Thread: Help diagnose: courtesy lights always on *SOLVED*

I read your post and subbed right away. Hoping you find a fix to help guide me. Have you checked everything I have checked?

ive found 2 broken wires before at the door to unibody boot.

gm went to smaller dia wires as they tended to work harden and break less than the thicker wires back in the day...but it still happens.

diagrams are hinky, look at your build date, this will give you an idea if you need to lookup the diagrams for the prev or next model year to find the right colors... if made in 3/4/5/6 month of 97, lookup a 96 diagram, if made at 5/6/7/8/9 of 97, look at 98.

unless the break is obvious its not worth repairing, far easier and reliable to run a new wire

I could see how this would be a common problem. Those wires aren't real beefy. I visually inspected, ohm'd, and disconnected the door wires to rule out the actuator/switch. Still, no one has said definitively, if the dic will or will not show a door open if the actuator is bad. My dic shows all doors shut when the lights stay on.

one thing i can tell you is that ive been finding lots of odd ground loop issues with the modern cars. even just a tenth of a volt voltage drop is enough to cause some odd ****.

id suggest hooking up a red brick/commercial scanner to the BCM and see if its reading the door switches properly. you could also try running a direct jumper from the latch/sensor assembly to the bcm for a temporary test. its entirely possible that the vehicle had an alarm at one time and some will tap into a door sensor to kill the signal and light up the interior according to the alarm...those setups have gone by the wayside over systems that comm with the BCM via the databuss instead of altering circuits.

its possible this car had an alarm configured as such...

This last post got me thinking... At some point, something was installed that tapped into the three wires at the BCM that control the door actuators. I wasn't real confident in the remaining connection so I repaired them. Also, There is (was) a security device installed. Peeled that out too.



Took a good look at all the wires while I was in there. Everything looked good, I suppose.

I've heard stories of how touchy the electronics on more modern cars can be. I'm hoping my ride is old enough that it's a little more tolerant. I mean, it's old enought that the BCM is plug and play. I doesn't need to be programmed. Just as a reference.

I could back probe any of the connections at the BCM, but honestly, I'm not even sure what I'd be looking for...

I disconnected the battery when I put the vc gaskets in. Sat disconnected for four or five days. When I reconnected the battery and ran it to bleed the cooling system, the lights worked as the should. For about 10 minutes... As it was sitting there running (to reach temp) with all doors closed, all the lights came on without any input. Just sitting there idling, and "bing", the lights pop on. So confused....

Update: I disconnected the battery again to do a parasitic draw test. (Mostly cause I just watched a YouTube video, and wanted to try it for myself). Came up with 41 milli amps. I'd say that's okay. Anyhow, I figured, what the heck. Last time I disconnected the battery, the lights started working again. So, I threw a fuse in and gave her a go. Starting at the door closest to where I was (right front). I popped it open then quickly shut it; Lights theater dimmed like they should. Yay! On to the right rear. I popped it open then quickly shut it; Lights stayed on. WTH!? I disconnected the harness for that door at the jamb. Walked around the car, trying all the other doors and the slider on the headlight switch. Everything worked like it's supposed to. Hmmm. Maybe on to something here. Will play with it some more tomorrow to confirm. It's late.

Now suspect the RR door actuator. Really!? The right rear? That's like the least used door!

Well, never mind... Problem came back after the car sat for an hour. Seems odd that disconnecting the battery resets the problem. Can't be a door actuator. Not knowing the full history on this car, but only knowing what I've seen, I'm thinking there's a broken/exposed wire shorting to ground somewhere.

I got a couple trouble trees from some one at a dealership that I'm going to work through.

604292 - Diagnostic System Check - Body Control System
600270 - Courtesy Lamps Always On
600274 - Courtesy Lamps Inoperative

I'm sure I'll have more questions as I work through them.

The tree took me to the "Body Control System check." Ran the BCM system check, and there was a code stored.

chime.chime-pause-chime.chime-pause-chime.chime

I take that to mean code "2." Google tells me that this is "Power output circuit to courtesy lamps shorted to B+ or ground." Which makes total sense.
→ If yes, Refer to Body Control System Circuit Description for more information regarding DTCs. (Which I don't currently have.) Waiting to hear back from my source.

Not fixed yet, but moving forward. At least I'm not just blindly stabbing in the dark. Haha!

I disconnected the harness at the junction box under the glove box. Based on how it acted, I suspect the problem is after that junction.

Does anyone know where the highlighted diode in this diagram is physically located on a GP? I ask because the trunk light for this thing has always been screwy.



Or where to look for the most likely spot for a ground fault?

I'm seeing 0.3V on the negative side of my lamp sockets. Which, coincidentally, is the same voltage the GRY/BLK "Courtesy Light Control Output" wire is pushing (after theater dim). It starts at about 50Mv then ramps up to 0.3V after 25 seconds. So I know the BCM is telling the lights to dim, but something isn't listening.

Time to start chasing wires... On the bright side, I have an excuse to get my fuel pump rewire. I'd be foolish not to install that if I'm going to start pulling the interior apart anyway!

Question is, do I go ZZP rewire, or spend a little more for the racetronix one. I already have the racetronix fuel pump.

Racetronics/PRJ is way to go. My $.02 : )

Just seeing this again. Do you still suspect the diode? if so.. it's between two splices and I have the GM manuals. Those splices should be identified as to where they are located down to a few mm's

Honestly Bill, I'm not sure what to suspect. I just figured I'd check it first. The only thing that makes me think it could be that and not a straight up "short to ground" is the fact that the problem temporarily resets when I disconnect/reconnect the battery. That, and when I open the trunk, the trunk light does not come on until/unless I do something to command the courtesy lights to come on. (Open a door, lock/unlock a door...) Something is whack with the trunk light circuit also. Electrical is definitely my Achilles heel.

I think I just need to start inspecting wire.

Typically this is either the driver door switch for courtesy lights.. or a wire in the boot going to the door that has gotten broken. Those would be the first two things I'd be checking. And you could unplug door by door as you went to try and confirm it. Say you unplug all yoru doors and it still happens.. then you can move on to other stuff.

I also wouldn't say the BCM might not be bad and causing it.

Ya. Unplugged each door individually and checked. Also visually inspected the wires in the boot.

Tried a different BCM and it does the same thing. I think(?) the BCM is okay because I can see the theater dim happening on my DVOM at the GRY/BLK "Courtesy Light Control Output" wire.

Time to start ripping this pig apart. It'll give me a chance to super clean it, and properly install the FP rewire, I suppose.

The thing that screws with me is.. it's intermittent

Predictably intermittent...

Battery disconnect makes it work right for a while, then problem reappears. Like I said, electrical is NOT my bag, but that's kind of why I was thinking it was something physical like a relay or diode. When the circuit goes cold it resets. Then once it heats up, bing, she's locked on.

Maybe, just for grins, I will disconnect/reconnect the battery and check the readings for the GRY/BLK "Courtesy Light Control Output" wire.

Hmmm I'd bet that once it sees the short, they stay on. But unplugging resets the code.

I don't doubt that.

Would you agree that my next step is to tear in and inspect the wires? If that's something I have to do, that's fine. I'm willing to do (almost) anything to get the light's working proper again.