Rick's Free Auto Repair Advice

Chevrolet Cobalt No Start

Diagnose Cobalt No Start

Shops are reporting a difficult to diagnose problem with a Cobalt No Start condition on the vehicles listed below that’s caused by a failed module on the data bus or a corroded fuse. When a module shorts, it takes down the entire communication bus and makes it impossible to communicate with the scan tool.

The symptom appears as a no crank. That makes sense since the start relay can’t receive ground from the ECM or BCM if the communication circuit is down or the fuse is corroded.

Cobalt models affected with this problem

2005 – 2010 Chevrolet Cobalt 2.2
2005 – 2010 Chevrolet Cobalt 2.0
2006 – 2008 Chevrolet Cobalt 2.4
2007 – 2010 Pontiac G5 2.2
2007 – 2008 Pontiac G5 2.4

Diagnose Cobalt No Start by checking the fuse

Turn the key to the RUN position. The check engine light should come on. If it doesn’t, check the 50A fuse located near the battery. Check for signs of corrosion on the wire connector or fuse and check for open.

If the fuse and wiring test good, move on to check the power and ground connections at the ECM. If they check out, ground the check engine light wire at the ECM and make sure the check engine light illuminates on the dash. If the check engine light comes on when you ground the wire at the ECM, replace the ECM.

Check resistance on the digital bus

Next, use an ohmmeter and check resistance on the communication circuit at the diagnostic link connector (DLC) on pins 6 and 14. Resistance should read around 60Ω. If you get an ∞ or OL sign, there’s an open in the circuit. If you get a resistance reading around 120Ω the problem is in one of the modules on the communication bus.

Cobalt wiring diagram

Cobalt data bus wiring diagram

Disconnect the modules one at a time and jumper the connection to the bus. If that restores communication, replace the disconnected module. In this case, the modules are:

Remote Control Door Lock Receiver
Theft Deterrent Module
Inflatable Restraint Sensing and Diagnostic Module
Instrument Cluster
Digital Radio Receiver
Electronic Power Steering Control Module
Driver Information Dash Display
Vehicle Communication Interface
Electronic Brake Control Module

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Posted on by Rick Muscoplat

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