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 P258A: Vacuum Pump Relay Control Circuit
DTC P258B: Vacuum Pump Performance
DTC P258C: Vacuum Pump Relay Control Circuit Low Voltage
DTC P258D: Vacuum Pump Relay Control Circuit High Voltage

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Relay Coil B+ | P258A | P258A, P258C | -- | P258B
Relay Coil Control | P258C | P258A | P258D | P258B
Brake Booster Pump Control | 1 | 1 | 1 | --
Brake Booster Pump Ground | 1 | 1 | -- | --
1. Brake Booster Pump Malfunction

### Circuit/System Description

The power brake booster vacuum sensor monitors the vacuum level in the brake booster. When the ECM detects the level has dropped too low, it 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

#### P258A, P258C, P258D

Ignition ON.

#### P258B

• | Engine Running

• | Vacuum pump is activated for greater than 1.6 seconds.

### Conditions for Setting the DTC

#### P258A, P258C

The ECM detects an open/high resistance on the relay coil control circuit.

#### P258B

The ECM detects an excessive difference in vacuum levels between the power brake booster and the manifold absolute pressure (MAP).

#### P258D

The ECM detects a short to voltage on the relay control circuit.

### Action Taken When the DTC Sets

DTC P258A, P258B, P258C, P258D are Type B DTCs.

### Conditions for Clearing the MIL/DTC

DTC P258A, P258B, P258C, P258D 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

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

Verify that a vacuum leak is not present, refer to Brake Assist System Diagnosis

### Circuit/System Testing

1. Ignition OFF, disconnect the 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 30 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 or replace the relay.

4. Verify that a test lamp illuminates between the ignition circuit terminal 85 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 the control circuit terminal 85 for a short to ground.

5. Verify that a test lamp does not illuminate between the control circuit terminal 86 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 ground or an open/high resistance. If the circuit tests normal, test or replace the vacuum pump.

10. Ignition OFF, test for infinite resistance between the control circuit terminal 86 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 86 at the relay cavity and terminal 20 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 brake booster vacuum pump.

### Component Testing

1. Ignition OFF, disconnect the vacuum pump 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 Brake Booster Auxiliary Pump Replacement

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