2002 Silverado Electrical Problems

sodell · September 16, 2011

I have a 2002 Silverado regular cab with a 5.3L, auto, 4X4. Everything was fine on the truck and then I parked it for a couple of months. When I went to start the truck I noticed that the battery was dead. I then tried to jump start it. I got it started but noticed that the alternator was not charging the battery. At the same time I kept hearing a popping sound coming from the radio and I had 3 lights in the message center. (battery, security, and ABS). I bought a rebuilt alternator and installed it. This fixed the charging issue. I also removed the radio and put my original factory radio back in. (The radio that was making the popping noise was a factory one but I got it from a junk yard because it had a CD player. It worked fine in the truck for over a year before this happened.) With the original radio and rebuilt alternator, I still have the security light, battery light, and abs light. I found that the light in the message center never turns off and it drains my battery so I have been pulling the radio fuse when I park so I don't drain the battery. Also after ~30min the BCM is still drawing a current with the key off. AlsoI tried connecting an OTC scan tool but could not communicate with anything. I checked the power and grounds at the DLC and the BCM and they are all working. I even pulled the splice out and tried communicating with on the BCM with a jumper wire between the DLC and the BCM with still no communication. I believe I know why the battery light is on but I'm not sure if that is causing everything else. With the rebuilt alternator, I am getting positive voltage at pins 1 and 2 of the 4 pin plug, however my truck has wires on pins 2 and 3. I am taking the truck back to the alternator rebuild shop to get it fixed but I don't think that is the only thing wrong. If anyone has any ideas where to look to next, the help would be much appreciated.

Shawn

sodell · September 17, 2011

After taking the alternator back and getting a different one. I am seeing a voltage on pins A, and C of the alternator while the engine is running. There is nothing on the wiring harness side of pin A. Pin C is the duty cycle signal and pin B is the voltage signal. I am getting 0V out of pin B. Is this supposed to be 0, +5V, or +12V while the alternator is running?

Thanks

Shawn

govtech · September 17, 2011

what voltage is at the battery while running ???

sodell · September 18, 2011

The alternator is charging. The system runs at around 15V.

sodell · September 24, 2011

I used a scan tool to pull module by module and found that I can communicate with the BCM with the connectors pulled from the ECM. However, if I pull the BCM, I cannot communicate with the ECM. With both connected I cannot communicate with either one.