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 (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 (Programming and Relearning) 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 (Brake Assist System Diagnosis).
2. If the brake booster vacuum systems diagnoses normal, disconnect the harness connector at the M9 Brake Booster Pump Motor.
3. Ignition OFF, test for less than 5 ohm between the ground circuit terminal 2 and ground.
• If greater than the specified value, test the ground circuit for an open/high resistance.
4. Disconnect the KR28 Vacuum Pump Relay.
5. Ignition ON, verify that a test lamp illuminates between the circuit terminals listed below and ground.
* Relay coil ignition terminal 86
* Relay switch ignition terminal 87
• If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
6. Verify that a test lamp does not illuminate between the relay controlled output circuit terminal 30 and ground.
• If the test lamp illuminates, test the controlled output circuit for a short to voltage.
7. Verify that a test lamp does not illuminate between the relay control circuit terminal 85 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 (EBCM).
8. Ignition OFF, connect the harness connector at the M9 Brake Booster Pump Motor.
9. Momentarily connect a 20 A fused jumper wire between the vacuum pump relay controlled output circuit terminal 30 and B+. Verify the M9 Brake Booster Pump Motor activates.
• If the M9 Brake Booster Pump Motor does not activate and the vacuum pump motor fuse is open, test the controlled output circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the M9 Brake Booster Pump Motor.
10. Disconnect the harness connector at the K17 Electronic Brake Control Module (EBCM).
11. Test for infinite resistance between the vacuum pump relay control circuit terminal 85 and ground.
• If less than the specified value, test the control circuit for a short to ground.
12. Connect the KR28 Vacuum Pump Relay.
13. Engine running, momentarily connect a fused jumper wire between the control circuit terminal 35 and ground. Verify the M9 Brake Booster Pump Motor activates.
• If the M9 Brake Booster Pump Motor does not activate, test the vacuum pump relay control circuit for an open/high resistance. If the circuit tests normal, test or replace the KR28 Vacuum Pump Relay.
14. If all circuits test normal, replace the K17 Electronic Brake Control Module (EBCM).
Component Testing
Vacuum Pump Motor Test
1. Ignition OFF, disconnect the harness connector at the M9 Brake Booster Pump Motor.
2. Connect a 20 A fused jumper wire between the control circuit terminal 1 and B+.
3. Connect a jumper wire between the ground circuit terminal 2 and ground, verify the M9 Brake Booster Pump Motor activates.
• If the M9 Brake Booster Pump Motor does not activate, replace the M9 Brake Booster Pump Motor.
Relay Test
1. Ignition OFF, disconnect the KR28 Vacuum Pump Relay.
2. Test for 60-100 ohm between terminals 85 and 86 of the relay.
• If not within the specified range, replace the KR28 Vacuum Pump Relay.
3. Test for infinite resistance between the following terminals:
* 30 and 85
* 30 and 86
* 30 and 87
• If less than the specified value, replace the KR28 Vacuum Pump Relay.
4. Install a fused jumper wire between relay terminal 86 and B+. Install a jumper wire between relay terminal 85 and ground.
5. Test for less than 5 ohm between terminals 30 and 87.
• If greater than the specified value, replace the KR28 Vacuum Pump Relay.
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 (Programming and Relearning) for EBCM replacement, setup and programming