Blufie

PROBLEM SOLVED (I love to be wrong). Finally got some warmer weather and started from scratch and basic looking for this issue in the wiring. I found two issues, the first was one of the coil pack wires on the donor motor had bare insulation and was grounding out, the second was the primary ground wire by the cam position sensor had broken off. I had even soldered a new ring terminal to it but somehow it got tugged loose. This is very hard to get to on my truck (behind the manifold and deep) but I built an entirely new segment with a heavy steel terminal, and soldered that on it. When I corrected these two issues, the starter fired on first try (with the original BCM). Got it running and its motoring along fine now. It is amazing that a bad ground wire can cause so many issues that seem unrelated but it did. I didn't get many replies here from GM techs, which I understand and that is fine. I too have spent hours and hours answering questions on other forums and it doesn't pay bills, satisfy my family, or teach me much, but I try to give back. I do however hate it when people post a question, get a few replies, and the thread goes unresolved because the OP never updates the final outcome (good or bad). Hopefully this will help someone else, and thanks to the people that read and the ones that replied.

So, got the used bcm in and with it plugged in and the key turned to aux then off appeared normal. I could hear the throttle body advance as expected when I turned to ignition position but then I immed heard a fluttery clicking noise from the top front of the engine (very fast paced clicking kind of like a starter solenoid with too little current), so I turned key off and it continued until I pulled the battery. I tried to cyle to on again, determined to locate the clicking, and the truck was back to behaving like it did with the original bcm, no response and light staying on. I think bcm number two just went bye bye. So, I need to figure out how in the world I created some electrical gremlin. I would like to try and manually activate the power to the engine PCM and circuits that the bcm powers to diagnose the source of the noise and then trace that circuit. What a pia.

Thank you for replies! I tried the relearn procedure several times but the security light never goes off (or blinks). I never unplugged anything at ECM or PCM, just the wires running to the engine of course. I can't remember unhooking any grounds except the three I mentioned but it seemed like a ground issue initially. I just hope that my fiddling with it didn't burn up the BCM. But, I have found 3 other examples posted of similar condition and two had bad BCM's suddenly fail. Interestingly, two of these people had issues after the battery discharged and they tried to start the truck. I need to get a wiring schematic and start checking for any missing grounds. Anyone know how many grounds and where they are for this truck ;-)? Also, best manual to start the trouble shooting? Would a Haynes or Chilton's work or do I need the GM factory? Happy to entertain more suggestion or diag steps.

Hello all, I had to swap the engine in my 04 Silverado (4WD crew cab z71 - if it matters) with salvage unit. Took replacement engine down to long block and used everything from my original engine except cam/crank sensors from old engine (donor engine was out of 04 suburban). After connecting it all back up, no crank issue appeared. I know that anything is possible with wiring breaks, but I was careful to repair and reattach any grounds, and most of the electrical is plug-n-play so hard to mess up. Anyway, here are the symptoms... Key on, dash lights and radio come on as normal, security indicator light turns off. Won't crank when key moved to start. After about 30 seconds, the security light comes on solid, and the radio, security light, and daytime running lamps stay on for about 10 minutes after the key is removed (door open/closed make no difference). I cannot communicate with the onboard computers with my OBD adapter (using Torque - just to read codes and verify sensor output). There is power at the OBD port, but software cannot find the ECU (or whatever this talks to). Key fob no longer activates the power locks. The only thing that was abnormal about the first power cycle was some unusual clicking near one of the fuel injectors for cylinder 1 and the battery was only outputting about 10 volts. I charged the battery and I cannot find any obvious shorts or missed connections or wires but still stuck. Diags: Checked all the fuses in the boxes under hood and in cab (have not checked the mega-fuse yet but have lights and power so could it be bad)? Verified there are no unhooked grounds from original harness. I have one wire from harness on back of block by cps, one ground strap on head to the firewall, and another wire from wiring harness hooked to same location as the negative battery cable. If I jump the solenoid at the starter, the engine will crank but not start. I suspect that the BCM is toast but would love to try some more trouble shooting steps or get some expert advice. I would also appreciate a suggestion on the best service manual to purchase for this vehicle. thank you all for the time to read all this! Steve