Backlight Dimming RX Failure (MTC)

BACKLIGHT DIMMING RX FAILURE (MTC)

For a complete wiring diagram Consult Diagrams/Electrical

- When Monitored:
With the ignition on.

- Set Condition:
If the A/C Heater Control fails to receive the Dimming message from the Body Control Module (BCM) for more than 5 seconds. This fault will cause the mode switch status indicators on the A/C Heater Control to default to the daytime brightness setting.





Diagnostic Test

1. VERIFY DTC IS ACTIVE
Turn the ignition on.
With the scan tool, check for DTCs.
Does the scan tool display this DTC as active?

Yes

- Go To 2

No

- The condition that caused this symptom is currently not present. Check for an intermittent condition by inspecting the related wiring harness for chafed, pierced, pinched, and partially broken wires. Also, inspect the related connectors for broken, bent, pushed out, spread, corroded, or contaminated terminals. Repair as necessary.
- Perform BODY VERIFICATION TEST - VER 1. Body Verification Test.

2. VERIFY BCM IS ACTIVE ON THE BUS
With the scan tool, verify that the BCM is active on the Bus.
Is the BCM active on the Bus?

Yes

- Go To 3

No

- Communications - Verbose Codes for No Response related diagnostic procedures.

3. CHECK FOR DTCs
With the scan tool, read DTCs.
Does the scan tool display any DTCs?

Yes

- Diagnose and repair the DTC(s).
- Perform the BODY VERIFICATION TEST - VER 1. Body Verification Test.

No

- Go To 4

4. CHECK DIMMING FUNCTION AT A/C HEATER CONTROL
NOTE: Make sure that the Panel Dimmer switch is not in set in Funeral Mode.

NOTE: It may be necessary to shade the front of the A/C Heater Control in order to see a change in the backlighting.

Turn the park lamps on.
Rotate the Panel Dimmer switch in both directions while watching the A/C Heater Control.
Does the backlighting dim & brighten with respect to the dimmer switch position?

Yes

- No problem found at this time.
- Perform BODY VERIFICATION TEST - VER 1. Body Verification Test.

No

- Go To 5

5. CHECK DIMMING FUNCTION AT RADIO

NOTE: Make sure that the Panel Dimmer switch is not in set in Funeral Mode.

Turn the park lamps on.
Press the Radio's power switch on.
Rotate the Panel Dimmer switch in both directions while watching the radio display.
Does the display dim & brighten with respect to the dimmer switch position?

Yes

- Using the schematics as a guide, check the A/C Heater Control pins, terminals, and connectors for corrosion, damage, and terminal push out. Pay particular attention to all Communication, Power, and Ground circuits. If no problems are found, replace the A/C Heater Control.
- Perform BODY VERIFICATION TEST - VER 1. Body Verification Test.

No

- Using the schematics as a guide, check the BCM pins, terminals, and connectors for corrosion, damage, and terminal push out. Pay particular attention to all Communication, Power, and Ground circuits. If no problems are found, replace and program the BCM.
- Perform BODY VERIFICATION TEST - VER 1. Body Verification Test.