04 GP Shift indicator erratic!

[99z34na]

04 GP GTP.  The DIC screen shows mileage and the shift position.  However the position it reads is going all over between 1 2 3 P D crazy like while driving or sitting.  Also the shift between 1-2 is like getting shoved from behind harsh.  Checked the pcm and what wires I can get at, checked battery and cables, unplugged and replugged DIC.   Going to look at the Neutral Safety Switch and the plug on the Transmission.  
 

never seen anything like this before.   Also it doesn’t always want to start at all.  Like no crank at all.  This is why I’m hoping the Neutral Safety Switch.  
 

any expertise????

[Black92GS]

51 minutes ago, 99z34na said:

04 GP GTP.  The DIC screen shows mileage and the shift position.  However the position it reads is going all over between 1 2 3 P D crazy like while driving or sitting.  Also the shift between 1-2 is like getting shoved from behind harsh.  Checked the pcm and what wires I can get at, checked battery and cables, unplugged and replugged DIC.   Going to look at the Neutral Safety Switch and the plug on the Transmission.  
 

never seen anything like this before.   Also it doesn’t always want to start at all.  Like no crank at all.  This is why I’m hoping the Neutral Safety Switch.  
 

any expertise????

Before you change the range sensor, double check that you don’t have any chafed wiring, corroded pins in the connector etc… first. Don’t want to replace it if there is something else at play. 
 

I can just about guarantee that your no starts and rough shifts are all related, so I wouldn’t worry about those until you get the range sensor issue worked out. 

[55trucker]

You did say that your car is an '04?

The range selector switch/neutral safety switch is internal on an '04 model. It's not mounted to the outside of the case.

[99z34na]

Yes it’s an 04.  And oddly I am not finding the usual YouTube school of fixin’ videos.  Is it a drop the pan kinda job?

 

I’ll be under there next week with some scrutiny and a flashlight.  I got some codes last week that were concerning too.  That’s why I started with the PCM inspection.  

[99z34na]

[99z34na]

These were the codes I got when the shifting became very harsh.  

[55trucker]

That PO742 doesn't sound, if indeed the TCC is locked due to a fault in either the electronic circuitry, the solenoid passage is mechanically gummed up or the clutch is mechanically locked that'll have a severe effect on the engines ability to try to turn over. If in either Park or Neutral & one tries to start the engine if the torque converter isn't releasing the engine will stall near instantly.

In effect the converter is locked up & the converter turbine & impeller will not spin freely of each other. Lock up should only occur in O/D,D & 3rd. 

Yes, one has to pull the trans side cover to get at the range selector. That may mean pulling the trans from the car.

  

Edited yesterday at 09:20 PM by 55trucker

[99z34na]

2 hours ago, 55trucker said:

That PO742 doesn't sound, if indeed the TCC is locked due to a fault in either the electronic circuitry, the solenoid passage is mechanically gummed up or the clutch is mechanically locked that'll have a severe effect on the engines ability to try to turn over. If in either Park or Neutral & one tries to start the engine if the torque converter isn't releasing the engine will stall near instantly.

In effect the converter is locked up & the converter turbine & impeller will not spin freely of each other. Lock up should only occur in O/D,D & 3rd. 

Yes, one has to pull the trans side cover to get at the range selector. That may mean pulling the trans from the car.

 

2 hours ago, 55trucker said:

  It’s only not started once and it was a no starter situation.  Like nothing, not a click or nothing.  We did hear fuel pump tho.  We wiggled the shifter a bunch and it finally started.  It drives normally until it’s warm.  Then the harsh shifts start.  And the fluctuating drive indicator on the DIC has me thinking it’s still electric and not a mechanical failure.  
 

I sure would like to not drop the transmission since I’ve never done it to a fwd car.  I’ve done the motor mounts and the steering rack twice so I’m familiar with the subframe below somewhat.  

[55trucker]

Let's start here..........what are you using as a scanner?

Is it dedicated OBD2 scanner such as a Matco/Snap-on/OTC?

Is it a laptop with a scanner program loaded onto the laptop?

You want to clear all of those codes, start & run the car in *real time* (the laptop/scanner connected) & drive until those codes reappear.

They're going to be either soft codes or hard codes. Hard codes will not clear until the problem(s) have been solved.

Soft codes usually clear after a number of ignition key/engine run cycles & the PCM corrects.

[99z34na]

My scanner is a WiFi iPhone scanner.  It is mostly read only.  I could dig deeper into its live reading but all I’ve ever monitored was misfires and temps and very simple PIDs.  Unfortunately that level of scanner is the only one in my budget.  I agree live data would be helpful.  
 

Last week after the first check engine light that included p0651 I cleared all codes and forgot about it and hoped it was a fluke (I can dream).  

And then when it started doing the shifting problem I had no CEL and only read codes for the sake of it.  I cleared the second set of codes and hoped it was the heavy rain that day.  (Seriously a big dreamer here) that was the P0742 the first time I believe

the last set of codes was after checking the connections at the PCM and DIC and cleaning up the battery connections for good measure.   There was still no CEL on the dash.  We drove it up the frontage road and back as soon as it shifted hard between 1-2

 

thanks for the ongoing help.   I’ll have much better info when I can get in there more.   Currently not able to work on it due to work.   
 

 

 

[Black92GS]

After seeing the code list, my thoughts are now that you're either going to be dealing with a bad sensor somewhere on the 5 volt reference B side possibly shorting out internally and taking down everything else, a chafed wire or corroded connector somewhere.....or even a failed PCM. I would ignore the harsh shifting and random no-start at this time, since those are likely just symptoms of the overall issue.  

5 volt sensors generally work based on a voltage output to represent a particular value.  Take your range sensor.  It would receive a 5 volt signal, and would output a different voltage to represent PRND321. If the 5 volt signal going into the sensor is being pulled down slightly and randomly by something else, the output voltage will change, and the PCM can interpret those changes as different reported shifter positions. If the vehicle is off and its reporting something other than park or neutral....it won't start. It may also begin shifting funny as it no longer knows which position the shifter is in. 

If it were me...I'd be starting my troubleshooting on that 5 volt reference branch first. 

[99z34na]

Thanks Black92GS, I’ll get a wiring diagram and start tracing anything I can.   Today I had an hour to check and even cleaned all fuse connections in both boxes.   Nothing looked out of the ordinary.  

After I hooked the battery up again I tried a start and had crank for 1 second and then completely dead again.   Locks windows lights etc all work normally.  So I put my head under the hood and hit the remote start to listen.   Everything seems to power up and then after a couple seconds you hear the drop in voltage when the starter would engage but nothing.   Then as it cycles and tries again I hear the little clicks and chirps coming from the transmission.   It tries three times and nothing.   
 

shift selector still says wrong gear (mostly 3) and there’s some more random codes my reader can’t detail.   Says something like only available with add on from GM.  
 

tried one more time with the remote start while wiggling any harnesses I could get at from above and no changes or surprises.   
 

I'm close to letting a professional look at it but I’m afraid they are going to take weeks to find the gremlins.   Pretty discouraging feeling today so I’m going to the mountains for 4 days in the suburban to listen to a bunch of bluegrass and drink myself happy.   I’ll keep this updated as it progresses next week.