V1 Cobalt related No-Crank

[Trail_Creeper]

So I had the car running, found out the alternator was dead. Yesterday changed the alternator and put in a junkyard lower fuse box to hold the fuse panel and ECU (mine was missing)... now it won't crank.

Key in "on" position and everything comes on (stereo, horn, blinkers, etc). But the car won't crank and OBD-II port wont read.

Went out this morning and re-seated all the BCM and ECU plugs same issue. Did some searching on the Cobalt forums and found some things to check out after work like grounds. Since you all have taken these apart and had your own sets of issues I figured I'd ask here.

 

[OptimizePrime]

Does your gas gauge go to the right level with the key in 'On' ?

Sounds like Data wire connection.

 

[Ross]

The gmlan needs data flowing to allow the engine to crank. So if your obdii port isn't communicating, that needs to be fixed first. You might be able to start it if you put the key in the run position, and jump the starter. For a Goblin, the ECU/TCU passes data to the power steering unit, the BCM, then the obdii port.

 

[Gtstorey]

Check and see if you have voltage to the OBDII port. Might have a loose connection on a pin on one of the fuse box connectors. I assume you confirmed that all of the fuse block connectors were screwed on tight?

 

[Trail_Creeper]

Does your gas gauge go to the right level with the key in 'On' ?

Sounds like Data wire connection.

I'll have to check. I believe it was reading correctly.

The gmlan needs data flowing to allow the engine to crank. So if your obdii port isn't communicating, that needs to be fixed first. You might be able to start it if you put the key in the run position, and jump the starter. For a Goblin, the ECU/TCU passes data to the power steering unit, the BCM, then the obdii port.

And that's the odd thing, when it ran the other day I had no issues. OBD port worked, car drove fine, no issues at all... until the battery died from the alternator not charging.

Check and see if you have voltage to the OBDII port. Might have a loose connection on a pin on one of the fuse box connectors. I assume you confirmed that all of the fuse block connectors were screwed on tight?

They are all screwed in. I'm guessing that everything is getting power, but won't know for sure until I break out the multimeter.

 

[Chubbs]

Are all the wires on the starter solenoid hooked up right? It's been a while since I looked at it, but I thought the alternator wire went to the solenoid. If you had to unhook it to replace it, maybe it didn't go back on right.

Before troubleshooting data connections, I would just put 12v to the starter solenoid and see it cranks. If it does, then you can start figuring out why the key isn't getting 12v to it.

 

[Trail_Creeper]

Are all the wires on the starter solenoid hooked up right? It's been a while since I looked at it, but I thought the alternator wire went to the solenoid. If you had to unhook it to replace it, maybe it didn't go back on right.

Before troubleshooting data connections, I would just put 12v to the starter solenoid and see it cranks. If it does, then you can start figuring out why the key isn't getting 12v to it.

I've got power all the way to the alternator. So I believe that is good. Going to dig into it shortly... after I get back to the house

 

[Trail_Creeper]

Everything in the Fuse box, and OBD port is getting 12v. ECM still isn't talking to the OBD port. Currently working my way to from the Fuse box to the ECU checking grounds and power.... something just isn't adding up with it.

 

[Trail_Creeper]

Have continuity to ECU for power, but no power

 

[Gtstorey]

Have you pulled the wiring diagrams for your Donor?

 

[Trail_Creeper]

I've found them using Google. Looking at the what I've found J1 pin 56 should be a ground and it has no continuity, so now I need to figure out where that wire runs.

 

[Gtstorey]

Ross has posted his aldata subscription for the 2006 SS/SC.

 

[Trail_Creeper]

Thanks to @Ross for the use of his AllData subscription!

But, I'm officially stumped and need a sanity check. With power "on" the Powertrain relay should close and provide power to the Emission 10a, Injector/Ignition mod 10a, and ECM/PCM 15a fuses, correct?

Because as of right now I'm jot getting power to any of those even after swapping the Relay with the Run/Crank next to it.

From what I'm seeing is the powertrain relay isn't getting power, nor is it "switching" to provide power to the ECM which shooould result in my issues.

Anyone sane to check me is greatly appreciated.

 

[Gtstorey]

You should be getting power on 2 of the 4 terminals of that powertrain relay plus a switched ground (probably controlled by the BCM, but don't remember that for sure) and the load. There should be a more dedicated schematic that will detail it out. Remember that the relay works off the diagonals for the control side as one diagonal and the load side as the other. I think that no power to any pin is a failure in the circuit board within the fuse box, but need to see the dedicated schematic to confirm.

 

[Trail_Creeper]

Appreciate the info. I'll see if I can locate something if I get time at work tonight.

 

[Gtstorey]

You can get to the fuse box circuit board by removing the all of the fuses/relays from the top and the connectors on the bottom if you get to that being the issue. You can then check continuity and try and figure out where it's broken. Again I'm not sure that both feeds are off the circuit board, but that is what the diagram you posted indicates. The schematics for the later models are done a little different and are more clear on what is happening. If it isn't getting power from the circuit board, I think it will have pins for the bottom wire connectors directly in line with the relay pins (a straight through connection).

 

[Ark :D]

When I had the exact same no-crank condition, the problem ended up being the little metal tabs inside the fuse box connectors. I had completely run out of other options, so I opened up the fuse box and cleaned up all (as well as re-bent some) of those connectors. After I closed it back up, everything was good.

Just adding something to consider.

 

[Gtstorey]

When I had the exact same no-crank condition, the problem ended up being the little metal tabs inside the fuse box connectors. I had completely run out of other options, so I opened up the fuse box and cleaned up all (as well as re-bent some) of those connectors. After I closed it back up, everything was good.

Just adding something to consider.

I had to do the same thing on mine, fixed several issues at once. Just need to determine whether that relay is fed off the board or by individual wires.

 

[Gtstorey]

I checked the diagram for the newer cobalts and the power train relay has 2 pins fed from the B+ bus which is the circuit board fed from the B+/jumper post on the side of the fuse box. Yours is probably the same and if you have power on the “post” you have a problem with the circuit board. Assuming you were checking for voltage to a good ground.

 

[Trail_Creeper]

Got out of work early today. Here's to hoping I've found the problem...