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Home >> Chevrolet >> 2020 >> Express 2500 LS, 6.0L Eng VIN G >> Repair and Diagnosis >> External Pages >> Different car >> Section 18 (Lighting System) >> Diagnostic Information and Procedures >> Stop Lamps Malfunction >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2019 GMC Savana 3500, 2019 GMC Savana 2500, 2019 Chevrolet Express 3500, and 2019 Chevrolet Express 2500. However, it is still accessible from the selected car via links, so may be relevant.

Brake Pedal Position Sensor Malfunction

  1. Ignition OFF, disconnect the harness connector at the B22 Brake Pedal Position Sensor, ignition ON.
  2. Test for less than 1 V between the low reference circuit terminal 1 and ground.
    • If 1 V or greater 
    1. Ignition OFF, disconnect the X1 harness connector at the K9 Body Control Module, ignition ON.
    2. Test for less than 1 V between the low reference circuit and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • If less than 1 V, replace the K9 Body Control Module.
    • Go to next step: If less than 1 V 
  3. Test or replace the B22 Brake Pedal Position Sensor.

Stop Lamp Malfunction (cargo/passenger)

  1. Ignition OFF, disconnect the harness connector at the appropriate stop lamp.
  2. Ignition OFF, exterior lamps OFF, test for less than 5 Ω between the ground circuit terminal G and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Connect a test lamp between the control circuit terminal A and ground.
  4. Turn 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 selected states.
    • If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.
    • 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, replace the BCM.
  5. If all circuits test normal, test or replace the stop lamp.

Center High Mount Stop Lamp Malfunction (cargo/passenger)

  1. Ignition OFF, disconnect the harness connector at the center high mount stop lamp.
  2. Ignition OFF, test for less than 5.0 Ω between the ground circuit terminal B and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Connect a test lamp between the control circuit terminal A and the ground.
  4. Ignition ON, apply and release the brake pedal. The test lamp should turn ON and OFF as the brake pedal is applied and released.
    • If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.
    • 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, replace the BCM.
  5. If all circuits test normal, replace the center high mount stop lamp.

Stop Lamp Relay Malfunction (cutaway)

  1. Ignition OFF, disconnect the X5 harness connector at the BCM.
  2. Ignition OFF, verify that a test lamp does not illuminate between the control circuit terminal 5 and round.
    • If the test lamp illuminates, test the control circuit for a short to voltage.
  3. Ignition ON, connect a 3 A fused jumper wire between the control circuit terminal 5 and B+. Verify the auxiliary stop lamps illuminate.
    • If the stop lamps do not illuminate, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the underhood fuse block.
  4. If all circuits test normal, replace the BCM.
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