For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Review Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptor

DTC P0555 04: Brake Booster Pressure Sensor Circuit Open
DTC P0555 02: Brake Booster Pressure Sensor Circuit Short to Ground
DTC P0558 01: Brake Booster Pressure Sensor Circuit High Voltage

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Relay Coil B+ | P0555 02 | P0555 04 | -- | --
Relay Coil Control | 1 | 1 | P0558 01 | --
Brake Booster Pump Control | 1 | 1 | 1 | --
Brake Booster Pump Ground | 1 | 1 | -- | --
1. Brake Booster Pump Malfunction

### Circuit/System Description

The ECM commands the vacuum pump relay ON to activate the power brake booster vacuum pump to maintain the vacuum needed when the brakes are applied.

### Conditions for Running the DTC

Ignition ON

### Conditions for Setting the DTC

The ECM detects a short to voltage, short to ground or an open/high resistance on the relay coil circuit.

### Action Taken When the DTC Sets

DTC P0555 and P0558 are Type B DTCs.

### Conditions for Clearing the MIL/DTC

DTC P0555 and P0558 are Type B DTCs.

### Reference Information

#### Schematic Reference

Hydraulic Brake Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Brake Assist System Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Testing

1. Ignition OFF, disconnect the K8 vacuum 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 86 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 ignition circuit fuse is open, test or replace the relay.

4. 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.

5. Verify that a test lamp does not illuminate between the control circuit terminal 85 and ground.

⇒ | If the test lamp illuminates, test the control circuit for a short to voltage.

6. Disconnect the harness connector at the vacuum pump.
7. Test for less than 2 ohms between the vacuum 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 vacuum pump.
9. Connect a 20A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the vacuum pump is activated.

⇒ | If the vacuum pump does not activate, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the power vacuum brake booster.

10. Ignition OFF, test for infinite resistance between the control circuit terminal 85 and ground.

⇒ | If less than the specified value, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM

11. Disconnect the X2 harness connector at the ECM.
12. Test for less than 2 ohms between the control circuit terminal 85 at the pump relay cavity and terminal 48 at the ECM harness connector.

⇒ | If greater than the specified range, test the control circuit for an open/high resistance.

13. If all circuits test normal, test or replace the power vacuum brake booster.

### Component Testing

1. Ignition OFF, disconnect the relay.
2. Test for 60-180 ohms between terminals 85 and 86.

⇒ | If the resistance is not within the specified range, replace the relay.

3. Test for infinite resistance between the following terminals:

• | 30 and 86

• | 30 and 87

• | 30 and 85

• | 85 and 87

⇒ | If not the specified value, replace the relay.

4. Install a 30A fused jumper wire between relay terminal 85 and B+. Install a jumper wire between relay terminal 86 and ground.
5. Test for less than 2 ohms between terminals 30 and 87.

⇒ | If greater than the specified range, replace the relay.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Relay Replacement

• | Power Vacuum Brake Booster Replacement

• | Control Module References for ECM replacement, setup, and programming