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 Descriptors
DTC C027B 00
- Brake Booster Electric Vacuum Pump
Diagnostic Fault Information
Circuit/System Description
The brake booster vacuum sensor measures the vacuum in the brake booster assembly. The electronic brake control module 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 electronic brake control module. When the vacuum within the system becomes weak, the electronic brake control module turns ON the brake booster pump motor by providing battery voltage to the brake booster pump motor relay. The relay activates and supplies ground to the brake booster pump motor.
Conditions for Running the DTC
Ignition ON.
Conditions for Setting the DTC
A short to ground, short to voltage or open/high resistance is detected on the control circuit.
Conditions for Clearing the DTC
The condition for setting the DTC is no longer present.
Reference Information
Schematic Reference
Hydraulic Brake Schematics [1][2]Electrical Diagrams
Connector End View Reference
Component Connector End Views Outside Rearview Mirror - Driver
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. Verify that the brake booster vacuum system has no damage, leakage or incorrect installation.
• If damage, leakage or incorrect installation is found
Refer to Brake Assist System Diagnosis Component Tests and General Diagnostics
• If no damage, leakage or incorrect installation is found
2. Ignition ON.
3. Verify the brake booster pump motor turns ON and OFF when commanding the brake booster electric vacuum pump ON and OFF with a scan tool.
• If the brake booster pump motor does not turn ON and OFF
Refer to Circuit/System Testing.
• If the brake booster pump motor turn ON and OFF
4. All OK.
Circuit/System Testing
1. Ignition OFF and all vehicle systems OFF, disconnect the X1 harness connector at the KR14 Brake Booster Pump Motor Relay. It may take up to 2 minutes for all vehicle systems to power down.
2. Test for less than 10 ohms between the ground circuit terminal 1 and ground.
• If 10 ohms or greater
1. Test for less than 2 ohms in the ground circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, repair the open/high resistance in the ground connection.
• If less than 10 ohms
3. Ignition ON.
4. Verify that a test lamp illuminates between the B+ circuit terminal 5 and ground.
• If the test lamp does not illuminate and the circuit fuse is good
1. Ignition OFF.
2. Test for less than 2 ohms in the B+ circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse.
• If the test lamp does not illuminate and the circuit fuse is open
1. Ignition OFF.
2. Test for infinite resistance between the B+ circuit and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance, replace the M9 Brake Booster Pump Motor.
• If the test lamp illuminates
5. Connect a test lamp between the control circuit terminal 2 and ground.
6. Verify the test lamp turns ON and OFF when commanding the brake booster electric vacuum pump ON and OFF with a scan tool.
• If the test lamp is always OFF
1. Ignition OFF, disconnect the harness connector at the K17 Electronic Brake Control Module.
2. Test for infinite resistance between the control circuit and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance
3. Test for less than 2 ohms in the control circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, replace the K17 Electronic Brake Control Module.
• If the test lamp is always ON
1. Ignition OFF, disconnect the harness connector at the K17 Electronic Brake Control Module, ignition ON.
2. Test for less than 1 V between the control circuit and ground.
• If 1 V or greater, repair the short to voltage on the circuit.
• If less than 1 V, replace the K17 Electronic Brake Control Module.
• If the test lamp turns ON and OFF
7. Replace the KR14 Brake Booster Pump Motor Relay.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the repair.
* Power Brake Booster Pump Replacement Service and Repair
* Control Module References Control Module References for Electronic Brake Control Module replacement, programming and setup.