Intrument Lights when running DRL Russ on 2004 Chevrolet Express 3500

Russ: I checked the fuses #6, #11, #16, #18,#19, #24 & #46 with an ohm meter all fuses checked ok. No work done recently. However in the past a back up camera was added part of the camera works on the coach battery and part of the camera ckt is connected to the dome light in the cab. Also a tach was added and the back light was connected to the instrument ckt. I don't know if this could effect the instrument lights in the DRL position. Is there a relay that operates when the Body Control Module is operated. I would sure like to figure this problem out. Please give me some other suggestions and I will check and get back to you. Thanks again for your help. I have had the Chevy for about three months and the intrument lights worked in the DRL position when I got the truck. Bill

by in Sacramento, CA on February 12, 2009
1 answer
ANSWER by on February 13, 2009
Here is all I can tell you. The service information (SI) does not show specifically that the IP lights will be on when the daytime running lights are on. SI does show that the IP lights are controlled by the body control module (BCM). When the park or headlights are on, the BCM turns on the backlighting for all components using such. Lighting the IP during DRL operation would be a special, separate function, also controlled by the BCM. There are two ways this could be done and SI does not stay how. 1) Turn on IP lights only in the same manner as when all backlighting is on. 2) The BCM would send a message via the network data line connecting all onboard modules to the IP commanding the IP lights on. I would suspect the 1st option would be the way it is done. At any rate, the BCM is in control here. Something may have failed inside the BCM or something new has been wired into a BCM circuit which is causing the BCM not to function correctly. Looking at BCM functions with a scan tool may or may not help isolate the problem. Sorry I cannot be of more help but the available service information is just not clear on how this particular system works.

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