99 K1500 burban electrical issues

[99BoatHauler]

Hey everyone, 

 

New to the forum but I've browsed before when trying to figure out some of the issues I've been having with my 1999 Chevy Suburban 1500 5.7L 4WD. I bought the truck from my old neighbor because I needed something to tow my ski boat to the lake and back. I knew the truck was a little rough around the edges and needed some work but I was okay with that since I know how to work on cars and I only need to tow the boat about a mile round trip to/from the lake. The truck started and ran great after I bought it but it started having some odd issues.

 

1. There's no communication between the scan tool and DLC. There's good power and ground to the DLC, the cigarette lighter fuse is not blown. Not sure if this is related to the rest of the problems but I think it's possible.
2. The Check Engine Light does not illuminate when I cycle the key or turn on the vehicle. 
3. Intermittent battery drain.

 

Since the truck was still starting and running just fine, I figured I would leave it be and I'd get around to fixing it eventually. It developed a fuel leak from the lines near the tank about 7-8 months ago and I didn't want to deal with it during the winter so I let the truck sit until the weather got nice and I was able to replace the whole fuel system from the tank to the motor (not the injection system). Before I replace the fuel system, I drove it around the local industrial park to try to run some fuel out of it and the following issues started.

 

1. Truck stumbled, the Airbag light, Service 4WD light came on, but kept running. 
2. Now, the Airbag light, Service 4WD light come on every time I drive it (4WD seems to still work).
3. Power/Heated seats inop
4. Intermittent battery drain turned into a consistent battery drain. I put in a battery disconnect that I use every time I let the truck sit for more than a day.
5. Power Locks inop

 

I started to get pretty confused and started trying to find some kind of common ground or module that would explain all of these issues so I went ahead and did the fuel system work and it's back up and running again.

 

I drove it again after the fuel system repair and even more things either stopped working or started acting weird.

1. Radio and temperature/compass in the mirror work great at idle, but both turn off above 10-15MPH.
2. Turn signal on/off speed varies from fast to slow and interior lights dim/brighten opposite of the turn signal turning on/off
3. Wipers are slow/dont work at all
4. Cruise control inop
5. Dash/cluster lights inop
6. Power windows slow up/down

 

So tell me what you guys think. I'm thinking there has to be a bad ground somewhere. I'm going to go through the truck and replace/clean grounds from front to back and see what happens, although I know that G202 is behind the dash and may be a huge PITA to get to, is that accurate? Has anyone experienced something like this? Is there a module like the BCM that could be bad and bringing down the communication lines, causing the no DLC communication?

 

Thanks in advance!

Adam

Edited May 9, 2019 by 99BoatHauler

[wreckdiver230]

Adam , i watch south main auto on you tube , there are several others who do this type of diagnosis , but he says  when not sure where to start get a wire diagram and do the the easiest circuit that is  acting up, like a cigarette lighter or turn signal . and go from there

[TW97C1500]

I've read numerous "experts" posts and watched videos and it's a pretty common statement that when you get your type of cascading electrical gremlins the problem is usually grounds.  Being a Suburban, you have that "interior lighting module" (or whatever it's called) for the back seat & cargo area lights and that could be a culprit.  It, or the wires going to it.

[99BoatHauler]

@TW97C1500 I haven't heard the term "cascading" for electrical problems but that's exactly how I would describe it. I looked at the ground straps at the back of the engine and the straps themselves look a bit corroded but are still attached. I'm going to replace them and see what happens. Also, I haven't heard of this "interior lighting module" before. Could you explain how that could be the culprit? I'm not sure I see the relation other than the fact that they share a ground.