GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 2008 🢒 Isuzu MD F-Series 🢒 Body Systems 🢒 Lighting 🢒 Stop Lamps Malfunction

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

B+ -- Stop Lamp Switch

1

1

--

--

Brake Switch Signal

1

1

2

--

Stop Lamp Supply Voltage

1

1

2

--

Stop Lamp Switch Control Circuit

1

1

2

--

1. Stop lamps are inoperative

2. Stop lamps are always ON

Circuit/System Description

Stop Lamps

Battery voltage is supplied at all times to the stop lamp switch and the turn signal hazard flasher module from Circuit Breaker 25 located in the I/P fuse block-2. When the brake pedal is pressed, battery voltage is applied through the stop lamp switch and the stop lamp switch signal circuit to the turn signal hazard flasher module. In response to this signal, the module applies battery voltage through the turn stop lamp control circuits illuminating the stop lamps.

Trailer Stop Lamps

Battery voltage is supplied at all times to the trailer stop lamp switch from Circuit Breaker 25 located in the I/P fuse block-2. Battery voltage is also supplied at all times to the TRAILER STOP LAMP Relay from Fuse 14 located in fuse block-2. Ground for the relay is provided at G400. When the brake pedal is pressed, battery voltage is applied through the stop lamp switch and the stop lamp switch signal circuit to the trailer stop lamp relay energizing the relay. With the relay energized, battery voltage is applied through the through the turn stop lamp control circuits illuminating the trailer stop lamps.

Reference Information

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

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification
  1. Ignition ON, verify that all turn signals operate.
    2. ⇒If the turn signals are inoperative, refer to Turn Signal Lamps and/or Indicators Malfunction .

Observe the operation of stop lamps, while applying the brake pedal. Stop lamps should illuminate.

⇒If both stop lamps are always OFF or remain always ON, refer to Stop Lamp Assembly Malfunction.
⇒If a single stop lamp is always OFF or remains always ON, refer to Single Stop Lamp Assembly Malfunction.
⇒If just the trailer stop lamps are always OFF or remain always ON, refer to Trailer Stop Lamps Malfunction.

Circuit/System Testing

Stop Lamp Assembly Malfunction

  1. Ignition OFF, disconnect the stop lamp switch.
  2. Ignition ON, verify that a test lamp illuminates between the appropriate B+ circuit terminal listed below and ground.
    3. • RPO JE3 terminal B
    • RPO JE4 terminal D
    ⇒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 the harness connector at the turn signal hazard flasher module.
  4. Connect a test lamp between the control circuit terminal 2 and ground.
  5. Ignition ON, apply and release the brake pedal. The test lamp should turn ON and OFF when the brake pedal is applied and released.
    6. ⇒If the test lamp is always ON, test the signal 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 signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the stop lamp switch.
  6. If all circuits test normal, replace turn signal hazard flasher module.

Single Stop Lamp Malfunction

  1. Ignition OFF, disconnect the inoperative tail lamp assembly.
  2. Test for less than 5.0 ohms between ground circuit terminal E and ground.
    3. ⇒If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Connect a test lamp between control circuit terminal C and ground.
  4. Ignition ON, apply and release the brake pedal. The test lamp should turn ON and OFF when the brake pedal is applied and released.
    5. ⇒If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace turn signal hazard flasher module.
    ⇒If the test lamp is always OFF, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace turn signal hazard flasher module.
  5. If all circuits test normal, test or replace the bulb or tail lamp assembly.

Trailer Stop Lamps Malfunction

  1. Ignition OFF, disconnect the trailer stop lamp switch.
  2. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal A and ground.
    3. ⇒If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.
  3. Ignition OFF, connect the harness connector at the trailer stop lamp switch and disconnect the harness connector at the TRAILER STOP LAMP Relay.
  4. test for less than 5.0 ohms between the ground circuit terminal 85 and ground.
    5. ⇒If greater than the specified range, test the ground circuit for an open/ high resistance.
  5. Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.
    6. ⇒If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open high resistance.
  6. Connect a test lamp between the control circuit terminal 86 and ground.
  7. Ignition ON, apply and release the brake pedal. The test lamp should turn ON and OFF when the brake pedal is applied and released.
    8. ⇒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.
  8. Connect a test lamp between the tractor trailer receptacle terminal 4 and ground.
  9. Connect a 3A fused jumper wire between the relay B+ circuit terminal 30 and the control circuit terminal 87. The test lamp should illuminate.
    10. ⇒If the test lamp does not illuminate, test the control circuit for a short ground or an open/high resistance.
  10. If all circuits test normal, test or replace the trailer stop lamp relay.

Component Testing
  1. Ignition OFF, disconnect the marker lamp relay.
  2. Test for 70-100 ohms between terminals 85 and 86.
    3. ⇒If the resistance is not within the specified range, replace the relay.
  3. Test for infinite resistance between the following terminals:
    4. • 30 and 85
    • 30 and 86
    • 30 and 87
    • 85 and 87
    ⇒If not the specified value, replace the relay.
  4. Test for less than 2 ohms between terminals 30 and 87A.
    5. ⇒If greater than the specified range, replace the relay.
  5. Install a 20A fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms of resistance between terminals 30 and 87.
    6. ⇒If greater than the specified range, replace the relay.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Stop Lamp Switch Replacement
    •  Tail Lamp Replacement
    •  Relay Replacement