylinder Trailblazer has in the past for the same vacation trip. The Envoy was far more fun to drive with it's 3.73 gearing and fatter torque curve. There were stretches where the cruise control was engaged for more than 2 hours without so much as the torque converter unlocking. I feel like I've won the rusty used vehicle lottery with this one!
It's been run about 4k miles since I relocated the TCM, and have had zero issues. As this problem is / was temperature dependent I won't declare it "solved" until it makes it through another winter and spring, but so far, so good! I just wish I knew why moving the module made a difference when nothing else did. I left no stone un-turned when looking over the wiring between the TCM and the main harness.
Mooseman
Moderator
For the rear bag system, I suggest just replacing them with regular springs. Today it's the compre$$or, tomorrow will be the bag$ themselves. It's an expensive system to repair, springs are cheap.
Bags were replaced earlier this year due to one leaking. The driver side had been replaced previously but the passenger side was the OE part.
Had I looked more closely at the compressor before buying the bags I might have thought differently. The shell of the motor is in rough shape (rust).
Had I looked more closely at the compressor before buying the bags I might have thought differently. The shell of the motor is in rough shape (rust).
Not that old... I'll let you know. Mods prematurely marked the thread "solved". Now that the ambient temps are dipping into the 50s for lows, I'm noticing the problem resurface. Thankfully I have all the tools at hand to troubleshoot.
Edit: Are you experiencing the problem yourself?
Edit: Are you experiencing the problem yourself?
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Mooseman
Moderator
It is unsolved.Changed the oil and rotated tires today. While I had the front on jackstands I debated looking again underneath for potential loose grounds. Then I decided to say f-it, run a couple errands and then go wash the bug juice off the windshield after the Florida trip. It's a gorgeous day - the overnight low was 53F and even now at 1 PM it's only 75F. Hasn't been this cool since... a few weeks before I relocated the TCM module and it seemed to remedy the issue.
On the 2 mile drive to pay my municipal utilities it clicked the locks a bunch and finally set a P0601-00 (TCM rom memory error) and the TCM went into limp mode. Knowing that the only thing that's changed is the weather, the notion that there's a temperature component seems now to be solidly confirmed. I haven't noted a single hiccup all summer since relocating the TCM.
Then I re-read this thread numerous times and recapped everything I've done / witnessed.
I think my next course of action is to try to find a TCM connector branch from a salvage yard. My guess is that there's a female terminal in the connector that's not quite producing enough tension on the pin coming out of the TCM. But just in case I'm going to try and find one intact so I can cob the entire ECM + TCM branches (four total) so I can splice back far enough to fix some of the stupid wire routing I noticed when I stripped the entire engine harness bare back in April. My thinking is the more wire I replace, the better my chances are.
I just hope I can find a donor vehicle that isn't in the salvage yard for the same reason I'm working so hard to keep mine out of one. Wish me luck?
On the 2 mile drive to pay my municipal utilities it clicked the locks a bunch and finally set a P0601-00 (TCM rom memory error) and the TCM went into limp mode. Knowing that the only thing that's changed is the weather, the notion that there's a temperature component seems now to be solidly confirmed. I haven't noted a single hiccup all summer since relocating the TCM.
Then I re-read this thread numerous times and recapped everything I've done / witnessed.
I think my next course of action is to try to find a TCM connector branch from a salvage yard. My guess is that there's a female terminal in the connector that's not quite producing enough tension on the pin coming out of the TCM. But just in case I'm going to try and find one intact so I can cob the entire ECM + TCM branches (four total) so I can splice back far enough to fix some of the stupid wire routing I noticed when I stripped the entire engine harness bare back in April. My thinking is the more wire I replace, the better my chances are.
I just hope I can find a donor vehicle that isn't in the salvage yard for the same reason I'm working so hard to keep mine out of one. Wish me luck?
Mooseman
Moderator
An internal error, PCM or TCM, is pretty certain that the module is faulty. Without going through the thread, did you try replacing the TCM? It has to be from a same type and year truck.
As I genuinely appreciate your input, I would encourage you to carefully re-read this thread from beginning to now. Yes, I've replaced the TCM. Multiple times. They're not killing themselves of their own volition, and the ROM errors are happening because the module's power supply is getting slammed with something during the only time the flash (ROM memory) is tested, during power-on / wake-up.
Mooseman
Moderator
OK, maybe a wiring short is sending 12V into a 5V reference line and frying things? You've even said yourself moving the harness seems to make it better. Just throwing things out there and seeing if something sticks. Maybe something in the tranny harness?
I think we're just as exasperated as you are.
I think we're just as exasperated as you are.
wrap a ice pack (insulated) around the TCM. Based on your premise, the system should go wacko regardless of where the tcm is located.
budwich I didn't see your suggestion when posted several weeks ago, sorry. I wasn't implying that the T42 module temperature is directly connected to the problem. That doesn't appear to be the case or I would have had all sort of difficulties with it last winter during cold starts. What happens is once at operating temperature, when the vehicle sits and cools down for several hours, the problem becomes more reproducible. It seems ambient temps make this phenomenon even more apparent.
Yesterday I set out to try and reproduce the problem, as I've been noticing two or three singular PRNDL indicator events just about every day for the last few weeks, usually when leaving work to get lunch (and the vehicle having sat and cooled off for 2-3 hours).
I removed the plastic cover from the back of the connector, removed the zip-tie securing the bundle to the connector base, and peeled back the split loom about 1/2 the distance to the point it converges with the ECM branches. Then drive a short loop around town, and stop at my classmate's house while he's unloading his mower (Russ is pro mechanic, but these are the type of problems he runs from screaming "not me!"). Talk to him for 10 minutes or so and then head five or six blocks towards the convenience store. One PRNDL event happened about three blocks away. Then two more after leaving the convenience store. Thinking I'm not at the right ambient temperature to witness the problem acutely, I park it in the garage and sit things out for a couple hours. Later on I make another trip to the same c-store. As I'm pulling in the lot over the uneven concrete around the fuel tank bulkheads the check engine light illuminates and it becomes apparent it's in limp mode again. If memory serves this is the same spot where I got into limp mode three weeks ago. So chassis flex also seems to be a component.
Since I had plans afterward I wasn't able to do any immediate prodding, but did notice that I could no longer clear the P0604 DTC. Further attempts this morning confirm, I've KILLED another T42. That makes two, I'm down to using my only spare.
I'd like to think it's something as simple as a loose ground, but I've added a supplemental ground between the battery ground strap on the fender and the T42 case earlier this year and it made no difference. The G108 eyelet and bolt are rock solid, as is the main battery ground and no symptoms are noticed when I manipulate either wire. Furthermore, the E38 (engine control module) is also grounded through this same G108 circuit, and I've never experienced any random engine performance issues / DTCs.
I've also split both front and rear fuseblocks and checked for cracked / intermittent shunts. The ones that are internal to the "sandwich" that supply power to TCM pin 31 or 32 I jumpered around with a fuse tap to B+.
My only other thought is perhaps theres a problem with the ISS internal to the transmission. It appears to be a powered hall sensor (three wires). I've replaced the internal harness up to the ISS connector, but as this piece lives inside the pump, it's not something I can easily get to. My thought was to try disconnecting both pins and see whether this also puts the TCM in limp mode. Unfortunately the pins for these connectors can't be removed without cutting the wire. I'm keeping this one in the back of my mind, because if the wiring is somehow exposed internally such that clutch material can build up between bare terminals, that could be a possible cause of intermittent shorting. The suck here is if I pull the tranny out to look at that it's going to get a $1500+ rebuild with a hardened sunshell and z-pack 3rd clutches, etc.
As I'm completely out of easily workable ideas on this, I think I'm goign back to the idea of replacing the entire TCM branch. With the exception of the ground, all the other wires terminated in this connector are very supple 22 or 24 gauge stranded wire. It's entirely possible one or more are partially fused or frayed internally and it would be next to impossible to discern this visually. As mentioned previously I've gone over the powertrain harness from the rear O2 sensors all the way to the fuseblock and ECM / TCM branch and found nothing blatantly obvious.
I've rarely thrown in the towel on a decent used vehicle, but I've reached the point where it would be easier to do that here. I just really, really like this one. Also, I'm well beyond the reasonable threshold of the "sunk cost fallacy".
Yesterday I set out to try and reproduce the problem, as I've been noticing two or three singular PRNDL indicator events just about every day for the last few weeks, usually when leaving work to get lunch (and the vehicle having sat and cooled off for 2-3 hours).
I removed the plastic cover from the back of the connector, removed the zip-tie securing the bundle to the connector base, and peeled back the split loom about 1/2 the distance to the point it converges with the ECM branches. Then drive a short loop around town, and stop at my classmate's house while he's unloading his mower (Russ is pro mechanic, but these are the type of problems he runs from screaming "not me!"). Talk to him for 10 minutes or so and then head five or six blocks towards the convenience store. One PRNDL event happened about three blocks away. Then two more after leaving the convenience store. Thinking I'm not at the right ambient temperature to witness the problem acutely, I park it in the garage and sit things out for a couple hours. Later on I make another trip to the same c-store. As I'm pulling in the lot over the uneven concrete around the fuel tank bulkheads the check engine light illuminates and it becomes apparent it's in limp mode again. If memory serves this is the same spot where I got into limp mode three weeks ago. So chassis flex also seems to be a component.
Since I had plans afterward I wasn't able to do any immediate prodding, but did notice that I could no longer clear the P0604 DTC. Further attempts this morning confirm, I've KILLED another T42. That makes two, I'm down to using my only spare.
I'd like to think it's something as simple as a loose ground, but I've added a supplemental ground between the battery ground strap on the fender and the T42 case earlier this year and it made no difference. The G108 eyelet and bolt are rock solid, as is the main battery ground and no symptoms are noticed when I manipulate either wire. Furthermore, the E38 (engine control module) is also grounded through this same G108 circuit, and I've never experienced any random engine performance issues / DTCs.
I've also split both front and rear fuseblocks and checked for cracked / intermittent shunts. The ones that are internal to the "sandwich" that supply power to TCM pin 31 or 32 I jumpered around with a fuse tap to B+.
My only other thought is perhaps theres a problem with the ISS internal to the transmission. It appears to be a powered hall sensor (three wires). I've replaced the internal harness up to the ISS connector, but as this piece lives inside the pump, it's not something I can easily get to. My thought was to try disconnecting both pins and see whether this also puts the TCM in limp mode. Unfortunately the pins for these connectors can't be removed without cutting the wire. I'm keeping this one in the back of my mind, because if the wiring is somehow exposed internally such that clutch material can build up between bare terminals, that could be a possible cause of intermittent shorting. The suck here is if I pull the tranny out to look at that it's going to get a $1500+ rebuild with a hardened sunshell and z-pack 3rd clutches, etc.
As I'm completely out of easily workable ideas on this, I think I'm goign back to the idea of replacing the entire TCM branch. With the exception of the ground, all the other wires terminated in this connector are very supple 22 or 24 gauge stranded wire. It's entirely possible one or more are partially fused or frayed internally and it would be next to impossible to discern this visually. As mentioned previously I've gone over the powertrain harness from the rear O2 sensors all the way to the fuseblock and ECM / TCM branch and found nothing blatantly obvious.
I've rarely thrown in the towel on a decent used vehicle, but I've reached the point where it would be easier to do that here. I just really, really like this one. Also, I'm well beyond the reasonable threshold of the "sunk cost fallacy".
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