Schematic Reference: Exterior Lights Schematics

Connector End View Reference: Master Electrical Component List in Wiring Systems

1

Did you perform the Lighting System Diagnostic System Check?

Go to Step 2

Go to Symptoms - Lighting Systems

1. Block the wheels and set the parking brake.
2. Turn ON the ignition, with the engine OFF.
3. Place the gear selector in and out of the reverse position.

Do the backup lamps operate properly?

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3

1. Turn ON the ignition, with the engine OFF.
2. Move the gear selector in and out of the reverse gear position.

Does the reverse lamp relay turn ON and OFF with the gear selector's position?

Go to Step 4

Go to Step 5

1. Turn OFF the ignition.
2. Disconnect the reverse relay. Refer to Relay Replacement in Wiring Systems.
3. Turn ON the ignition, with the engine OFF.

Do the backup lamps turn OFF?

Go to Step 5

Go to Step 7

1. Turn OFF the ignition.
2. Connect a test lamp between the reverse relay control side supply voltage circuit and the reverse lamp relay control circuit.
3. Turn ON the ignition, with the engine OFF.
4. Move the gear selector in and out of reverse gear position.

Does the test lamp turn ON and OFF in with the gear selector's position?

Go to Step 8

Go to Step 6

Test the reverse lamp relay control circuit for a short ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 12

Go to Step 9

Test the backup lamp supply voltage circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 12

Go to Step 8

Inspect for poor connections at the reverse lamp relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 12

Go to Step 10

Inspect for poor connections at the harness connector of the transmission control module (TCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 12

Go to Step 11

Replace the reverse relay. Refer to Relay Replacement in Wiring Systems.

Did you complete the replacement?

Go to Step 12

--

Replace the TCM. Refer to Transmission Control Module Replacement in Automatic Transmission - Allison.

Did you complete the replacement?

Go to Step 12

--

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2