8042CF

What the Code Means

Code 8042CF (B0042CF) points to a fault in the front interior light button circuit. The system detects that the button is either mechanically stuck (not returning to its rest position) or has a short in the electrical circuit.

Interior lighting is controlled by the body control module (such as FRM or BDC) through the corresponding button. When the button sticks or shorts, the module logs a signal mismatch and stores the fault code. This is an electrical fault of moderate severity.

Symptoms

• The front interior light button sticks or has a short (per the source data).
• Interior lighting may misbehave: the light may not turn on, may not turn off, or may operate erratically.
• Fault indication on the instrument cluster or in the control module.

Diagnosis and Repair

Step 1: Check the Button

• Inspect the front interior light button for mechanical sticking, contamination, or damage.
• Check that it moves freely and returns to its rest position.

Step 2: Check the Electrical Circuit

• Use a multimeter to check the button circuit for a short.
• Test the wiring from the button to the control module (FRM/BDC) for an open or a short to ground.

Step 3: Diagnose with ISTA/INPA

• Read the fault codes and check the button status in the control module.
• Use the test functions to check how the lighting responds to a button press.

Step 4: Repair

• If the button is mechanically stuck, clean or replace it.
• If there's a short, restore the wire insulation or replace the damaged section of the harness.
• If the fault is in the control module, it may need to be replaced or reprogrammed.

Note

The source data contains general bumper repair recommendations that don't apply to this fault and are not included in the description.

Secondary Issues

If you ignore the front interior light button fault, you may see:

• Battery drain from a short or from the light staying on.
• Damage to the body control module (FRM/BDC) from a prolonged short.
• Loss of interior lighting, which can reduce comfort and safety (especially after dark).

Fix the fault promptly to avoid more serious consequences.