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 Views
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. Ignition OFF, disconnect the harness at the brake booster pump relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.
• If the test lamp illuminates, test the control circuit for a short to voltage.
3. Verify that a test lamp illuminates between the B+ circuit terminal 30 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 and the B+, circuit fuse is open, test or replace the brake booster pump relay.
4. Verify that a test lamp illuminates between the Ignition, circuit terminal 86 and ground.
• If the test lamp does not illuminate, test the ignition, circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition, circuit fuse is open, test the control circuit terminal 87 for a short to ground.
5. Disconnect the harness connector at the brake booster pump.
6. Test for less than 1 ohm between the brake booster pump ground circuit terminal 2 and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance.
7. Connect the harness connector at the brake booster pump.
8. Connect a 20 A fused jumper wire between the B+, circuit terminal 30 and the control circuit terminal 87. Verify the brake booster pump is activated.
• If the brake booster pump does not activate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the brake booster pump.
9. Connect a test lamp between the ignition circuit terminal 86 and the control circuit terminal 85.
10. Command the 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 control circuit for a short to ground. If the circuit tests normal, replace the brake booster pump.
• 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 brake booster pump.
11. If all circuits test normal, test or replace the brake booster pump relay.
Component Testing
Vacuum Pump Motor Test
1. Ignition OFF, disconnect the harness connector at the M9 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 M9 brake booster pump activates.
• If the M9 brake booster pump does not activate, replace the M9 brake booster pump motor.
Relay Test
1. Ignition OFF, disconnect the brake booster pump relay.
2. Test for 60-100 ohm 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 ohm 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.
* Relay Replacement (Attached to Wire Harness) Relay Replacement (Attached to Wire Harness)Relay Replacement (Within an Electrical Center) Relay Replacement (Within an Electrical Center)
* Control Module References Control Module References for EBCM replacement, setup, and programming