Symptom Related Diagnostic Procedures
Brake Booster Pump Motor Malfunction
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.
Circuit/System Description
The brake booster vacuum sensor measures the vacuum in the brake booster assembly. The engine 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 engine control module. When the vacuum within the system becomes weak, the engine control module turns ON the brake booster pump motor by providing ground to the brake booster pump motor relay. The relay activates and supplies battery voltage to the brake booster pump motor.
Reference Information
Schematic Reference
Hydraulic Brake Schematics [1][2]Electrical Diagrams
Connector End View Reference
Component Connector End Views Fuel Pump and Level Sensor Assembly - Primary
Description and Operation
Brake Booster Vacuum Assist Description and Operation Brake Booster Vacuum Assist
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 ON.
2. Verify that DTC P0556, P0557, P0558, or C027B is not set.
• If any listed DTC is set
Refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle.
• If the DTC is not set
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. 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 the inspection is OK
5. All OK.
Circuit/System Testing
1. Ignition OFF and all vehicle systems OFF, disconnect the 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. Connect a test lamp between the control circuit terminal 86 and B+, ignition ON.
3. 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 X1 at the K20 Engine Control Module.
2. Test for less than 1 V between the control circuit terminal 18 and ground.
• If 1 V or greater, repair the short to voltage on the circuit.
• If less than 1 V.
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 K20 Engine Control Module.
• If the test lamp is always ON
1. Ignition OFF, disconnect the harness connector X1 at the K20 Engine 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, replace the K20 Engine Control Module.
• If the test lamp turns ON and OFF
4. Ignition ON.
5. Verify that a test lamp illuminates between the B+ circuit terminals listed below and ground.
* Terminal 30
* Terminal 85
• 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 KR14 Brake Booster Pump Motor Relay.
• If the test lamp illuminates
6. Ignition OFF, connect the KR14 Brake Booster Pump Motor Relay, disconnect the G6 Brake Booster Pump - Auxiliary.
7. Test for less than 10 ohms between the ground circuit terminal 2 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
8. Connect a test lamp between the control circuit terminal 1 and ground, ignition ON.
9. 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 KR14 Brake Booster Pump Motor Relay.
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 KR14 Brake Booster Pump Motor Relay.
• If the test lamp is always ON
1. Ignition OFF, disconnect the harness connector at the KR14 Brake Booster Pump Motor Relay.
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 KR14 Brake Booster Pump Motor Relay.
• If the test lamp turns ON and OFF
10. Ignition OFF, disconnect the G6 Brake Booster Pump - Auxiliary, install a 30 A fused jumper wire between terminal 1 and B+. Install a jumper wire between terminal 2 and ground.
11. Verify the G6 Brake Booster Pump - Auxiliary activates.
• If the brake booster pump motor does not activate
Replace the G6 Brake Booster Pump - Auxiliary.
• If the brake booster pump motor activates
12. Replace the KR14 Brake Booster Pump Motor Relay.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the 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)
* Power Brake Booster Auxiliary Pump Replacement Service and Repair
* Control Module References Control Module References for Engine Control Module replacement, programming and setup.