C027B

DTC C027B

Diagnostic Instructions

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

DTC Descriptor
DTC C027B 00
- Brake Booster Electric Vacuum Pump Malfunction

Diagnostic Fault Information






Circuit/System Description

The brake booster vacuum sensor measures the vacuum in the brake booster assembly. The electronic brake control module (EBCM) supplies a 5 V reference and a low reference circuit to the brake booster vacuum sensor. The vacuum sensor supplies a voltage signal in relation to the pressure in the brake booster to the EBCM. When the vacuum within the system drops, the EBCM turns ON the vacuum pump by providing ground to the vacuum pump relay. The relay activates and supplies voltage to the brake booster pump motor.

Conditions for Running the DTC

Ignition ON

Conditions for Setting the DTC

The EBCM detects a vacuum leak.

Action Taken When the DTC Sets

The brake warning indicator turns ON.

Conditions for Clearing the DTC

* A current DTC clears when the diagnostic runs and passes.
* The EBCM will turn OFF the indicator in the next ignition cycle.

Reference Information
Schematic Reference

Hydraulic Brake Schematics [1][2]Electrical Diagrams
Connector End View Reference

Component Connector End Views Connector End Views By Name
Description and Operation

Brake Assist System Description and Operation Brake Assist System
Electrical Information Reference

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

Scan Tool Reference

Control Module References Control Module References for scan tool information

Circuit/System Verification

1. Ignition OFF, apply and release the brake pedal several times to ventilate the brake booster.
2. Engine running, the M9 Brake Booster Pump Motor should turn ON for a short time.

Circuit/System Testing

1. Inspect the brake booster vacuum system for damage, leakage and correct installation. Refer to Brake Assist System Diagnosis Component Tests and General Diagnostics.
2. If the brake booster vacuum systems diagnoses normal, ignition OFF, disconnect the KR14 Brake Booster Pump Motor Relay.
3. Verify a test lamp illuminates between the B+ circuit terminal 5 X1 and ground.

• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the X50A Fuse Block - Underhood.

4. Test for less than 5 ohm between the ground circuit terminal 1 X1 and ground.

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

5. Verify that a test lamp does not illuminate between the control circuit terminal 2 X1 and ground.

• If the test lamp illuminates, test the control circuit for a short to voltage. If the circuit tests normal, replace the K17 Electronic Brake Control Module.

6. Connect a 10 A fused jumper wire between KR14 Brake Booster Pump Motor Relay B+ circuit terminal 1 X2 and B+. Connect a 10 A fused jumper wire between KR14 Brake Booster Pump Motor Relay ground circuit terminal 2 X2 and ground. Verify that the M9 Brake Booster Pump Motor activates.

• If the M9 Brake Booster Pump Motor is not active, test the KR14 Brake Booster Pump Motor Relay ground circuit terminal 2 X2 and the control circuit terminal 1 X2 for an open/high resistance. If the circuit tests normal, replace the M9 Brake Booster Pump Motor.

7. Remove all fused jumper wires. Connect the KR14 Brake Booster Pump Motor Relay to the harness connector. Disconnect the harness connector at the K17 Electronic Brake Control Module. Connect a 10 A fused jumper wire between the K17 Electronic Brake Control Module circuit terminal 26 and B+.
8. Verify that the M9 Brake Booster Pump Motor activates.

• If the M 9 Brake Booster Pump Motor is not active, replace the KR14 Brake Booster Pump Motor Relay.

9. If all circuits test normal, replace the K17 Electronic Brake Control Module.

Component Testing

Vacuum Pump Motor Test
1. Ignition OFF, disconnect the harness connector at the KR14 Brake Booster Pump Motor Relay.
2. Connect a 20 A fused jumper wire between the B+ circuit terminal 1 X2 and B+.
3. Connect a 10 A fused jumper wire between the control terminal 2 X2 and ground.

• If the M9 Brake Booster Pump Motor does not activate, replace the M9 Brake Booster Pump Motor.

Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.

* Power Brake Booster Vacuum Sensor Replacement Service and Repair
* Power Vacuum Brake Booster Replacement Service and Repair
* Control Module References Control Module References for EBCM replacement, programming and setup