When the transmission is placed in the reverse position, the engine control module (ECM) sends a serial data message to the body control module (BCM). The message indicates that the gear selector is in the reverse position. The BCM applies battery voltage to the backup lamps. The backup lamps are permanently grounded. Once the driver moves the gear selector out of the reverse position, a message is sent by the ECM via serial data requesting the BCM to remove battery voltage from the backup lamp control circuit.

Schematic Reference

Exterior Lights Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Exterior Lighting Systems Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, perform the Backup Lamps Relay Command test. The backup lamp should be ON/OFF

1. Ignition OFF, disconnect the harness connector at the B16 Backup Lamp Switch.
2. Test for less than 5 Ω between the ground circuit harness connector terminal 2 and ground.

⇒	If greater than the specified value, test the ground circuit for an open/high resistance.

3. Disconnect the X1 harness connector at the K20 Engine Control Module (ECM)
4. ignition On, test for less than 0.3 V at the B16 Backup Lamp Switch signal circuit harness connector terminal 1 and ground.

⇒	If greater then the specified value, test the signal circuit for a short to voltage.

5. Ignition OFF, test for infinite resistance between the B16 Backup Lamp Switch signal circuit harness connector terminal 1 and ground.

⇒	If lower then the specified value, test the signal circuit for a short to ground.

6. Connect the harness connector at the B16 Backup Lamp Switch.
7. Reversing gear engaged, test for less than 5 Ω between the K20 Engine Control Module (ECM) X1 harness connector terminal 71 and ground.

⇒	If greater then the specified value, test the signal circuit for an open/high resistance. If the circuit test normal, test or replace the B16 Backup Lamp Switch.

8. Reversing gear disengaged, test for infinite resistance between the K20 Engine Control Module (ECM) X1 harness connector terminal 71 and ground.

⇒	If lower then the specified value, test or replace the B16 Backup Lamp Switch.

9. If all the circuits test normal, replace the K20 Engine Control Module (ECM).

Static Test

1. Ignition OFF, disconnect the harness connector at the B16 Backup Lamp Switch. Reversing gear engaged, test for less than 5 Ω at the B16 Backup Lamp Switch terminal 1 and terminal 2.

⇒	If greater than the specified value replace the B16 Backup Lamp Switch.

2. Reversing gear disengaged, test for infinite resistance at the B16 Backup Lamp Switch terminal 1 and terminal 2.

⇒	If less than the specified value replace the B16 Backup Lamp Switch.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.