Circuit/System Testing

Dimmer Switch Malfunction

1. Ignition OFF, disconnect the harness connector at the headlamp and panel dimmer switch.
2. Ignition OFF, verify that a test lamp illuminates between the ground circuit terminal 8 and B+.
   • If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
3. Ignition ON, verify the scan tool Dimming Control Signal parameter is less than 0.1 volts.
   • If greater than the specified range, test the signal circuit terminal 13 for a short to voltage. If the circuit tests normal, replace the BCM.
4. Ignition ON, test for B+ between the I/P dimming voltage reference circuit terminal 15 and ground.
   • If less than the specified value, test the voltage reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
5. Install a 3A fused jumper wire between the signal circuit terminal 13 and the voltage reference circuit terminal 15. Verify the scan tool BCM Dimming Control Signal parameter is greater than 2.6 volts.
   • If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
6. If all circuits test normal, test or replace the headlamp and panel dimmer switch.

Interior Backlighting Malfunction

1. Ignition OFF, disconnect the harness connector at the appropriate component.
2. Ignition OFF, verify that a test lamp illuminates between the listed ground circuit terminal and B+.
   • Rear window switch terminal F
   • Headlamp switch terminal 8
   • Transfer case control switch terminal 6
   • Sunroof switch terminal 5
   • Roof beacon switch terminal 1
   • Garage door opener switch terminal 3
   • Folding seat switch terminal 4
   • Power liftgate open/close switch terminal C
   • Auxiliary HVAC control module terminal 2
   • If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
3. Connect a test lamp between the listed backlighting control circuit terminal and ground.
   • Rear window switch terminal B
   • Headlamp switch (Chevy, GMC) terminal 7
   • Transfer case control switch terminal 5
   • Sunroof switch terminal 3
   • Roof beacon switch terminal 2
   • Garage door opener switch terminal 2
   • Folding seat switch terminal 5
   • Power liftgate open/close switch terminal B
   • Auxiliary HVAC control module terminal 1
4. Command the dimming test high to low with a scan tool. The test lamp should turn from bright to dim when changing between the commanded states.
   • If the test lamp is always OFF, test the control circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the BCM.
   • If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.
5. If all circuits test normal, test or replace the appropriate component.

LED Dimming Malfunction

1. Ignition OFF, disconnect the harness connector at the appropriate component.
2. Ignition OFF, verify that a test lamp illuminates between the listed ground circuit terminal and B+.
   • Left steering wheel switch terminal 8
   • Right steering wheel switch terminal 1
   • Headlamp and Panel Dimmer Switch (Cadillac) terminal 8
   • Analog clock terminal 2
   • DIC switch terminal 5
   • Manual HVAC control module terminal 10 X2
   • Multifunction accessory switch (Chevy, GMC) terminal 3
   • Multifunction accessory switch (Cadillac w heated windshield washer and power running boards) terminal 1
   • Multifunction accessory switch (Cadillac w StabiliTrak® and rear park assist) terminal 5
   • If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
3. Connect a test lamp between the listed LED dimming control circuit terminal and ground.
   • Left steering wheel switch terminal 6
   • Right steering wheel switch terminal 2
   • Headlamp and Panel Dimmer Switch (Cadillac) terminal 7
   • IPC (Chevy, GMC) terminal 8
   • Radio terminal 7 X1
   • Analog clock terminal 3
   • Rear seat audio controller terminal 7 X1
   • DIC switch terminal 4
   • Manual HVAC control module terminal 1 X2
   • Multifunction accessory switch (Chevy, GMC) terminal 4
   • Multifunction accessory switch (Cadillac w heated windshield washer and power running boards) terminal 3
   • Multifunction accessory switch (Cadillac w StabiliTrak® and rear park assist) terminal 6
4. Command the dimming test high to low with a scan tool. The test lamp should turn from bright to dim when changing between the commanded states.
   • If the test lamp is always OFF, test the control circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the BCM.
   • If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.
5. If all circuits test normal, test or replace the appropriate component.

Front Door Switch Backlighting Malfunction

1. Ignition OFF, disconnect the harness connector X4 at the door lock and side window switch.
2. Connect a 3A fused jumper wire between the low reference circuit terminal 4 and ground.
3. Connect a test lamp between the backlight supply voltage circuit terminal 13 and B+. The heated seat switch backlighting should illuminate.
   • If the switch backlighting does not illuminate, replace the heated seat switch.
4. If the switch backlighting tests normal, replace the door lock and side window switch.