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[Shorty Cox]

I need help. Put your thinking caps on. (2012 Chevy Suburban LTZ) Yesterday morning (10-8-18) the wife and I were traveling in a heavy rain. I flipped the dimmer switch from bright to dim, all dash lights, radio, etc. when off then immediately every dash light came back on to include every “caution” light, all four door locks activated, and the transmission down shifted several gears. Just as quick, everything flashed off again then back to normal. This happened three times in approximately 15 minutes each time I flipped the switch, then has not happen again. Thoughts?

[Steeveedee]

Originally Posted by Shorty Cox

I need help. Put your thinking caps on. (2012 Chevy Suburban LTZ) Yesterday morning (10-8-18) the wife and I were traveling in a heavy rain. I flipped the dimmer switch from bright to dim, all dash lights, radio, etc. when off then immediately every dash light came back on to include every “caution” light, all four door locks activated, and the transmission down shifted several gears. Just as quick, everything flashed off again then back to normal. This happened three times in approximately 15 minutes each time I flipped the switch, then has not happen again. Thoughts?

That stuff starts acting like some UFO blinky lights, I sell it. Maybe not the answer you wanted.

['63GENIII]

Sorry for the long post. You may want to skip to the end.

2004 Yukon Denali here. For several years I chased intermittent issues similar to the ones you described. Wipers, door locks, interior lights, the UFO is landing in your instrument cluster thing, climate controls (full hot on a 108 deg day). All except the transmission downshift thing. Then it could be normal for a few weeks to a month or more. Frustrating as HE double hockey sticks!

Reprogrammed the Body Control Module, bought a new one and had it programmed too, had the dash completely apart looking at the VATS sensor thing in the ignition switch and I'm sure a few more things that Ive forgotten. Had it a the dealer twice to the tune of 2k for them to say it was the BCM once and the second time they couldn't replicate the issue. It died on the way home that day and I was broke.

The car would go through batteries faster than my kid's X Box remote controller on a new game release day. Not the cheap batteries from Autozone either. Optima Red, Yellow, Blue. Megatron and Megatron Plus. All eaten up without mercy. Every 1 - 1-1/2 years it was a $200+ battery. It would run fine for a while but I knew it would be short lived before the electrical shenanigans started again.

In December of '15, the beast went down again. This time, not charging the battery and battery discharging 22mA if I remember right. I read up on the charging strategies (controlled by the BCM IIRC) programmed into the vehicle, normal discharge rates while the car was "sleeping", tested for the constant drain that always seemed to be present, pulled the dash apart again to test and re test every single damn relay and fuse that I could find and gave up right around Christmas that year.

At the same time and unrelated, I was working on putting the 7.4 Vortec and its black box PCM into the '63 K10 and had read that a lot of guys were swapping to the 0411 PCM for easier programming. Well, I knew there was one of those in that Denali in the driveway so I wanted to take a look at it to see if there was any compatibility in the connectors of the two PCMs. So I pulled the PCM out of the Denali which is located just below and away from the battery on the drivers side under the hood.

Upon pulling it out, I looked at the pins and noticed that a couple of the brass pins were corroded and green. Weird I thought seeing as I had never heard of any issues with the GM weather pack connectors.

I also looked at the connector's female pins and they were black (corroded also).
Not being one to leave it the way it was, I disconnected the battery, did my best to discharge all electricity that may have been present in the system and started cleaning the corroded pins with a jeweler's screwdriver and some super fine emory cloth. The female pins got a light brush with a super small welding tip cleaner.

Before I put it all back together, every female socket got a squeeze of Perkins Dielectric grease and the outsides of the connectors were sprayed with silicone spray to try and keep any possible moisture out.

After it was all together, I was looking through the drivers wheel well and did notice a clear shot from the wheel well, under the inner fender right to the back side of the PCM connectors where (I thought) water could be sprayed with sufficient force from running through a puddle, maybe getting into the connector somehow.

My wife NEVER slows down for puddles unless there is a boat sitting in it. Ive gotten tired of telling her. She'll never get it. This was a plausible explanation to me at the time.

Long story longer, since January of '16, we've had not one issue (knock on wood) to speak of. All due to a chance look at the PCM connectors for a completely different reason. Almost 3 years and 36k miles.

These cars do some funny things when the battery voltage is just slightly low. I think that the BCM is very sensitive to erratic voltage / charging.

Could be coincidence. Could be luck. Either way, next time it starts acting up, I gonna take a quick look at those connectors first.

Hope you find your "gremlin" easier and quicker than I did. Pretty sure that shaved a few years off of my expected life span and definitely gave me some gray hair.