V1 ECU not connecting to OBDII and coolant temperature fluctuating

[KingChuck24]

Hello everyone,

I recently pulled the engine out of my car and trimmed down the engine harness as well as rewrapped some parts. While doing so I must have either knocked something loose out of its socket or cut an incorrect wire.

Currently the car is running and driving but the engine does not feel right and on top of that the coolant temperature reading on the dash when in neutral sits at 106 and when I drive the car it jumps around from as low as 30 all the way to 300. When I plug in my scanner I cannot get it to read the ECU at all and it wont connect to the car.

I tried looking for some things on my own and testing the grounds by the engine which all checked out. I checked the pins on the C101 connector which from what I gathered carries the GMLAN connection from the ECU up to the BCM and those checked out.

Has anyone else ever had this issue?

I'm going to keep trying over the next couple of days to get this fixed but my planned track day this coming Wednesday might need to be canceled.

 

[KingChuck24]

Also I forgot to mention when I unplug the coolant temperature sensor plug, the reading at idle stays at 106 and does not change even if I plug it back in. This leads me to believe its something further down the line with the CAN system.

 

[Ross]

Maybe the connectors? Check the rear fuse box and see if all the 7mm bolts are snugged up on the lower connectors. Maybe loosen them, then reseat them. Same on the BCM.

 

[KingChuck24]

Tried that and no luck. Just going through right now and testing different circuits and making sure I have continuity.

 

[KingChuck24]

So I was just going through some more stuff and decided to look closer at my coolant temperature sensor and I figured out that instead of being connected at pin 55 like the diagram says my wire is yellow wire is connected to pin 66 which makes no sense to me as the diagram says that pin is unused.

Could this be a product of the aftermarket supercharger kit? Does the factory supercharged car have this pin being used for ECT? I don't have access to the 2.2l engine so I can't figure it out.

I have a different wire in pin 55 that is also yellow but it does not connect to the ECT. Currently I do not know where it goes and I am going to look right now to see where it leads to.

 

[Gtstorey]

You can't use mix wiring diagrams from one ECM to another or one model to another.

 

[Gtstorey]

links to other service manuals are available here (maybe, I haven't used the link).

Service Manuals

Just got this link from a buddy of mine. Looks like a pretty complete set of service manuals that cover all years and trims of the Cobalts, as well as other vehicles. https://charm.li/

dfkitcar.com

 

[KingChuck24]

Thank you for that link, didn't realize that was out there.

I looked through the 2.0 and 2.2 and neither of them had what I was looking for. Only thing I saw was on C2 for the 2.2 on pin 66 was the crank position sensor but I know that makes no sense for my setup.

I just do not understand how my coolant temperature could have been working on pin 66 and 67 before but now it is not. I would think that there would be an issue from the begging of having it on those pins.

I think at this point I might just run the car until it breaks on track and then after that its the end of the season. I was already planning on building the engine but I might move that money to go to a standalone ECU like a Haltech.

 

[Robinjo]

Maybe you have a break in those wires?

 

[KingChuck24]

I checked continuity between the C3 pins and the actual connector pins and they were good. I then plugged in the sensor and tested continuity between both of the pins on the C3 connector and it gave me continuity with some resistance which makes sense.

 

[Robinjo]

I checked continuity between the C3 pins and the actual connector pins and they were good. I then plugged in the sensor and tested continuity between both of the pins on the C3 connector and it gave me continuity with some resistance which makes sense.

You could also check resistance with the sensor hot and cold to see if it changes. I don't think it's the sensor but I would check that before diving into the harness and all that.