Battery voltage is supplied at all times to the stop lamp switch from the STOP Fuse 1 or the Circuit Breaker 1 located in the I/P-1 fuse block. When the brake pedal is pressed, B+ is applied through the stop lamp switch and the supply voltage circuits to the coil and switch sides of the CHMSL relay. With the relay energized, B+ is applied through the switch side of the relay and the supply voltage circuit to the turn signal multifunction switch. This voltage is passed through the turn signal switch and the left and right rear stop/turn lamp supply voltage circuits to the tail light assemblies illuminating the stop lamps. Ground for the CHMSL relay is provided at G103. While ground for the left and right tail lamp assemblies is provided at G203.

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

1. Command turn signal lamps ON and OFF using the turn signal multifunction switch. The left and right turn signals should turn ON and OFF when changing between the commanded states.

⇒	If the system does not perform as specified, refer to Turn Signal Lamps and/or Indicators Malfunction.

2. Observe the operation of the stop lamps while pressing and releasing the brake pedal. Stop lamps should turn ON and OFF between the commanded states.

⇒	If the stop lamps are always OFF or remain ON, refer to Circuit/System Testing.

1. Ignition OFF, disconnect the harness connector at the stop lamp switch.
2. Ignition ON, verify that a test lamp illuminates between the appropriate B+ circuit terminal listed below and ground.

•	Terminal E (C4 +JE3 or C7/C8 +JE4)

•	Terminal B (C5/C6/C7 +JE3)

⇒	If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

3. Ignition OFF, connect the harness connector at the stop lamp switch and disconnect CHMSL Relay.
4. Test for less than 5.0 ohms between the ground circuit terminal G85 and ground.

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

5. Connect a test lamp between the control circuit terminal G30 and ground.
6. Ignition ON, command the stop lamps ON and OFF by pressing and releasing the brake pedal. The test lamp should turn ON and OFF when changing between the commanding states.

⇒	If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, test or replace the stop lamp switch.

⇒	If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the stop lamp switch.

7. Connect a test lamp between the control circuit terminal G86 and ground.
8. Ignition ON, command the stop lamps ON by pressing the brake pedal. The test lamp should illuminate.

⇒	If the test lamp does not illuminate, test the control circuit for a short to ground or an open/high resistance.

9. Connect a 10A fused jumper wire between the control circuit terminal G30 and the control circuit terminal G87.
10. Verify that the stop lamps illuminate while pressing the brake pedal.

⇒	If the stop lamps do not illuminate, test the control circuit terminal G87 for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the turn signal multifunction switch.

11. If all circuits test normal, test or replace the CHMSL relay.

Stop Lamp Switch

1. Ignition OFF, disconnect the harness connector at the stop lamp switch.
2. Test for infinite resistance between the appropriate B+ circuit terminal and control circuit terminal listed below with the switch in the open position.

•	Terminal E and terminal F (C4 +JE3 or C7/C8 +JE4)

•	Terminal B and terminal A (C5/C6/C7 +JE3)

⇒	If not the specified value, replace the stop lamp switch.

3. Test for less than 2.0 ohms between appropriate B+ circuit terminal and the control circuit terminal listed below with the switch in the closed position.

•	Terminal E and terminal F (C4 +JE3 or C7/C8 +JE4)

•	Terminal B and terminal A (C5/C6/C7 +JE3)

⇒	If greater than the specified range, replace the stop lamp switch.

Relay

1. Ignition OFF, disconnect the relay.
2. Test for 70-100 ohms between terminals 86 and 85.

⇒	If the resistance is not within the specified range, replace the appropriate relay.

3. Test for infinite resistance between the following terminals:

•

30 and 86

•

30 and 87

•

30 and 85

•

85 and 87

⇒	If not the specified value, replace the relay.

4. Install a 10A fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 5.0 ohms between terminals 30 and 87.

⇒	If greater than the specified range, replace the relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.