2013 Silv 2500HD No DRL/AHL

[CoRifleman]

Going to cross post this in hopes I can square this away - I apologize if this is the wrong spot and will remove it if necessary.

 

Just bought a fleet 2013 Silverado 2500HD.  When I first got it, the ambient light sensor cover was broken off, ie sensor exposed.

 

Neither the DRL or AHL seem to work.

 

I can manually turn on the headlamps and they work fine.

 

The truck does NOT have RPO T61 (DRL), but also does NOT have RPO T62 (DRL Delete).  It DOES have RPO T74 (Auto Headlamp / Delay).

 

I've replaced the ambient light sensor with the new GM part number (the original number was superceded).

 

Troubleshooting:

 

I verified that if I ground BCM connector X4 (Black), pin 23 (l-gn/bk), the DRLs come on.  Which means all wiring in the fuse box, the on board pcb relay, and wiring to the fuse box are good.  To me, that leaves the inputs needed to energize the relay in the BCM (ambient sensor, in-gear, no ebrake) or the BCM programming.

 

As best I can tell, the gear selector and ebrake trigger/sensors work correctly.

 

Regarding the AHL, I went to the headlamp switch and verified that the L-BU (parking), D-Gn (OFF), and WH (Headlamp) lines all rest at 12v and drop to 0 when the switch is on their position.

 

Any ideas?