Buick Regal: DTC C028F

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 provide an overview of each diagnostic category.

DTC Descriptors

DTC C028F

Left Park Brake Actuator Circuit

For symptom byte information, refer to: Symptom Byte List.

Diagnostic Fault Information

Circuit/System Description

The Electronic Brake Control Module will diagnose the park brake motor circuits to verify that they are functioning properly. The park brake motor circuits are used to command actuator motor operation, which will apply and release the parking brake. These circuits are used to activate the actuator, which applies or releases pressure on the rear caliper pistons, ultimately applying and releasing the park brake.

When the Park Brake Switch is pulled, a signal is sent to the Electronic Brake Control Module which will supply 12 V to the apply control circuits and ground to the release control circuits which will cause the left and right park brake actuators to activate causing the park brakes to engage. When the Park Brake Switch is pressed, a signal is sent to the Electronic Brake Control Module which will supply 12 V to the released control circuits and ground to the apply control circuits which will cause the left and right park brake actuators to activate causing the park brakes to release.

Conditions for Running the DTC

• Ignition OFF, ACCESSORY, or RUN mode.
• Battery voltage is between 9 - 16 V

Conditions for Setting the DTC

The Electronic Brake Control Module detects a malfunction in the left park brake actuator or its circuits.

Action Taken When the DTC Sets

• The parking brake is disabled, one release allowed.
• A message and/or a warning indicator may be displayed.

Conditions for Clearing the DTC

• The Electronic Brake Control Module will clear the DTC after 40 consecutive ignition on/off cycles with at least one test pass in each ignition cycle and no test fail result.
• The condition for the DTC is no longer present.

Diagnostic Aids

After repairing any fault, the DTC will still be set as current and the park brakes will not function. It is necessary to clear the DTC with a scan tool in order to place the DTC in history and regain park brake function.

Reference Information

Schematic Reference

Park Brake System Wiring Schematics

Connector End View Reference

COMPONENT CONNECTOR END VIEW INDEX

Description and Operation

Electronic Parking Brake Description

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. Verify the M104L Park Brake Actuator - Left apply when pulling the S91 Park Brake Switch.

• If the M104L Park Brake Actuator - Left does not apply

Refer to the Circuit/System Testing.

• Go to next step: If the M104L Park Brake Actuator - Left does apply

2. Verify the M104L Park Brake Actuator - Left release when pressing the S91 Park Brake Switch.

• If the M104L Park Brake Actuator - Left does not release

Refer to the Circuit/System Testing.

• Go to next step: If the M104L Park Brake Actuator - Left does release

3. All OK.

Circuit/System Testing

NOTE: It is necessary to clear the DTC after any repair is made to regain park brake output control and have the DTC to set as history.

1. Ignition OFF, disconnect the harness connector at the M104L Park Brake Actuator - Left and the harness connector at the K17 Electronic Brake Control Module. Ignition ON 2. Test for less than 1 V between the K17 Electronic Brake Control Module harness connector terminals listed below and ground:

• Terminal 12
• Terminal 13
• If 1 V or greater

Repair the short to voltage on the circuit.

• Go to next step: If less than 1 V

3. Ignition OFF.

4. Test for infinite resistance between the K17 Electronic Brake Control Module harness connector terminals listed below and ground:

• Terminal 12
• Terminal 13
• If less than infinite resistance

Repair the short to ground on the circuit.

• Go to next step: If infinite resistance

5. Test for less than 2 Ω between the M104L Park Brake Actuator - Left harness connector terminal 1 and the K17 Electronic Brake Control Module harness connector terminal 13

• If 2 Ω or greater

Repair the open/high resistance in the circuit.

• Go to next step: If less than 2 Ω

6. Test for less than 2 Ω between the M104L Park Brake Actuator - Left harness connector terminal 2 and the K17 Electronic Brake Control Module harness connector terminal 12

• If 2 Ω or greater

Repair the open/high resistance in the circuit.

• Go to next step: If less than 2 Ω

7. Install a 25 A fused jumper wire between one of the control terminals at the M104L Park Brake Actuator - Left and 12 V. Momentarily install a jumper wire between the other control terminal and ground. Reverse the jumper wires at least two times, the M104L Park Brake Actuator - Left should perform the apply and release function.

• If the actuator does not perform the apply and release function

Replace the M104L Park Brake Actuator - Left.

• Go to next step: If the actuator performs the apply and release function

8. Replace the K17 Electronic Brake Control Module.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

• Parking Brake Actuator Replacement (GNC)Parking Brake Actuator Replacement (GNQ)
• Control Module References for control module replacement, programming and setup

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