C027B
Auxiliary Brake Booster Pump Malfunction - 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
- Auxiliary Brake Booster Pump Malfunction
Diagnostic Fault Information
Circuit/System Description
The brake booster vacuum sensor measures the vacuum in the brake booster assembly. When the vacuum within the system drops, the EBCM turns ON the auxiliary brake booster pump by providing ground to the brake booster pump relay. The relay activates and supplies voltage to the auxiliary brake booster pump motor.
Conditions for Running the DTC
Ignition ON
Conditions for Setting the DTC
A short to ground, open/high resistance is detected on the brake booster pump relay control circuit.
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 A/C Compressor Clutch
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 auxiliary brake booster pump motor should turn ON for a short time.
Circuit/System Testing
1. Ignition OFF, remove the brake booster pump relay.
2. Ignition ON, verify that a test lamp does not illuminate between the auxiliary brake booster pump control circuit terminal 87 and ground.
• If the test lamp illuminates, test the auxiliary brake booster pump control circuit for a short to voltage.
3. Test for more than 10 ohms between the auxiliary brake booster pump control circuit terminal 87 and ground.
• If less than the specified range, test the auxiliary brake booster pump control circuit for a short to ground.
4. Verify that a test lamp illuminates between the brake booster pump relay switch B+ circuit terminal 30 and ground.
• If the test lamp does not illuminate, test the brake booster pump relay switch B+ circuit for a short to ground or an open/high resistance.
5. Verify that a test lamp illuminates between the brake booster pump relay coil B+ circuit terminal 85 and ground.
• If the test lamp does not illuminate, test the brake booster pump relay coil B+ circuit for a short to ground or an open/high resistance.
6. Disconnect the harness connector at the auxiliary brake booster pump.
7. Test for less than 10 ohms between the auxiliary brake booster pump ground circuit terminal 2 and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance.
8. Connect the harness connector at the auxiliary brake booster pump.
9. Connect a 20 A fused jumper wire between the brake booster pump relay switch B+ circuit terminal 30 and the auxiliary brake booster pump control circuit terminal 87. Verify the auxiliary brake booster pump is activated.
• If the auxiliary brake booster pump does not activate, test the auxiliary brake booster pump control circuit for an open/high resistance. If the circuit tests normal, test or replace the auxiliary brake booster pump.
10. Connect a test lamp between the brake booster pump relay coil B+ circuit terminal 85 and the brake booster pump relay control circuit terminal 86.
11. Command the auxiliary brake booster pump ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
• If the test lamp is always ON, test the brake booster pump relay control circuit for a short to ground. If the circuit tests normal, replace the electronic brake control module.
• If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the electronic brake control module.
12. If all circuits test normal, test or replace the brake booster pump relay.
Component Testing
Auxiliary Brake Booster Pump Test
1. Ignition OFF, disconnect the harness connector at the auxiliary brake booster pump.
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 auxiliary brake booster pump activates.
• If the auxiliary brake booster pump does not activate, replace the auxiliary brake booster pump.
Relay Test
1. Ignition OFF, disconnect the brake booster pump relay.
2. Test for 60-100 ohms between terminals 85 and 86 of the relay.
• If not within the specified range, replace the brake booster 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 brake booster 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 ohms between terminals 30 and 87.
• If greater than the specified value, replace the brake booster pump relay.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* Power Brake Booster Auxiliary Pump Replacement Service and Repair
* Relay Replacement (Within an Electrical Center) Relay Replacement (Within an Electrical Center)Relay Replacement (Attached to Wire Harness) Relay Replacement (Attached to Wire Harness)
* Control Module References Control Module References for EBCM replacement, setup, and programming