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.

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

### DTC Descriptors

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 | High Resistance | Open | Short to Voltage | Signal Performance
--- | --- | --- | --- | --- | ---
Vacuum Assist Pump Relay Coil Control Circuit | P258C | P258C | P258C | P258D | P258B
Vacuum Pump Relay Switch Circuit | P258A | P258A | P258A | -- | P258B

### Circuit/System Description

The engine control module (ECM) grounds the vacuum pump relay, which is relay 38 control circuit through an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. Each driver has a fault line that is monitored by the ECM. When the ECM is commanding a component ON, the voltage potential of the control circuit should be low, near 0 volts. When the ECM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be high, near battery voltage. If the ECM detects that the actual state of the control circuit does not match the expected state, a DTC will set.

### Reference Information

#### Schematic Reference

Hydraulic Brake Schematics

#### Connector End View Reference

• | Hydraulic Brake Connector End Views

• | Engine Control Module Connector End Views

• | Engine Controls Connector End Views

#### Description and Operation

Cooling Fan 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

• | Scan Tool Data List

• | Scan Tool Data Definitions

• | Scan Tool Output Controls

### Circuit/System Verification

Important: If DTC P258B is set as current DTC, test for a vacuum leaks in the brake booster system. Refer to Brake System Vacuum Source Test .

1. If DTCs C0161 are set, perform those diagnostics first.
2. Ignition ON, command the relay ON and OFF with a scan tool. Observe to verify that the vacuum relay and motor turns ON and OFF with each command.

### Circuit/System Testing

Important: You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.

1. Ignition OFF, disconnect the relay.
2. Ignition OFF, connect a 20A fused jumper between the positive terminal at the battery, and the vacuum relay control voltage supply circuit terminal F8, and verify vacuum pump motor activation.

⇒ | If the vacuum pump motor does not activate, test the vacuum pump motor voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal, test the vacuum pump motor ground circuit for an open/high resistance. If the vacuum pump motor does not activate, and the circuits test normal, replace the vacuum pump motor.

3. Ignition ON, connect a 20A fused jumper from the relay ignition switch voltage supply circuit terminal, and the vacuum relay control voltage supply circuit terminal F8 , and verify vacuum pump motor activation.

⇒ | If the vacuum pump motor does not activate, test the relay ignition switch voltage supply circuit for a short to ground or an open/high resistance.

⇒ | If the circuit tests normal, test the ECM relay control circuit from the relay terminal D11 to the ECM for a an open/high resistance, or short to battery positive, repair as necessary.

4. If the vacuum pump motor and all circuits test normal, replace the faulty relay.
5. If the vacuum pump motor the relay, and all circuits test normal, replace the ECM.

### Repair Instructions

Cooling Fan and Shroud Replacement

### Repair Verification

Ignition ON, command the relay ON and OFF with a scan tool. Observe to verify that the vacuum pump control relay, and motor turns ON and OFF with each command.