Phantom problems, like doors locking and unlocking on their own, in a vehicle can be tough to diagnose. SureTrack community member dicksrepair had a Chevrolet Silverado in the shop that would lose power and the door locks would act up after a cold start. They posed the question to the community, and with the help of fellow community member ericsautomotive and others, they were able to resolve the issue quickly.
The following Community Fix summarizes the interaction between members of the community that led to the solution.
2004 Chevrolet Silverado 2500 HD 6.0L
Throttle drops out, door locks cycle, added ground wire.
Customer complains that when vehicle is driven cold, door locks will lock and unlock and throttle is unresponsive.
Diagnostic Steps Performed/Parts Replaced
Performed a cold start drive and after one mile door locks will lock and unlock, dash lights all come on, throttle goes to idle. This will happen on and off for about three minutes. Sometimes it will go into reduced power, sometimes it doesn’t. Have checked all grounds and all ok. Checked all wires and found no breaks. Throttle body has been replaced, ECM was replaced as well as throttle control module. When it acts up you can see a 12 volt spike on the data link wires from throttle control to PCM. Removed all modules from class 2 data link and still acts up when cold. After it warms up it runs great but let it sit over night and it does it again. Any idea what is spiking my data link to throttle control module? All other modules are on another data line.
Best Answer from Community Member ericsautomotive
Double check the grounds at the right and left rear of the engine.
After re-checking all grounds I hooked up the lab scope up to the PCM, BCM, and throttle control module grounds at the modules. When the truck acted up I got a voltage spike on the PCM ground. Ground g103 was good so I added ground from body to PCM and that fixed the problem.
Added ground wire from body to PCM, vehicle no longer acts up.
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