2002 GMC Envoy Intermittent Dead Battery
A 2002 GMC Envoy came in from another shop with a complaint of an intermittent dead battery. The other shop informed us that the Envoy was in their shop for same problem a few times in the past month. We were informed that they tried to get to the root cause of the problem without any success. Since they had the Envoy so many times the vehicle owner was now pressuring them, so they decided to bring the Envoy to the closest GMC dealer and get it diagnosed. The dealership told the shop they uncovered the parasitic draw and repaired the problem. A few days later the shop received a call from the Envoy owner who stated that the battery was dead again. Now the shop was at their wits end, so they called us and asked if we could check it out.
My lead tech Bill checked the problem out by installing the Fluke i30s (Figure 1) low current probe and connected it to a Fluke meter. The meter was reading 199.8 mV that converts to 1 amp nine hundred and ninety eight milliamps. The conversion rate is every 100 millivolts equals 1 amp.
Next Bill connected the Tech 2 scan tool (Figure 2) after removing the B+ Pin 16 wire from the DLC connector. The reason for PIN 16 removal was to make sure that the scan tool could not draw current from the vehicle.
The results of the module scan came up with the LGM (Lift Gate Module) and the ATC (Active Transfer Case) modules (Figure 3) that both displayed high activity. The ATC module also came up active, so we checked and found that the 4HI /4LO button was in the on position. Once we depressed the button the module no longer was active or counted up any longer.
The only thing left that could cause the draw was the LGM module, so we proceeded to the rear of the vehicle (Figure 4) and popped the rear lift gate cover where we found water.
Upon inspection, it was clear that this module had had sort of service focused on in in the past due to the evidence shown in Figure 5. We asked the shop who sent us the vehicle if they had performed the repair, but they replied that they had not. They thought that it was possible that the dealership performed the repair but could not confirm.
We proceeded with our diagnosis and disconnected the LGM module (Figure 6) and verified that activity stopped counting up and that the parasitic load dropped to approximately 32ma. Next, we backed the GMC out of the shop and parked outside, leaving it for the weekend. When we returned on Monday, we rechecked the vehicle and found that the intermittent current draw was no longer an issue. We called the shop and advised them that the module required replacement in order to solve the parasitic load and to verify that water intrusion possibilities were eliminated as well.
Here is a short video we shot detailing the vehicle issue.
Very nice write-up. I like the way that your team analyzed the CAN bus to isolate the problem. Fantastic!
Mike thanks for your comment and for reading the case study.
Hi Jerry. Nicely documented and a good approach on that old Class 2 beast.
I was still working part-time at a GM dealership in those days and lift gate modules were "frequent flyers", as the cause of parasitic drains on that platform.
FWIW, the HVAC control module on the early Envoys/Trailblazer could stay awake for as long as 4 hours, so it was always necessary to let the vehicle sit through a cold soak to be sure that everything went to sleep and stayed asleep as your tech did.
Martin thanks for your comments ...you are correct about making sure that the modules go to sleep. We have seen similar problems in the past. My tech Bill has a good memory and a good sense on how to diagnose problems. Bill has been with me for over 5 years and has gone through all my training classes. When we work together in the shop he is like a sponge that can absorb what I show him. We need more techs in the industry that are Bill's. Thanks again
Thanks Jerry. Although using factory tools in relatively unheard of out here in Maui, I did get my own Tech2 recently and learned a lot of neat stuff, like the Class 2 Message Monitor, by reviewing old GM TechLink articles found here;