DRLs Inoperative After BCM Replacement - keywords B2650 beam DTC head headlamp high highbeam lamp light low lowbeam

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in the PI.

2005 Chevrolet Impala or Monte Carlo with inoperative DRLs and/or a current B2650 after replacing the BCM.

The DRL operation has changed on the 2005 Impala and Monte Carlo. The 2000-2004 Chevrolet WBs used the high beam headlamps at reduced intensity for DRL operation. On the 2005 Chevrolet WB, the low beam headlamps are used for DRL operation.

Description and Operation of the DRLs on the 2005 Impala and Monte Carlo:

The ambient light sensor is a light-sensitive transistor that varies its voltage signal to the body control module (BCM) in response to changes in the outside (ambient) light level. When the BCM receives this signal, the BCM either turns on just the low beam headlamps for the daytime running lamp (DRL) operation or turns on the low beam headlamps and the exterior lamps for automatic lamp control (ALC). Any function or condition that turns on the headlamps will cancel the DRL operation. Thirty seconds after you start the engine with the headlamp switch in the OFF position, the DRL will perform one of two actions:

1. Illuminate the LOW BEAM headlamps in daylight conditions.
2. Illuminate the LOW BEAM headlamps and exterior park lamps for low light conditions.

The DRL/EXT Fuse in the top underhood junction block supplies battery positive voltage at all time to the coil side of DRL relay, left low and high beam headlamps. When the DRL ambient light sensor indicates a daylight condition, the BCM energizes the DRL relay allowing ground from G101 through the switched side of the DRL relay to the left and right low beam headlamps. The DRL operates when the ignition switch is in the RUN position, the parking brake is not set and the transmission is not in the PARK position. When these conditions are met and the DRL ambient light sensor indicates daylight conditions, the DRL will illuminate.

Since the 2005 Chevrolet Impala and Monte Carlo use the low beam headlamps for the DRL operation, they also use a different BCM. If after replacing the BCM, DTC B2650 sets current, verify the correct BCM part number is being used.

Please follow this diagnosis 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.