Prndl going crazy

#1
a 2005 GMC envoy xl Denali. I purchased it a few months ago and has been fantastic until a few days ago. In park it runs great and has no issues. When put in gear and after driving a mile or 2 the prndl jumps from what ever gear you are in to park and back, rapidly until you shut it off for a few hours. It's not a cluster problem. The trans is actually shifting. It is full on fluid and recently had the shift cable replaced. Replaced battery also. Please help
 

MRRSM

Lifetime VIP Supporter
#2
There is an excellent clue here that is easily investigated...but requires a hopefully memorable analogy: A Bicycle Handbrake. If the Cable Housing becomes unscrewed in front of the Handle Bracket... The Hand Brake gets loose enough for the Cable Swaged Ball to slip out and the Brake becomes useless. Like this Handbrake Example... when the Shift Cable was replaced... it was necessary to fit the Housing end into a Bracket mounted on the Driver's rear side of the Transmission Housing...and the expanded Black Plastic End is supposed to be held in place by a Large "Staple" that slips through the Cable Housing and The Holding Bracket.

The two Razor Sharp Points get pushed up through the two rectangular Bracket Slots and bent over the top of the Holding Bracket to keep the Cable Housing held firmly in place. This allows the internal Cable to slide freely in and out by the action of the Shift Handle through the PRNDL cycle, moving the cable and by proxy... the Shift Lever on the 4L60E Transmission. If the Staple falls out... The Housing can and often will..."Jump The Track"...making the Shifts from inside of the vehicle ...unreliable.

This can be easily investigated by observing the Driver's underside of the Transmission with a Bright Flashlight and checking the Cable/Holding Bracket relationship for looseness... and a Missing Staple. If you cannot find a replacement... you can still secure that location using a length of 0.041" Safety Wire and re-fasten these items firmly in place. If you find no problems with the Cable Housing and Bracket... find out from the Mechanic if he mistakenly decided to remove the Park Neutral Switch and improperly re-installed it when he was also attaching the New Nylon Cable Connector to the 4L60E Shift Armature.

The last aspect here is that if your OEM P-N-S is NOT FUBARed... it might still require the adjustment of its position by loosening the two P-N-S Bracket Bolts and re-aligning the New Cable length to be consummate with the ACTUAL position the Shift Handle and PRNDL are in to match the need to ensure that the Transmission's internal gearing position actually is in Park or Neutral and WILL NOT ACCIDENTALLY MOVE WHEN TURNING THE KEY AND STARTING THE ENGINE.
 
OP
OP
Spck

Spck

Member
#3
Thank you for your insight. The cable was adjusted properly, with the retainer staple. The pns was not removed. The shifter stays where it is supposed to and the trans acts normal until it starts to slightly warm up. The display bounces around and I can hear the trans moving internally
 

budwich

Well-Known Member
#4
But I think you are looking at only the "mechanicals of shifting".... there is also an electrical portion to the system. Much like the gas pedal which has no direct link to the throttle body and relies on the pcm to move it, it is also quite likely that portions of the transmission operation do not necessarily "lock" the transmission mechanically with the gear shift... meaning that if the pcm detects a shifter change, it does a shift change. Likely first place to look is at failed / failing transmission range switch and go from there.
 

MRRSM

Lifetime VIP Supporter
#6
The Two Wire Connector Bundles fitted into the back of the P-N-S may have a broken or separating wire inside with occasional close contact making the signalling between the PNS to the PCM an 'On and Off' situation. You could inspect the wire bundles ...and even move them around and then Test Drive the vehicle to see if anything improves. If the problem disappears... then you will need to do check of the Colors and Locations of the Low Voltage Signal wires in one or both Connectors and trace any breaks. On the receiving end... there have been instances where wires inside of the PCM Three Main Connectors will suffer breaks-frays that could be involved. Here is a Wiring Diagram of that Circuit:

2012-03-03_142232_1.gif

... and if you need to Wire Trace all three Wire Bundle Pin-Outs to and from the PCM... Check out and download the many images in Post #4 at this GMTN link:

https://gmtnation.com/forums/threads/bcm-pinout.16994/#post-533371
 
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budwich

Well-Known Member
#7
I don't believe your issue is with the PNS as you aren't having starting issues. You need to pull the diagram of the range switch / transmission selector and see what it tells. The sensors are pretty simple and in most case are just resistances that allows the PCM to determine what gear the system "thinks" has been selected.... note the "selected" part... as opposed to which gear the engine "wants to run in".
 
OP
OP
Spck

Spck

Member
#8
I don't believe your issue is with the PNS as you aren't having starting issues. You need to pull the diagram of the range switch / transmission selector and see what it tells. The sensors are pretty simple and in most case are just resistances that allows the PCM to determine what gear the system "thinks" has been selected.... note the "selected" part... as opposed to which gear the engine "wants to run in".
So which direction would you point me in?
 

budwich

Well-Known Member
#10
I see that the range selector switch IS part of the PNS switch so indeed you need to look at the switch which basically is and open and closed type continuity on the wiring pins based on what is selected... so you should see that happening when you move the selector and measure the outputs. You might have to physically inspect the switch to see what its integrity is like.

It appears to be bolted externally to tranny so replacement is probably easy assuming that's the problem...BUT there are other potentials, hence you need to do one step at a time or "one part at a time". Further it could be as simple as loose wiring.
 
#11
A possibility is that the PRND indicator itself is defective or the cluster is. The indicator is controlled by a circuit in the cluster, same as all the other lights and gauges. Another possibility is something on the data bus is sending bad info to the cluster. I'd get a Bluetooth OBD adapter and use the Torque app to read what transmission position is detected.
 

budwich

Well-Known Member
#12
Odds are slim that it is actually the PNS switch itself. It is more likely a connection to the switch and probably the ground which might be "flapping in the wind" causing the PCM to think things are being shifted.
 

budwich

Well-Known Member
#14
back up to original description, you appear to indicate that you are driving down the road (ie. moving) and then the shift indicators start moving AND the tranny starts shift to "park"... not sure what gear that is... no gear? does your vehicle actually stop moving?

lastly, does this happen with all gear choices or just "D".... ie. what happens if you use "3"?
 
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budwich

Well-Known Member
#17
hmmm... that's sound rather "funny"... what do mean about the "loses power"... revs drop, engine revs but speed doesn't increase / drops. It would appear that the "shifts to park" means "no gear... but also doesn't cause the park prawl to activate which is more mechanical than electrical.

I guess another question is have you scanned for codes, pending or otherwise?

with the new information, I am thinking a PCM fault.
 

budwich

Well-Known Member
#20
OK... but what's the check engine light on for? I don't see any rev changes so what are you referring to with "loss of power".
 
OP
OP
Spck
#21
MIL for o2 sensor bank 2 sensor 1. It does drop rpms more noticeable in higher gears. Starting from a stop seems to be in 2nd intermittently. Will randomly drive perfect for a few minutes at a time
 

budwich

Well-Known Member
#22
But that is also strange... because if the tranny is truly shift to something... especially from higher gear to lower (assuming its at the highest to begin the "flicker") then rev's should go up.

what are reading / scanning the check engine with? Are you sure you are seeing ALL the codes?

besides the fuel low what other warnings are on the dic?
 
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xavierny25

Well-Known Member
#23
I'm also seeing the abs and brake warning lights are on. Did that also come along after the gear indicator started going bonkers?
 
OP
OP
Spck
#24
Snap on Solus ultra. No trans codes. And Trac lights come on when first starts acting up and goes away after a few miles. Shows stored codes for all 4 wss
 

budwich

Well-Known Member
#25
can you post a picture of the PNS switch part that you replaced (ie. the old one).... just to make sure we are on the same page as my reads seem to be unclear in this area. Maybe mrrsm post about the mode select isn't so far off... :smile:
 

budwich

Well-Known Member
#27
Interesting... I haven't actually crawled under to look at mine (yet). Anyways, am I seeing correctly that the electrical portion of the "switch" was not replaced (ie. "re-use" of the old range module)?

oops... i see what you are saying, its the same look with and without the switch.
 
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budwich

Well-Known Member
#28
As suggested by someone, can you monitor the PID for the tranny gear?

Can you check the black wire going to the switch to see if it is grounded well (measure with a resistance meter to a KNOWN ground).
 
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Mike534x

Well-Known Member
#29
I wonder, but could there be a possibility that the issue lies in the Transmission Control Module, since he has the 5.3 it sits behind the PCM near the Power Steering Pump. I'm not sure what the odds are that it could be it, but it wouldn't hurt to pull the housing out and inspecting the connectors and gaskets.
 
OP
OP
Spck
#30
Thank you all so much. I will check everything out in the morning when I get to work. I left the vehicle there. I cleaned all 3 grounds on the left side of the block, 5 body grounds in the engine compartment. Even replaced some eyelets that didn't look so great. Still no luck. I'll look up schematics in the morning and start ohming the wiring.
 

MRRSM

Lifetime VIP Supporter
#31
Unless you've already viewed this TV Thread... the OP's experience over there seems parallel to your issues... and replacing the PCM in his vehicle seemed to do the trick:

https://forums.trailvoy.com/archive/index.php/t-78784.html

EDIT:

Thanks to @Mooseman 's refinement in Post #33 correcting this suggested solution as being the TCM R&R vs. it being the PCM. 'Preeshiate That!
 
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budwich

Well-Known Member
#32
I am fearful that might be the only answer "pcm replacement". The PCM has a look up table which tells it what the switches mean. The question is, is there anything that "triggers" the lookup OR is it a "scheduled" function (ie. every x msec). If it has no trigger and goes purely on the lookup and the lookup result is different, it just follows that blindly and starts changing things.... maybe. It doesn't sound quite right... as then I would think perhaps the PCM would be more bonkers... but you never know. Having said that the OP indicates other PCM "fault codes" which may indicate more problems with the PCM as it is hard to believe all WSS sensors are bad.

There is also some other components, which read gearing, internal to the tranny and feed that information outward.... but this is way beyond me.

To me the issue is more electrical than mechanical since stop and starting the engine gets some relief. Further, there is still some question around... did some work with the shift cable and now there is this problem... BUT I don't think I have seen a well defined "timeline" to "work done" things were this way and then things went this way days later... or whatever it actually was.

I almost get the feeling that the "cable change" was done as a first attempt at resolving this problem.... which it didn't. Then the switch was changed and that had no impact.

That's just my read though... OP needs to qualify things a bit.
 
#33
In that TV thread, it indicated the Transmission Control Module (TCM) as the cause, not the PCM. Since this is a 5.3, they are separate modules.

@Spck , to avoid overinflated costs at the dealer, try to find a used TCM for the same year truck/engine and swap it in. It shouldn't need any programming or security relearn.
 
OP
OP
Spck
#34
Thank you so much. Read the other thread and sounds exactly like what I'm experiencing. Have a tcm on order, will be in tomorrow morning.
On a related side note, seems to have a slightly different reaction every time I unplugged and plugged back in the tcm. Hopefully will correct my issue. I'm a Chrysler tech and have 2 other higher up techs helping me, neither have seen anything like this before.
 

MRRSM

Lifetime VIP Supporter
#35
Post #36 in this Thread has a very Useful TCM Wiring Pinout Diagram if you need to probe any of the Harness Wires and Connectors... you can ignore most of the text as it primarily covers trying to isolate the means to connect a "GYMKO" Bench-Top Test Harness I am working on and a Tech 2 up to the TCM for Complete Off The Vehicle Diagnostics:

https://gmtnation.com/forums/thread...h-2-bench-top-test-harness.18272/#post-553239


BESTTCMWIREDIAGRAM.jpg
 
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OP
OP
Spck
#36
I am fearful that might be the only answer "pcm replacement". The PCM has a look up table which tells it what the switches mean. The question is, is there anything that "triggers" the lookup OR is it a "scheduled" function (ie. every x msec). If it has no trigger and goes purely on the lookup and the lookup result is different, it just follows that blindly and starts changing things.... maybe. It doesn't sound quite right... as then I would think perhaps the PCM would be more bonkers... but you never know. Having said that the OP indicates other PCM "fault codes" which may indicate more problems with the PCM as it is hard to believe all WSS sensors are bad.

There is also some other components, which read gearing, internal to the tranny and feed that information outward.... but this is way beyond me.

To me the issue is more electrical than mechanical since stop and starting the engine gets some relief. Further, there is still some question around... did some work with the shift cable and now there is this problem... BUT I don't think I have seen a well defined "timeline" to "work done" things were this way and then things went this way days later... or whatever it actually was.

I almost get the feeling that the "cable change" was done as a first attempt at resolving this problem.... which it didn't. Then the switch was changed and that had no impact.

That's just my read though... OP needs to qualify things a bit.
Trans shift bushing Went bad. Tried to replace it and broke the cable. Replaced the cable and everything was fine for 3 weeks.
Then it started acting up. Replaced the pnp on a whim with no luck. Have checked all fuses and circuits wall seem to be fine. Replaced ignition switch because of a related thread, no luck. Checked cluster power, grounds and signal. All good. Cleared all codes and only have a transfer case motor code and rear abs code. Plugged in snap on Solus ultra and tcm keeps dropping out. Checked powers grounds and ignition circuits again. All good. Ordered tcm from dealership based on known info and previous reply. Will update as soon as I know a positive repair or failure
 

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