GM Repair Questions? Ask a Mechanic for Answers ASAP
Hello and good morning. Here are your diagrams.
Your JA Expert,
I feel confident enough, in that if your vehicle came into my shop, I would start with these diagrams. I recommend you begin with these 3 diagrams and come back to me if you find any conflicts. If you do, I will dig for additional info for you. Start with these and see if the colors pan out. They should. If you find some additional control wires or conflicts when you get to the interior lamp control module, I will pull up some body control diagrams, but let's go there only if warranted. Start your diagnostics with these and post back to me your findings and if you need more info. I'll be available to you if that comes to be the case.
You will find it under the left side of the dash. Below is a picture and I am providing the 2 diagrams for the keyless entry system too.
Take a look a these pictures and let me know what you think when you compare them to yours.
Manufacturer supplied 2 different possible locations.Look for 5 wire connector with wire colors: gray, white, orange, pink & black.#PIT3819: Location of Interior Lamp Control Module - keywords control dim dome electrical entry ground illumination inoperative keyless lens light remort resistor RKE short - (Dec 23, 2005) Subject: Location of Interior Lamp Control Module.Models: 1995-2000 Chevrolet C/K Trucks, Suburban and Tahoe 1995-2000 GMC Yukon and C/K Trucks Classic Body Style Only The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this P1.Condition/Concern When diagnosing a dome lamp concern on one of the vehicles listed above, you may be unable to locate theInterior Lamp Control Module that is called out in the Service Manual.Recommendation/lnstructions :Only vehicles without Remote Keyless Entry (RPO AUO) will be equipped with a Interior Lamp Control Module. If the vehicle is equipped with (RKE) Remote Keyless Entry, the illumination module is a internal part of RKE Module.Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.
Take a look at this trouble chart and let me know where it leads you.
I have a good idea on how to narrow this down. You have a RPO list sticker in the truck, usually in the glove box. This is a sticker that has all the 3 digit option codes for the entire truck. Take a digital picture of it and upload it. I'll decipher the options and see what system is supposed to be in it. The sticker resembles this
I hope it came out ok and I realy appreciate the help. I'm sure if I can get to the right module controlling the dome lights, I'll be able to go further with the troubleshooting and order a replacement.
Ivan, I believe I found it. I did find the primary door lock control module in the area from the illustration. It was up a bit higher. I disconnected it and when I hit the door lock button, I still heard a relay clicking. I stuffed my hand way up in above the steering column and felt another module. I felt a relay click coming from inside of it as well when I triggered the lock button. You can barely see the plug end from below but I got a mirror stuffed in and the plug looks like it's the one in the images and so does the size of the module. It's going to take me a good while this evening to get that out of there and down to where I can address the connector and disconnect it to further troubleshoot. You don't need to dig into those codes further for now. I will let you know how it goes in a couple hours. Charlie
Thanks Ivan, for darned sure it'snot going to be real easy to get that module out. Looks like I will need to remove 2, 5/8" bolts and a 9/32" hex screw to loosen the plate that it's mounted to first and then go from there. That's why I elected to take a break for a bit. I am certain that clipping wire 156 will shut the lights off but I need to look a bit closer to decide whether that means the module is actually back because it looks like there are other connections to that module that could hold a fault too. I did electronics troubleshooting in servicing everything from CB's to Televisions for over 30 years and am still also a master electrician but mostly retired. Being analytical to that extent can sometimes be a curse ! I am no newcomer relative to zeroing in on the "what if's" then the "go to's". Overall that dome / coutesy circuit is a cake walk but when you throw in a module or 2, anything goes. Later !
Once you understand electricity, you can figure out anything. Let me know if you need anything, I'm here for you,
I'm supplying you the description and operation of the dome light circuit. I figure this will help you interpret what you have to this point, I'll put my thoughts at the end of this.
Voltage is supplied at all times from the CTSY Fuse 3 to the Courtesy Lamps, Dome Lamps and I/P Compartment Box Lamp. The Courtesy and Dome Lamps turn on when a ground path is provided by the Headlamp and Panel Dimmer Switch or one of the Door Jamb Switches.The I/P Compartment Box and Vanity Lamps have their own Switches that provide ground paths when their Switches close.UNDERHOOD REEL LAMP Voltage is supplied at all times to the Underhood Reel Lamp from the Horn Minifuse. When the Switch is closed a ground path is provided.COMPONENT ILLUMINATION LAMPS When the Headlamp and Panel Dimmer Switch is turned to the PARK or HEAD position, voltage is applied through the PARK LPS FUSE 9 and the closed contacts of the Headlamp and Panel Dimmer Switch to the Component Illumination Lamps. Since all of the Component Illumination Lamps are grounded G200, they light.ILLUMINATED ENTRY When a door is opened, the Illuminated Entry System is activated. After the last door is closed, the Dome Lamps will remain illuminated for 20 seconds or until the Ignition Switch is turned on which cancels this function. Voltage is supplied to the Module at all times through CTSY Fuse 3. The ground path is provided by CKT 150 to Ground G200. The Module senses a ground signal from CKT 157 when a door is opened. The Module then provides a ground path to CKT 156 which allows the Lamps to illuminate.
Did you do that last step of that trouble chart, where it wants you to test cavity B of the lighting control module to ground with a volt meter. It says if you have a volt reading of less than 10 volts, the module is to blame. Cavity B is the gray wire. I know the diagram shows that gray wire going to the remote lock receiver, but see if you have a gray wire on yours. On all of the diagrams, the lighting control module is a magic white box, no details are given. Let me know if your module shows a gray wire on that terminal. It wants this test with the dome switches disconnected. What I recommend too, is if you have that remote lock receiver, take your reading, then disconnect it and see if the lights go out, with the door switches disconnected. Including the rear door switches. Check your voltage on that gray wire. If you disconnect that remote lock receiver and the lights go out, I feel that is the module to blame. On that module power comes in from the headlight on the gray wire and goes out on the white to the lights. See what you find there. Ok, i just read your updated info. Under the floor is the most common point for issues. Wetness is usually the reason. I'll be right back with locations for those points. Here is some info. Let me know if you need more. There are 3 pictures for C301, so take a look on yours.
I/P Harness, approx. 12 cm into Crossbody Harness Breakout, toward C298
S246: Crossbody Harness, approx. 41.5 cm from LH Door Harness Breakout, toward C301
S417: Front to rear Body Harness, approx. 230 cm into Crossbody
Ivan, here's what I did tonight since I found the short to ground on 156. While that still doesn't rule out module problems, that short can not be there no matter what. I took down both dome clusters from the ceiling to be sure no screws were through the wires. They are both ok for that. I also pulled both sun visors to inspect for the same. While doing this, I kept the dome light fuse in place in the event an intermittant would show up during the disturbances. Last, I pulled the side panel at the driver's side area where the hood release is to expose all of the connectors in that body well. I disconnected one at a time and the short remained and ... the dome lights stayed on except in the case of the white connector. Unplugging that shut the lights down totally. I ran out of time to put the headlight cluster switch back into place (since it has the dome override in it) to see what happens then with that white connector unplugged. Here's where I am at right now Ivan, I want to rule out a ground fault in each door (not dome light switch wiring. That's all ok) but because all 4 doors also have the side lights in them with a 156 line. After that, it can be under the dash or anywhere that 156 is routed. I'm going to print out those locations in the morning as well and see what that yields. I really appreciate all the details and we're going to solve this soon.
Ivan, I am about to go back at it. Note, this vehicle is pristine. Can't find a spec of rust anywhere. TThe steel under some of the carpet I lifted when I bought the vehicle is showroom so even though I am not ruling out the fault being under the carpet somewhere, I doubt it will be because of moisture. Since there are no wiring faults of any other nature, I think that the cause of this fault is because of something having been taken apart and then during reassembly, a screw went through a wire. I would generally more so considerwire rotting from moisture in the case where there is an "open" circuit.
Now, relative to the carpeting and dome light wiring underneath it..... would that wiring be under the floor board panels at each of the doors or does some run up the middle as well? I'll check back in a bit. Heading out to work with C301.
More hints.... I disconnected C301 which does shut the lights off. After plugging in the headlamp switch assembly, I was able to use the courtesy switch to turn the door lights on but that did not turn on the dome lights on so there's a chance that C301 does interupt the fault but.... with C301 disconnected, I still read a short to ground on the white wire (156) at both the make and female sides.
Now, I went to the passenger side and pulled the lower kick cover. I disconnected all 3 connectors there and the lights still stayed on. Does that rule out the ground fault being on the passenger side ?
Last question for now .... Do you have access to any other kind of map that would more clearlty show all of the routing of wire 156 ? I know it is present in each of the 4 doors because of the marker lights. I also know it's under the dash and .... overhead to run the 2 sets of dome lights but just not sure how 156 gets there. I'm going back at it for a while. PS... In my earlier exploring, there's not a spec of corrosion at any connectors and as much of any harnessed that I exposed, the wiring is super clean.
I would agree, that the issue is upstream from that passenger side. I don't have a harness routing picture. I do have a factory wiring diagram, which may be what you are looking at as well. With the connector references, I can get illustrations and locations that can help form the picture of the routing. I do believe, if you have the bulbs in place, you may still show a ground as well. To truly test for continuity to ground, every item needs to be disconnected from the circuit and the fuse removed so the circuit is unpowered. Then you can go section by section, checking for continuity to ground.
Good morning, I think my next step is going to be to actually cut the white wire at C301 so that way the other conductors at that connector will remain in place. As far as pulling out all the bulbs go, according to the diagrams I have... pulling the fuse lifts that side of the circuit from everything. I'm using both an analog meter and... a digital to make certain I see 0 ohms to ground on 156 confirming a total short. I wish that the junctions for 156 were easier to locate and access because that would make it easier to separate them and narrow things down tighter.
Do you know if there are more factory connectors in the door posts between the front and rear doors? That might get me closer to ruling out a problem in the doors themselves. I am headed in that direction because of the likelyhood that something in a door may have needed to be repaired at some point in time and 156 is definitely in each door. Also, to learn where the wiring is routed to get to the dome lights will be helpful. Actually, any hints you can find about the 156 wiring will be helpful. Just finding and cutting every white wire may be the wrong approach until I exhaust other search means first.
I won't be back at this until later today so feel free to share more. Thanks again, Charlie
See if you can match up the splice locations that I gave earlier. I would definitely work systematically to eliminate big sections of 156 as you can. I think the splices are under the carpet, see if you can verify where the harnesses cross the body.
The only other connectors are C298 and C302. C302 is next to C301. C298 is in the dash as indicated below,
Here are my diagrams
Ivan, new details. I think C301 is the key point from here. Tonight, I plugged the receiver module back in and also reconnected the headlight switch. With C301 disconnected, the system and door lights and under dash lights all work properly even with the delay feature going. The 2 dome lights do not work at all. There are actually 2 white wires in the C301 connection. My guess now is that the fault is somewhere between C301 and, the ceiling dome lights. Every thing else is pretty much ruled out. Last step I did for the evening, I cut one of those white wires and plugged C301 back in. The dome lights then came on but, they do not go off with the rest of them when the module times out. I did not yet print out the diagrams you shared a bit ago but with what you may be able to lend from here would be your though on how the wires get from C301 to the dome lights. Any hints will be helpful. I'm almost there and already glad I don't need to buy that module.
(2-Door Utility) Front to rear Body Harness, approx. 34 cm from Front Dome Lamp Breakout, toward C301
Take the bulbs out of the dome light and see if you still have a short to ground on that wire.
Charlie, I know how you feel about issues that cure themselves. I see things the same way. Chances are one of the contacts from one of these lights were touching the body and you cured it by your wiggling and tugging. At least you know if it returns, it is above the headliner. If you press the button that allows you to pay for the answer, there will be an option to add a bonus. That will let you do what you wish. Also, if the problem ever returns, just ask for me, and I'll be happy to help you again. It was a pleasure working with you.