Electrical Gremlins
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CF Beginner
Joined: Apr 2020
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Electrical Gremlins
I have a 2005 Silverado. I just put a new engine in at 181000 miles. It ran great the first day. This morning I was headed to work and some gremlins came out. The doors started locking and unlocking, instrument cluster went bonkers and it gave a “service brake system” warning and derated itself. I pulled over and turned it off, waited a few minutes and then it was fine.
I left work headed to lunch and it did the same thing. It seems to only do it for the first few miles then there’s no issues.
anybody have an inkling what could be happening?
thanks in advance
I left work headed to lunch and it did the same thing. It seems to only do it for the first few miles then there’s no issues.
anybody have an inkling what could be happening?
thanks in advance
CF Veteran
Joined: May 2011
Posts: 1,578
Likes: 302
From: Central Iowa
x2 on checking grounds.
Symptoms like you describe are usually caused by intermittent connections or low supply voltage to the respective modules; however it could also be due to wiring harness damage or moisture intrusion into the harness or module. Start with the easy/obvious and go from there.
Other possibilities (in no particular order) -
1) Loose charging cable or plug on the alternator (Inspect terminals in plug to see if they’re spread out). If you’re not certain of the alternator’s condition, check voltage at the battery at idle with as many accessories as possible running (lights, radio, HVAC etc). Voltage should remain above 13.0 volts.
2) Loose cables on the battery, particularly if they’re side post (GM’s favoritest battery - I’ve seen them loosen up in as little as 10 miles). If the bolt threads are stripping, remove the insulator sleeve and replace the bolts with a 3/8x16x1.25” bolt and nut. Snug the bolt into the battery then use the nut to secure the cables tight against the terminals. Make sure to clean as needed and apply a protectant. As with the alternator, test battery if you’re unsure of it’s condition.
3) Make sure all fuses and relays are tightly seated into the fuse boxes, both under the hood and in the cabin.
4) Inspect the wiring harness for damage, particularly under the driver steering column area if any accessories have been spliced in (trailer brake controller, remote start, etc).
5) If using an accessory in the 12v socket, such as a phone charger, or in the OBD2 port, such as a monitor, unplug it. I know it sounds silly, but for at least the last 10-15 years, GM has issued service bulletins on almost every model regarding devices that plug into these ports causing trouble. The list of symptoms is vast and I question if all the symptoms they list are actually possible, but I’ve also run into it a few times, so it’s worth a try.
6) Have the module network scanned for codes - this will pull codes from the BCM, HVAC, instrument cluster, and other modules that just aren’t accessible using a basic code reader. If you don’t have access to one, make some calls to local shops - some may do it for free while others may charge a minimal fee. Expect a dealer to charge a diagnostic fee in the neighborhood of $100. Just be clear that you only want the codes read and that no further diagnosis is to take place (if you’re not gonna wait on it).
Symptoms like you describe are usually caused by intermittent connections or low supply voltage to the respective modules; however it could also be due to wiring harness damage or moisture intrusion into the harness or module. Start with the easy/obvious and go from there.
Other possibilities (in no particular order) -
1) Loose charging cable or plug on the alternator (Inspect terminals in plug to see if they’re spread out). If you’re not certain of the alternator’s condition, check voltage at the battery at idle with as many accessories as possible running (lights, radio, HVAC etc). Voltage should remain above 13.0 volts.
2) Loose cables on the battery, particularly if they’re side post (GM’s favoritest battery - I’ve seen them loosen up in as little as 10 miles). If the bolt threads are stripping, remove the insulator sleeve and replace the bolts with a 3/8x16x1.25” bolt and nut. Snug the bolt into the battery then use the nut to secure the cables tight against the terminals. Make sure to clean as needed and apply a protectant. As with the alternator, test battery if you’re unsure of it’s condition.
3) Make sure all fuses and relays are tightly seated into the fuse boxes, both under the hood and in the cabin.
4) Inspect the wiring harness for damage, particularly under the driver steering column area if any accessories have been spliced in (trailer brake controller, remote start, etc).
5) If using an accessory in the 12v socket, such as a phone charger, or in the OBD2 port, such as a monitor, unplug it. I know it sounds silly, but for at least the last 10-15 years, GM has issued service bulletins on almost every model regarding devices that plug into these ports causing trouble. The list of symptoms is vast and I question if all the symptoms they list are actually possible, but I’ve also run into it a few times, so it’s worth a try.
6) Have the module network scanned for codes - this will pull codes from the BCM, HVAC, instrument cluster, and other modules that just aren’t accessible using a basic code reader. If you don’t have access to one, make some calls to local shops - some may do it for free while others may charge a minimal fee. Expect a dealer to charge a diagnostic fee in the neighborhood of $100. Just be clear that you only want the codes read and that no further diagnosis is to take place (if you’re not gonna wait on it).
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