Speed sensor problem, the saga continues...

jmonica

Original poster
Member
Apr 2, 2013
384
Hamburg, NJ
Hi, After getting the transmission and everything put in and back together, I now have a P0502, no speedo and upshifting happens but very late and well it's just not right. I have an awful feeling I may have damaged one of the wires and in a place that's not easily accessible. I accidentally pulled on one of them. I repaired it, (soldered and heat shrink), but I'm really afraid I might have pulled on it so that it broke way up further in the harness as well in which case, I am screwed I think.
My other problem is that I think I ran the wires to the transfer case wrong. There was one wire that was clamped to the bracket that holds the exhaust in place. But the way I have them run now, on top of the TC, there's no wire that would possibly reach that clamp on the exhaust bracket so I don't know what I did wrong. I'm just disgusted with myself at this point. I can't get a single person to come and lend me a hand. I'm running out of steam on this project to be honest. It was supposed to be a trans swap and turned into a trans rebuild (did it myself), power steering pump replacement, PS cooler, radiator, wheel speed sensor, ball joints, brake job, rust removal project along the way. Plus it's cold as heck lately and it makes working on it with no heater in the garage a pain when it's 15 degrees out.
Sorry for the rant.

So I guess my first question is, does anyone happen to know if the 3 speed sensors on the transfer case all share the same part number?

Thanks in advance.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
I've seen this on a full size, the front and rear speed sensor connectors are the same and were swapped. Swapping them around should fix it (if it's the same as full size)
 
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jmonica

Original poster
Member
Apr 2, 2013
384
Hamburg, NJ
I've seen this on a full size, the front and rear speed sensor connectors are the same and were swapped. Swapping them around should fix it (if it's the same as full size)
Ohh really? Thank You. I can't wait to get out there and try it. If this fixes the problem, man You are a lifesaver and I will give you my sister. I will report back the results. Thanks so much man!
BTW.. I can confirm that the connectors are the same and appeared to be interchangeable if i remember correctly. Thank You again Mooseman!
 
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Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
I will give you my sister.

I don't think Mrs. Moose would appreciate that however I do like a nice whisky :biggrin:

Do report back if that fixes it.
 
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TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,047
Brighton, CO
...and I will give you my sister. I will report back the results.

Reporting back the results of giving your sister to Moose... This should be interesting!

I don't think Mrs. Moose would appreciate that however I do like a nice whisky :biggrin:

Do report back if that fixes it.

Whiskey?! Wheres the fun in that.. I could always use a house servant, or something!
 

jmonica

Original poster
Member
Apr 2, 2013
384
Hamburg, NJ
I still haven’t been able to get out to the garage and try this but I’m hopeful Thursday is the day. I’m sick as a dog this past two days. Will for sure report back.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
C'mon, it's Christmas. What else have you got to do today? :biggrin:
 

jmonica

Original poster
Member
Apr 2, 2013
384
Hamburg, NJ
I hear ya man. I’m acting like a wimp. I’mg fever is still up over 100 but I feel a little better. By tomorrow night im gonna get rid of the p0502 and P0443 and start cleaning and cleaning. Putting in new carpets to start. Will post pics. Hope you’re having a great holiday and drive safe!
 
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jmonica

Original poster
Member
Apr 2, 2013
384
Hamburg, NJ
I've been online for hours trying to find out how I can figure out where the VSS wire goes from the transfer case. I have a P0502 code. I was hoping I just had some wires connected wrong as Mooseman suggested I might. In fact he was right (as usual), I did have the main VSS connector switched with the Rear Speed sensor. Excited thinking my worries were over, sadly for me, it didn't fix the problem,. Code came right back, and no speedo, and late up-shift into 2nd. I also replaced all 3 speed sensor on the transfer case with no change.
My next mission is to trace the wire to see if it's broken between the TC and where it ends up. Th problem is i cannot figure out (on paper) where it goes? I have like 7 wiring diagrams, none of which tell me what I need to know. Short of separating every piece of plastic insulation and tracing the wire along its path, I was hoping to be able to do some continuity testing to track it down.

One of the diagrams says,
"4.2L: The PCM is attached to the driver side of the engine. VSS is in pin 21.
Speed Sense dk. green/white cluster or PCM/ECM,
blue plug
"

So should I be able to check for continuity between the VS Sensor connector and in 21 of the blue PCM section? Does "Speed Sense" even indicate the VSS? Is it that easy? I doubt it. I can confirm that one of the wires from the connector is Green. The other one is Purple. My small brain is fried man. Can anyone provide any tips or help? Please? Thanks in advance! Jim

I'm also getting a code P0443 ( ECR Purge Valve) and C0455 (chronic Service Stabilitrac been there for many years and 2 new SWPS's. I don't think they are related but what do I know?
 

Mounce

Member
Mar 29, 2014
13,667
Tuscaloosa, AL
From what I can gather from two seperate resources...

Front sensor wire color is yellow and purple.
Rear senor is light-blue and dark-green.

Both resources show that both sensors feed into the TCCM through the Grey connector, however the pcm also shows a VSS input but I think that's for 2wd models. Only thing I see coming from the TCCM that would seem to connect it to the pcm is one class 2 data bus wire, which in turn would put it on the same channel as the cluster, etc. Every other pin on the TCCM is disconnect control, encoder controls/feedback, and 4wd selector position and light outputs plus some power, grounds, and references.

Done some more digging and confirmed that the pcm vss inputs I see are from a sensor on the trans, not transfer case.

One last thing. When these wires leave the transfer case they go through c101 which is the big connector by the front fuse block before they get to the TCCM.
 
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TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,047
Brighton, CO
Do you know that the output from the transmission is working? The gear/tone ring could be faulty, or out of range. Just a thought.
 
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Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Posts moved to your existing thread.

Since you did a tranny swap, I would concentrate on that end of the wiring. Did you inspect the pins in the sensor? Check the wires at the connector and of course, trace the wires for continuity. It could also be possible that the sensor itself is no bueno. If the two sensors are the same, maybe try swapping them around. Ensure you have the correct colour wired connectors to the right sensors according to what @Mounce said.
 
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jmonica

Original poster
Member
Apr 2, 2013
384
Hamburg, NJ
From what I can gather from two seperate resources...

Front sensor wire color is yellow and purple.
Rear senor is light-blue and dark-green.

Both resources show that both sensors feed into the TCCM through the Grey connector, however the pcm also shows a VSS input but I think that's for 2wd models. Only thing I see coming from the TCCM that would seem to connect it to the pcm is one class 2 data bus wire, which in turn would put it on the same channel as the cluster, etc. Every other pin on the TCCM is disconnect control, encoder controls/feedback, and 4wd selector position and light outputs plus some power, grounds, and references.

Done some more digging and confirmed that the pcm vss inputs I see are from a sensor on the trans, not transfer case.

One last thing. When these wires leave the transfer case they go through c101 which is the big connector by the front fuse block before they get to the TCCM.
Thanks for taking the time to reply. The 4wd models have three speed sensors on the Transfer case. A Front, a rear and the main VSS (two wires are green/blk and Purple. The main VSS is on the tail housing of the TC. Everything that I have read indicates that's probably the culprit so i am going to try to trace that wire and see what happens. If I can find a break in continuity, I will run a new wire, bypassing the break and see if that fixes the problem. I will report back and let everyone know what I discover. Thank You again and happy new year!
 

jmonica

Original poster
Member
Apr 2, 2013
384
Hamburg, NJ
Posts moved to your existing thread.

Since you did a tranny swap, I would concentrate on that end of the wiring. Did you inspect the pins in the sensor? Check the wires at the connector and of course, trace the wires for continuity. It could also be possible that the sensor itself is no bueno. If the two sensors are the same, maybe try swapping them around. Ensure you have the correct colour wired connectors to the right sensors according to what @Mounce said.

Thanks Mooseman. I replaced all three of the TC Speed sensors. I checked the old ones for resistance after swapping them, just for fun and they all appeared to be within range.

I have checked the connector(s) fairly closely but will give that another go tonight.

I agree that common sense says that the problem was brought on by the trans swap so its got to be related. Unless I am just REALLY unlucky.

I didn't think it would be that hard to figure out where that wire goes after it leaves the TC but it proved difficult on paper at least. The answer to that simple question would tell me everything that I need to fix it. I'll just have to figure it out on my own I think. I am hoping it goes directly to the PCM.

That's what I spent hours trying to figure out last night and it seems like nobody knows the answer. The diagrams seem to conflict. I am not confident that it goes to the TCCM from the sensor as some have suggested. ( I won't elaborate and bore you why I think that).

I had mentioned earlier that I accidentally pulled on one of the wires and broke it during the swap. Then I repaired it. I'd be stunned if it turned out my repair was faulty. I did it right with a Lineman's splice of the wires, soldered it, heat shrunk it, then put new plastic sleeving on it. I am fairly confident there's another break some place further up the harness because of it.

So some advice please? Does this sound like a logical plan to you???
1. Check the PCM for the wires on pins 20 and 21. If they are the same color, and match my diagram, they "should" be the correct ones?
2. Check for cont. between the PCM wires and and the sensor connector.
3. If no cont, I will temporarily bypass the wire with a long jumper wire from sensor to PCM to test vehicle. If it fixes it, then I will start tracking down the location of the wire break and fix it correctly.

OR

4. If yes I have cont between the sensor connector and the PCM, then I will start investigating other possibilities. Maybe even a bad PCM or at least dirty and corroded?

The car sat for 16 months only being started a few times and everything on it took a beating from corrosion and rusting etc.

Thanks again!
 

jmonica

Original poster
Member
Apr 2, 2013
384
Hamburg, NJ
Do you know that the output from the transmission is working? The gear/tone ring could be faulty, or out of range. Just a thought.
Hi Thanks for the reply. I don't know to be honest. On the 4WD model the transfer case VSS is responsible for reporting back the speedo and operating the speedo etc... I think that only the 2WD model uses a speed sensor located on the transmission. Is that what you are referring to when you say Gear/Tone ring? For the Transfer Case sensor, I was under the impression that they pick up their reading magnetically from the out spline itself? At least that's how I have it pictured in my head. I could be completely wrong as I frequently am. Thank You again for replying!
 

TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,047
Brighton, CO
The magnet you are talking about is part of the tone ring. If it is gummed up, with sludge, grease, or magnet fragments, it will give a false reading.

Happens quite frequently with ABS sensors
 
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Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Looked up some schematics and found that the VSS is located at the rear of the TC and has LT GRN/BLK and PPL/WHT wires. They go to the PCM on connector C3 on pins 44 and 45 same colours respectively. Found this in the schematics for the Cruise Control and confirmed on the main PCM schematics.

A quick test would be to test the resistance at pins 44 and 45 to see if it matches the sensor's (or close to it). If you want, you can do it the normal way to be sure.

If that checks out, I would suspect the tone ring in the TC tail shaft, as @TollKeeper indicated. You can try swapping the connectors front and rear and put it in 4HI (you will get crow hop in turns). That will make the front shaft spin while driving and should give a speed reading.
 
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Mounce

Member
Mar 29, 2014
13,667
Tuscaloosa, AL
There's a reluctance wheel on one of the components inside at each sensor location just like for the crank sensor. The steel teeth on these wheels passing the sensors creates AC voltage in the sensors which is the signal that the computers read.

So, this all started after a trans swap? Or transfer case swap? One of the techs at another location in the company I work for put a reman transfer case in a jeep or something and ran into these same issues, the remanufacturer left out the reluctor wheel and caused the same path of diagnostics. Not saying that is your issue as well but if you put a new transfer case in I'd be inclined to peek into the sensor holes and see if the wheel exists.
 
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TJBaker57

Member
Aug 16, 2015
2,897
Colorado
I think you said you replaced some of the sensor wiring??

There was a bulletin addressing a condition where some vss wiring needs repair/replacement. Of particular interest is the details of the twisted pair.

Seems unlikely the twist or lack thereof in your replaced section of wiring would be enough to cause your issue but it couldn't hurt to adhere to the stated specification of 9 twists per foot.

 

jmonica

Original poster
Member
Apr 2, 2013
384
Hamburg, NJ
I think you said you replaced some of the sensor wiring??

There was a bulletin addressing a condition where some vss wiring needs repair/replacement. Of particular interest is the details of the twisted pair.

Seems unlikely the twist or lack thereof in your replaced section of wiring would be enough to cause your issue but it couldn't hurt to adhere to the stated specification of 9 twists per foot.


Thank You. I did see and read that bulletin. The reason I don't think that it is that the wire where it broke didn't look any different than any other normal, wiring. I do understand the reason for twisted pair wire from my knowledge of networking. I am going to do the testing you recommended above first and go from there. Just got to wait until my Son hits the sack first and he just commented about "having" to stray up until midnight to watch the ball drop. Yawn...Thank You again!
 

jmonica

Original poster
Member
Apr 2, 2013
384
Hamburg, NJ
The magnet you are talking about is part of the tone ring. If it is gummed up, with sludge, grease, or magnet fragments, it will give a false reading.

Happens quite frequently with ABS sensors
Ahh Thank You. This was a trans swap. Using a rebuilt transmission and my existing transfer case which was working prior to the trans failure. Now that you've pointed me in the right direction, I have something to go on and will start doing some more research. Thank You TollKeeper!
 

jmonica

Original poster
Member
Apr 2, 2013
384
Hamburg, NJ
Looked up some schematics and found that the VSS is located at the rear of the TC and has LT GRN/BLK and PPL/WHT wires. They go to the PCM on connector C3 on pins 44 and 45 same colours respectively. Found this in the schematics for the Cruise Control and confirmed on the main PCM schematics.

A quick test would be to test the resistance at pins 44 and 45 to see if it matches the sensor's (or close to it). If you want, you can do it the normal way to be sure.

If that checks out, I would suspect the tone ring in the TC tail shaft, as @TollKeeper indicated. You can try swapping the connectors front and rear and put it in 4HI (you will get crow hop in turns). That will make the front shaft spin while driving and should give a speed reading.
AWESOME, Thank You! This is going to help me diagnose the problem so much easier I will report back when it done Once again, you have proved yourself to be a prince amongst men! Thank You and if you go out for New Years tonight, be safe man! Happy New Year!!!
 

budwich

Member
Jun 16, 2013
2,027
kanata
It might be useful to just do some simple resistance checks. You have three sensor (as posted). Do some resistance metering on each sensor at the plug(s). First toward the sensor and then towards the "far end" and compare the results (of course, you do this with the plug disconnected and unpowered). It may not show much but on the other hand may readily point in a direction for next steps.
 

jmonica

Original poster
Member
Apr 2, 2013
384
Hamburg, NJ
It might be useful to just do some simple resistance checks. You have three sensor (as posted). Do some resistance metering on each sensor at the plug(s). First toward the sensor and then towards the "far end" and compare the results (of course, you do this with the plug disconnected and unpowered). It may not show much but on the other hand may readily point in a direction for next steps.
Yes Thank You. What you described is exactly my intention.
I replaced all 3 speed sensors with new ones. For the heck of it I tested all three of the sensors I pulled out and they are all exactly within spec, so now that Mooseman was kind enough to provide me with the worining info i needed, my place is to also do a continuity check from the sensor connection to the end point which is the pcmcia, then just start working backwards down the wire until I get a connection or continuity to pinpoint the break in the wire. Assuming of course the initial test indicates an open circuit between the two end points. Thanks again!
 

jmonica

Original poster
Member
Apr 2, 2013
384
Hamburg, NJ
Looked up some schematics and found that the VSS is located at the rear of the TC and has LT GRN/BLK and PPL/WHT wires. They go to the PCM on connector C3 on pins 44 and 45 same colours respectively. Found this in the schematics for the Cruise Control and confirmed on the main PCM schematics.

A quick test would be to test the resistance at pins 44 and 45 to see if it matches the sensor's (or close to it). If you want, you can do it the normal way to be sure.

If that checks out, I would suspect the tone ring in the TC tail shaft, as @TollKeeper indicated. You can try swapping the connectors front and rear and put it in 4HI (you will get crow hop in turns). That will make the front shaft spin while driving and should give a speed reading.
Hi Moose. Just wanted to let you know that I pried my wallet open and signed up for an online service that provides factory manuals, diagrams etc for my envoy. When you said you had spent time digging around for that wire location for me. I thought, I shouldn't be wasting your time with stuff like that. I don't know how good the service is, but can say it conformed exactly what you said in terms of pin outs etc... so I trust it. It was only $20 for the year so I'll just spend my boring summer days at work printing every single thing available. Anyway just wanted to sat that if you or anyone needs info on anything, I'm happy to look it up or send PDF's of anything they have, so don't hesitate to ask.
The website is alldatadiy.com so far so good. Thanks
 
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budwich

Member
Jun 16, 2013
2,027
kanata
Yes Thank You. What you described is exactly my intention.
I replaced all 3 speed sensors with new ones. For the heck of it I tested all three of the sensors I pulled out and they are all exactly within spec, so now that Mooseman was kind enough to provide me with the worining info i needed, my place is to also do a continuity check from the sensor connection to the end point which is the pcmcia, then just start working backwards down the wire until I get a connection or continuity to pinpoint the break in the wire. Assuming of course the initial test indicates an open circuit between the two end points. Thanks again!
I don't think you understand... you don't have to do anything at the pcm. Just do the same resistance measurement on the same "pin pairs" going towards the pcm... don't disconnect at the pcm. The results may tell you that you have broken wires or not... but you can go from there.
 
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jmonica

Original poster
Member
Apr 2, 2013
384
Hamburg, NJ
I don't think you understand... you don't have to do anything at the pcm. Just do the same resistance measurement on the same "pin pairs" going towards the pcm... don't disconnect at the pcm. The results may tell you that you have broken wires or not... but you can go from there.
Ok Thanks for the info. I"m pretty sure I have a handle on what I need to do (finally). Have a great weekend.
 
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NJTB

Member
Aug 27, 2012
612
Flemington, NJ
A while ago, I had a intermittent C302 code (no output, rear speed sensor) that I chased for a year. Used a Tech 2, all the components on the 4WD could be commanded to operate and the voltages scanned, so I was pretty sure there was no parts needed.
Then I started chasing wires (ohmed them out) and found nothing.
Out of frustration, I took it to the dealer, and $325 later it was fixed. They said on the repair order there was 'rodent chewed wires'. I checked from front to rear and didn't see any repairs, but the Service 4WD light is off, and 4WD works. Go figure.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Maybe they weren't broken but shorted. Check for a dead short between the wire pairs.
 
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jmonica

Original poster
Member
Apr 2, 2013
384
Hamburg, NJ
A while ago, I had a intermittent C302 code (no output, rear speed sensor) that I chased for a year. Used a Tech 2, all the components on the 4WD could be commanded to operate and the voltages scanned, so I was pretty sure there was no parts needed.
Then I started chasing wires (ohmed them out) and found nothing.
Out of frustration, I took it to the dealer, and $325 later it was fixed. They said on the repair order there was 'rodent chewed wires'. I checked from front to rear and didn't see any repairs, but the Service 4WD light is off, and 4WD works. Go figure.
Crazy. Your story kind of worries me as I chase what think may be a broken (or now rodent destroyed) wire some place. I will post what I cam if I do isolate the problem. Sorry it cost you $300+ but at least its fixed. Thanks
 

NJTB

Member
Aug 27, 2012
612
Flemington, NJ
jmonica
I had just hit the point where I knew the repair was past my ability, and didn't want to throw parts at it, not knowing if it was a TCCM or something as expensive. The fact that the components could be commanded told me there were no hard parts needed.
I figured if the dealer told me it was going to cost $1000 that service 4WD light was going to be on a LONG time.
 
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jmonica

Original poster
Member
Apr 2, 2013
384
Hamburg, NJ
Maybe they weren't broken but shorted. Check for a dead short between the wire pairs.
Ok so that problem is solved. After checking the resistance at the PCM to compare to the connector at the sensor, the VSS had reading at the PCM. Exactly what I was hoping it had.

So I start tracing wires, looking for a break. I used the old 50/50 method to narrow it down to the top of bottom half of the harness. It was zeroing in on the wire where I had broken it and repaired it. I went to check that and I disconnected a few connectors to get the wire closer and easier to work on and low and behold, the last connector I pulled out, I just caught a glimpse of the terminals inside. Or I should say "terminal". I could only see one. One of the male terminals was completely bent down inside the connector. I don't even know how that's possible but I knew right away that was the problem and that was it! No more P0502 error, speedo works and its shifting well.

Now I just have a P0443 error but that shouldn't be a big deal. Thank You everyone who helped out with this. I have SO much more to do I am sure I will be posting and lurking here for quite some time. Thanks again!
 

maryserv

Member
Aug 30, 2019
4
TX
OP,
How did you resolve that code? I've resolved a ton of codes and this one is kicking my butt. Replaced the purge solenoid under the hood and the vapor canister solenoid near the gas tank. Checked the fuse. The purge solenoid (new) is not cycling on. Was yours?
 

mrrsm

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Oct 22, 2015
7,639
Tampa Bay Area
How about replacing the Gas Cap with a Brand New ACdelco OEM Only version.. .and then Clear the Code(s) and take it for a Test Drive to see what happens? A Bad Gas Cap can Trigger a P0443... and OTHER Gasoline Vapor Retention EPA Codes, too.
 
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maryserv

Member
Aug 30, 2019
4
TX
How about replacing the Gas Cap with a Brand New ACdelco OEM Only version.. .and then Clear the Code(s) and take it for a Test Drive to see what happens? A Bad Gas Cap can Trigger a P0443... and OTHER Gasoline Vapor Retention EPA Codes, too.
Gas cap was the very first thing I did, however I didn't do a ACDelco OEM. Will that really make a difference?
 

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