H3 Electrical Issue
 

Last November I bought a low mileage (34,000) 2007 H3 Base. The paint was great, the interior looked brand new. I thought I had found a great used car for my boys to drive. Within a week I discovered the headlights would not turn on when the headlamp switch was turned to the on position. The Lexus dealer where I bought it sent it over to one of their sister dealerships (a GMC dealer) and they replaced the BCM. I thought everything was fixed. In the next month I started having issues with it starting. It would not turn over at all. I checked all the fuses and relays and could not find an issue with anything. I did a search of the internet and found post after post about the Passlock system malfunctioning with little or no answers as to WHY. I ended up purchasing a Passlock bypass module and installed it myself. Everything was fine for 3 months. I went to pick up pizza one evening after running some other errands. I left my son in the car and went in to pick up the food. I had to wait about 10 minutes. When I returned to the car I put it in gear and the wipers turned on and it died. The wipers kept going. I shut the car down, the wipers stopped. I restarted the car and turned on the wipers. The car died. I turned off the wipers and restarted the car. I put it in gear; the car died. i fiddled with it another 10-15 minutes until I finally gave up and had my wife come and get me. The following morning I went down and got in the car, It stated fine, I turned on the wipers, they worked as they should. I drove home and parked it.

I fix things for a living. I know the BCM and PCM are just specialized PLC's that have programs installed to run the car. Would a voltage drop to the module cause it to malfunction like that? Should i be looking at every connection in the wiring harness making sure they are clean and tight? Is there a tool out there that lets me monitor the BCM and see what signals it is getting in / sending out? I do have a scan tool but that only tells me trouble codes, not what the BCM is doing.

I have a complete wiring diagram for the car (all 122 pages) and I have 3 Fluke multi meters at my disposal.

I know, some of the veterans of this forum are going to ask/suggest, "Have you replaced the OEM battery connectors?"

BTW, "WOW!" on the low miles. I found my '07, last November also, And I thought I did good at 86K miles.

EJ

On top of battery terminals check all grounds. These are very sensitive to the grounds being intact.

Question.... does it have a sunroof? If so, has the passenger carpet been wet? If so again.... search: fix for sunroof drains ..... in the search box.

Yes, the POS OEM Battery Terminal Connectors are garbage, you may think they are tight, but that would be by divine intervention, as none actually are as soon as anybody disconnects the battery for any reason. That "anti-corrosion stuff" is not supposed to be on the terminals, only at the bottom under the connectors, it is not a proper conductor.

No sunroof. I have one of those on my H2 and it has been a headache for over 10 years. If we didn't have a garage to park it in we would be using the inside as an aquarium.

I will buy new battery cables and install them this weekend. I also plan on chasing down all the grounds and making sure they are properly connected. The wiring diagram I have tells me where all the termination points are; it is just getting to them.

The Terminal Connectors are a known issue, the cables usually are not. Lots of threads here on replacing the OEM Battery Terminal Connectors. Good luck. Let us know how it goes.

You need a dealer to use a GM Tech II computer to check the integrity of your connection between the BCM and ECM. There is a good chance your ECM and potentially your ignition are both bad. Also a good chance you might need another new BCM if it was damaged by your ECM in the recent wave of malfunctions. This exact behavior happened to me 2 years ago, and it could not be fixed until we did a clean 1:1 install of new ECM, BCM, and ignition, all programmed together. There is likely KAM (keep alive memory) in our BCMs, and people rarely use battery tenders with these trucks, so your low mileage means it probably sat with a dead battery more than once, and the KAM module in the BCM died, which stores everything required to operate everything except the core motor functions. I rarely drive (2010 with 61k), so we think sitting destroyed my BCM, and which in turn caused voltage drop issues, destroying the ECM.

Also be sure you are getting new BCMs that are fully functional. We found that most had dead or dying KAM modules from sitting in GM’s warehouse for too long.

That is the main difference; mine has behaved since it's incident. I have had zero issues since it freaked out; I just don't want cause another problem and possibly damage anything before I replace the battery cables and check the grounds. I'll look into the ignition circuit and see how that ties into everything.

Mine failed a couple times before it completely quit. Sometimes it would happen months apart. From start to finish it was about 9 months (first symptom to flatbed).

I highly recommend checking the connection. It won't damage anything by doing so, and you might save yourself a lot of $$$ in towing fees and emergency repairs, plus waiting time (any shop you take it to will need to order the parts from one of GM's warehouses, and they are extremely slow).