If you replace a main battery in a dual battery G.M. start/stop system, take care. Both batteries are AGM and the main battery is very large for the size of the vehicle. We had a vehicle come in that needed a main battery, which is an expensive item. He declined the repair and took the vehicle. Two days later, it was towed back in as a no start.

Looking at the vehicle, he had a battery installed by a parts store. It was a conventional battery much smaller than the original. The dual battery control module had a catastrophic melt down. The plastic cover melted and ran all over the new battery. On closer examination, we found the electrical connector to the DBCM not fully seated and clipped into place.

Although documentation is not easily found, if the DBCM connector is unplugged for a period of time WITH the battery cables connected, the DBCM will overheat. In this case it was driven with the connector unseated, causing a major overheat and melt down. The battery can be easily be replaced without unplugging the DBCM by pivoting the plate upward and sliding the battery out toward the front of the car.

As always, with new technology, the easiest job is not always simple any more and the correct procedure should be investigated BEFORE performing repairs.

It's funny that the same day, I saw a dual mode hybrid Silverado that had a 12 volt battery replaced by an aftermarket shop. Afterward, the SES and service hybrid system message came on and would not clear. Of course, they said that the battery replacement could not have affected it and it needed to go to the dealer.

Looking at the vehicle, it had BECM and battery SOC codes set. The hybrid battery showed 280 volts and a SOC of 42%. If the 12 volt battery fails and is not replaced soon enough, the hybrid battery can become depleted as in this case. The fix was easy. Just perform the running battery charge procedure to raise the SOC over 70% then reset the SOC by 12v interruption to reset the SOC to a nominal 60% and retest. The SOC now showed 72% and the hybrid battery voltage was 328 volts. The codes set and stayed off.

Again, make sure that you know exactly what you are doing or send it to someone trained and tooled in the system

James Avery
Technician/Technical Information Specialist
Stingray Chevrolet
Plant City, Florida, USA