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Old 06-18-2022, 02:24 PM   #1
tid.smed
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Wrench 2003 L200 dash light issue

Good day! Looking for any advise on the following issue with my 2003 L200.

The dash lights do not work correctly.

With the stalk switch in "auto" and sunlight available, the DRL's are on, the odometer backlight works, the radio and automatic lights are all lit. Covering the sensor, everything goes out except the odometer backlight which can be adjusted fairly reliably (very little dropping out) with the dimmer switch.

With the stalk in DRL or headlights on, the dash lights are all off.

Things I have tried, replacing the stalk switch, verifying all of the exterior lights are working as expected, looking at the fuses (though since most of the interior lights will work in the "auto" daytime setting I think that not to be the issue anyway), Unplugging & re seating the BCM, headlight switch and dimmer switch.

Also the dash lights come on if they are provided a signal, so the bulbs are not burned out.

Anyone got any big ideas?
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Old 06-18-2022, 05:27 PM   #2
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2003 L-Series 3.0L Sedan
Default Re: 2003 L200 dash light issue

If I'm not mistaken, the drawings below apply to your '03 L200 (from my '03 L200/L300 service manuals). Inside the yellow box are the IP indicators, driven by the bcm via pulse width modulated signals (digital voltages controlling lamp output).

1-The dash lamps use the dimmer to control lighting and this dimmer is prone to intermittently acting up. When worn, panel lighting can become erratic by merely touching the dimmer thumbwheel. I can touch mine and dimming drops dramatically. Exercising the thumbwheel up and down tends to clean up internal oxidation. Try this and see if yours does the same.

2-Presuming wiring isn't corroded or damaged (from bcm to IPC), ground may be an issue. A ground splice pack (several around the car) is a small plastic sleeve covering several spade terminal lugs on one end with a large (10 ga?) ring terminal on the other end, mounted to a chassis stud. Several (black) ground wires from various circuits terminate into these splice packs to provide grounding for circuits.
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File Type: jpg L200 IPC2.jpg (84.6 KB, 9 views)
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Old 06-19-2022, 10:45 AM   #3
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Default Re: 2003 L200 dash light issue

This is really great information, thanks! Do you happen to know where the IP ground is located on the body?
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Old 06-19-2022, 10:58 AM   #4
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Default Re: 2003 L200 dash light issue

Google images of GM ground splice packs for examples. There are severa. I'm not near my manuals to take snapshots for posting. There should be at least one in the interior, perhaps more. One on each side of the foot well area? You may have to remove panels to expose wiring.
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Old 06-19-2022, 02:49 PM   #5
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Default Re: 2003 L200 dash light issue

Been doing some more poking around today and found some information of note.

The headlight switch in "auto" has no connections to ground.
In "DRL" the small blue wire becomes connected and all the background lights go off (with the light sensor exposed everything comes on at full brightness except the dash). However the headlights do their normal thing so the BCM is getting the right signals it seem from this input.

The dimmer adjusts the background of the odometer correctly, though from the very helpful diagram above it seems to be on a "Serial Data (Class 2)" line originating from the BCM different from the dash/radio/general illumination. Giving that this rheostat only has two connections it would seem that the BCM signal from here is also fine.

Giving that all of the general illumination lights work fine (except the rear lights on the dimmer switch which I intend to fix now that it's apart) until the headlights are switched through the stalk OR the sensor is covered I am guessing that the BCM is refusing to put out anything but full signal to the illumination, even though it is getting the signal from the dimmer (as evidenced by the odometer backlight adjusting).

I guess I need to order the wiring diagram if I am going to be able to fix this. Luckily there seems to be one for a reasonable price right now. So while I wait for that to arrive, any other ideas?
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Old 06-19-2022, 05:30 PM   #6
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Default Re: 2003 L200 dash light issue

PWM - pulse width modulation signals from the bcm with the dimmer varying signal feedback to vary backlighting.

The right side schematic indicates serial data enabling indicator leds. This includes switching on/off the odometer backlight. My guess is the odometer light isn't dimmer controlled. I can't be certain of it because the schematic deliberately leaves out detailed info as it would overwhelm anyone unfamiliar with sophisticated electronics and would take up many more volumes than already published. Simplifying wiring diagrams is more expedient to get across signal flow.

There's a DRL relay in the engine fuse panel. Try switching it with another one. Labeling of fuses and relays should be in the cover.
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