DTC B1991
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. DTC Descriptor DTC B1991 Stop Lamp Relay Coil Control Refer to Symptom Byte List for symptom byte information. Diagnostic Fault Information
| Circuit | Circuit Descriptio | Short to n Ground | Open/High Resistance | Short to Voltage | Signal Performan |
|---|---|---|---|---|---|
| 820 | Control | B1991 11 | 1 | 1 | — |
| 2050 | Ground | — | 1 | — | — |
| 1. Center High Mounted Stop Lamp Malfunction |
Scan Tool Functions K219 Lighting Control Module – Control Functions – Exterior Lighting
| Control Function | Description |
|---|---|
| Center High Mounted Stop Lamp | This control function will control the center high mounted stop lamp ON/OFF |
Circuit/System Description The B22 Brake Pedal Position Sensor is used to sense the action of the driver application of the brake pedal. When the variable signal reaches a voltage threshold indicating the brakes have been applied, the K9 Body Control Module (BCM) sends a serial data message to the K219 Lighting Control Module to illuminate the stop lamps. The Lighting Control Module responds by applying voltage to the left and right stop lamp control circuits as well as the center high mounted stop lamp (CHMSL) control circuit 820 illuminating the left and right stop lamps and the CHMSL. The CHMSL control circuit 820 is also connected the K68 Trailer Lamp Control Module for additional brake pedal applied input. Conditions for Running the DTC Battery voltage must be between 9–16 V. Brakes APPLIED. Conditions for Setting the DTC The Lighting Control Module detects a short to ground on circuit 820. Actions Taken When the DTC Sets The center high mounted stop lamp (CHMSL) will be inoperative. Conditions for Clearing the DTC The condition responsible for setting the DTC no longer exists. A history DTC will clear once 40 malfunction-free ignition cycles have occurred. Reference Information Schematic Reference Exterior Lights Schematics Connector End View Reference Master Electrical Component List 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 Testing
- Ignition OFF, disconnect the connector at the E6 High Mount Stop Lamp.
- Verify a test lamp illuminates between ground circuit terminal 1 and B+. ⇒ If the test lamp does not illuminate 2.1. Repair the open/high resistance circuit 2050 or ground connection. ⇓ If the test lamp illuminates
- Connect a test lamp between control circuit terminal 2 and ground, ignition ON.
- Verify the test lamp turns ON and OFF when commanding the Center High Mounted Stop Lamp ON and OFF with a scan tool. ⇒ If the test lamp is always OFF 4.1. Test circuit 820 for a short to ground. ⇒ If a short to ground is found, repair the fault on the circuit. ⇓ If a short to ground is not found 4.2. Test circuit 820 for an open/high resistance. ⇒ If an open/high resistance is found, repair the fault on the circuit. ⇓ If an open/high resistance is not found 4.3. Replace the K219 Lighting Control Module. ⇒ If the test lamp is always ON 4.1. Test circuit 820 for a short to voltage. ⇒ If a short to voltage is found, repair the fault on the circuit. ⇓ If a short to voltage is not found. 4.2. Replace the K219 Lighting Control Module. ⇓ If the test lamp turns ON and OFF
- Replace the E6 High Mount Stop Lamp. Repair Instructions Perform the Diagnostic Repair Verification after completing the repair. Lighting Component Replacement Reference Control Module References for BCM replacement, programming, and setup