Usually I post more complex repair procedures. Lately, I've been trying to submit less complex problems for those of us just getting used to data communications problems. This is an example of such.

A 2011 Corvette came in yesterday with the complaint that the key fob was damaged by closing it in the door and wouldn't work at times. The customer had only 1 fob and wanted it replaced with a new one. I pulled a new fob from parts and tried to program it to replace the #1 fob that was damaged. If you don't program a new fob on a Vette to replace either the existing #1 or #2 fob, it will program into position #3. It will still function normally but personalization functions will not be enabled.

The new fob would not program as the RCDLR would not respond. Doing a fast scan check, I saw all the class 2 modules were unable to communicate although all the GMLAN modules communicated normally. The high speed modules all had multiple U codes set as current and history.

My first diagnostic step was to check the Class 2 bus resistance...

2011 Chevrolet Corvette, ECM/Inputs/Outputs Photo

I don't see a problem inhibiting communication there...How about the bus voltage?

2011 Chevrolet Corvette, ECM/Inputs/Outputs Photo

OK. Here's our problem...excessive voltage on the bus, but from where? Usually this is caused by a module leaking voltage onto the bus, but which one? I saw a clue staring me in the face...

2011 Chevrolet Corvette, Photo

An aftermarket Pioneer Nav radio has been installed. We have many problems with aftermarket components either causing communication problems or key off draws. Since the JX 208 bus connector is easily accessible under the R.F. access panel, I pulled the comb, opening 1/2 the bus that the radio was on. That restored communications with all the Class 2 modules on the JX205 bus connector. Assuming a radio fault, I backed out terminal C, leading to the radio, from the JX208 connector and reinstalled the comb. Let's look at the voltage now...

2011 Chevrolet Corvette, ECM/Inputs/Outputs Photo

That's more like it. All communications are restored except for the radio and I was able to program the new key fob without a problem.

James from Florida

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