Wet Headlamp Causing Problems

Dec. 18, 2019

This bulletin applies to 2019 GMC 1500 Limited and 2016-2018 Sierra vehicles. Issues may involve any of the following:

  • - No crank
  • - Dead battery
  • - Crank/no start
  • - Unable to SPS program ECM
  • - DTC P1682, P129D, P10E4 or P2535

While performing diagnostics, voltage may be found on any one of the following underhood electrical center fuses with the ignition off: F26UA, F31UA, F34UA, F39UA, F40UA or F56UA. These fuses are switched ignition and should not have any voltage with the ignition off. This can cause multiple modules to stay awake and never go to sleep, causing a dead battery. These concerns can be intermittent and may be more apparent during wet weather conditions.

The cause may be water intrusion into either of the headlamp assemblies or the headlamp assembly connections. Inspect each headlamp assembly for water intrusion. If water intrusion is found, disconnect the appropriate headlamp assembly and evaluate the condition. If the condition is alleviated, replace the headlamp assembly. If disconnecting the headlamp assembly does not alleviate the condition, check for water intrusion in the headlamp assembly connections and repair as necessary.