P0976 question

[skynyrdcat]

i HAVE THE DREADED 976 on an 07 cobalt 2.2.

When I check the trans fuse in the engine compartment I have 11.3v on one side ans 1.7v on the other side.

I assume that it's a short since it's hot on both sides, just wanted to get some other opinions on it.

Thanks in advance.

 

[cobalt123]

bump

 

[Tuner923]

i HAVE THE DREADED 976 on an 07 cobalt 2.2.

When I check the trans fuse in the engine compartment I have 11.3v on one side ans 1.7v on the other side.

I assume that it's a short since it's hot on both sides, just wanted to get some other opinions on it.

Thanks in advance.

not necessarily a short...

there's not really a lot of info to go from here.. so

now If you are talking about some voltage on the ground after the "load" that is a sign of high resistance on the ground wire. more than likely meaning that there is a bad/corroded connector or the mount to ground is corroded or possible the ground wire is frayed or pinched...

how are you checking this.. where are you placing each lead of the meter? I really hope you are using a digital meter and not an analog voltmeter.

 

[skynyrdcat]

not necessarily a short...

there's not really a lot of info to go from here.. so

now If you are talking about some voltage on the ground after the "load" that is a sign of high resistance on the ground wire. more than likely meaning that there is a bad/corroded connector or the mount to ground is corroded or possible the ground wire is frayed or pinched...

how are you checking this.. where are you placing each lead of the meter? I really hope you are using a digital meter and not an analog voltmeter.

Digital yes.

I removed the trans fuse, put the blk dmm lead on the neg battery post and put the red on either fuse terminal. I have voltage on both terminals less than 12 on the IN side and over one on the OUT or trans side

 

[Tuner923]

I'd say next place to look is all wiring to the 2-3 Shift Solenoid

 

[skynyrdcat]

If I'm getting less than 12 to the fuse could that be the problem? The TCM is supposed to give ignition voltage to the 1-2 and 2-3 solenoids, and control them by providing a ground path for either. Ignition voltage would be 12.5v right?
I found where the harness was rubbing the corner of the bell housing and fixed it, so I only have power on the input side of the fuse now, but still less than ign voltage (11.7 now) would that be enough to trigger the codes / no shift?

I plan to check the TCM harness for voltage on the #2 (1-2 solenoid), #31 (ign voltage from fuse) and #20 (2-3 solenoid) wires, as soon as weather and time permit. But, if I only have 11.7 going to the TCM, I don't think I'd expect to see 12.5 going to the solenoids.
Any thoughts?
Assuming I find 11.7 going to the solenoids, should I try a fused jumper from bat + to the #31 wire?

 

[Tuner923]

If I'm getting less than 12 to the fuse could that be the problem? The TCM is supposed to give ignition voltage to the 1-2 and 2-3 solenoids, and control them by providing a ground path for either. Ignition voltage would be 12.5v right?
I found where the harness was rubbing the corner of the bell housing and fixed it, so I only have power on the input side of the fuse now, but still less than ign voltage (11.7 now) would that be enough to trigger the codes / no shift?

I plan to check the TCM harness for voltage on the #2 (1-2 solenoid), #31 (ign voltage from fuse) and #20 (2-3 solenoid) wires, as soon as weather and time permit. But, if I only have 11.7 going to the TCM, I don't think I'd expect to see 12.5 going to the solenoids.
Any thoughts?
Assuming I find 11.7 going to the solenoids, should I try a fused jumper from bat + to the #31 wire?

so you found a short on the wire to ground? Has the code gone away since finding the wire rubbing on the bell housing. That would cause a low voltage at the solenoid.

I meant to go into all data and shop key today but it slipped my mind today. I am going to set a reminder on my phone and print out a bunch of the wiring diagrams and related info. it's kinda hard to do this without it in front of me.

Jumper wires are intended to find an open in a circuit. but if fuse os the same amp rating or lower should be safe

out of curiosity what is your battery voltage KOEO? If it's 11.7v it would explain why you are not getting 12.5v at the fuse.

 

[skynyrdcat]

so you found a short on the wire to ground? Has the code gone away since finding the wire rubbing on the bell housing. That would cause a low voltage at the solenoid.

I meant to go into all data and shop key today but it slipped my mind today. I am going to set a reminder on my phone and print out a bunch of the wiring diagrams and related info. it's kinda hard to do this without it in front of me.

Jumper wires are intended to find an open in a circuit. but if fuse os the same amp rating or lower should be safe

out of curiosity what is your battery voltage KOEO? If it's 11.7v it would explain why you are not getting 12.5v at the fuse.

Some of the all data stuff doesn't line up... Some diagrams show the circut with a 15a fuse, some show it with 10, etc and one diagram will show RD/WH wire color and the next show a different color.

I'll check the battery voltage when I get home. I think I checked it but didn't pay much attention because it was normal. If it had been low I'd have taken notice.
Anyway, more info to come this evening.

 

[skynyrdcat]

Battery voltage 12.0.

IGN to TCM 11.8

TCM to 1-2 solenoid = .2v

TCM to 2-3 solenoid = .3v

I'm thinkin the TCM is shot. It should have ignition voltage to both solenoids with the key on, and then ground one of them accordingly. If I have power to the TCM and none coming out, I think that constitutes springing the $50 for a TCM.

 

[YelloEye]

I assume you have the wiring schematic in front of you?

If not it's worth it to get the service books and or have someone else take the same readings on their car.

 

[skynyrdcat]

I assume you have the wiring schematic in front of you?

If not it's worth it to get the service books and or have someone else take the same readings on their car.

All data DIY

 

[YelloEye]

Is definetly do one of the above before dropping $50 on a BCM.

 

[Tuner923]

Is definetly do one of the above before dropping $50 on a BCM.

All Data is a digital database technicians use, basically every service manual for every car accessed on computer... also allows access to TSBs and recalls ect..

Terry,

I have looked up the DTC P0976 and found that it is triggered when the TCM detects a short to ground. The reading of 1.3v I am assuming that was a -1.3v meaning a short to ground. You indicated that you found the wiring harness to be rubbing on the bell housing and after having fixed this it solved the voltage reading on the load side of the fuse. From here have you cleared the code? if yes has it reappeared? If it has reappeared I would start diagnosis on the solenoid to see if it have an internal short to ground.

 

[YelloEye]

All Data is a digital database technicians use, basically every service manual for every car accessed on computer... also allows access to TSBs and recalls ect..

Nice, I wish I could access that from home. I can only access it at the library.

 

[Tuner923]

Nice, I wish I could access that from home. I can only access it at the library.

I access it at school that and Shop Key.

 

[skynyrdcat]

All Data is a digital database technicians use, basically every service manual for every car accessed on computer... also allows access to TSBs and recalls ect..

Terry,

I have looked up the DTC P0976 and found that it is triggered when the TCM detects a short to ground. The reading of 1.3v I am assuming that was a -1.3v meaning a short to ground. You indicated that you found the wiring harness to be rubbing on the bell housing and after having fixed this it solved the voltage reading on the load side of the fuse. From here have you cleared the code? if yes has it reappeared? If it has reappeared I would start diagnosis on the solenoid to see if it have an internal short to ground.

Yes and no. Actually, I was reading the diagram wrong (the all data tcm diagram is backwards to how it actually lines up in the vehicle). Fortunately the plug has the 1 and 37 wires labeled so I was able to work backward from there. I originally thought the TCM sent power to the solenoids and commanded a ground via the the trans case. However the power goes straight from the fuse block, thru the solenoids and back to the TCM. The TCM then commands a ground inside the TCM.
Disregarding everything mentioned in earlier posts...
The problem turned out to be the ign wire going into the trans. When I unplugged the harness from the trans housing, the male terminal on the trans side was still inside the female terminal on the engine side, and it was slightly black around it. This is the wire that give ign voltage to the 1-2, 3-4 and TCC (I got the TCC P2764 code too).

THE MORAL OF THE STORY... Don't use a test light/ meter to test voltage by probing the insulation on the back side of the connector. Unplug it and make sure you have power to the terminal end!!!!!!

I still haven't repaired it yet, I've got to figure out how to the the trans side connector out. It looks like the connector releases to the inside, so I'll probably be taking the side pan off.

For future reference, if you get a p0976, check for power to the trans fuse in the block, check the fuse itself and if those are good check the number 2 and number 20 wires on the TCM for ignition voltage. If it's not there, the circuit is open somewhere between the trans fuse to solenoid and the solenoid to TCM wiring.
Same thing for the p2764 except it will be the #1 wire on the TCM connector.

Now to figure out if i've got to pull the side cover