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 P0556: Brake Booster Pressure Sensor Performance
DTC P0557: Brake Booster Pressure Sensor Circuit Low Voltage
DTC P0558: Brake Booster Pressure Sensor Circuit High Voltage

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
5-Volt Reference | P0557 | P0557 | P0558 | P0556
Brake Booster Vacuum Sensor Signal | P0557 | P0557 | P0558 | P0556
Low Reference | -- | P0557 | -- | P0556

### Circuit/System Description

The brake booster pressure sensor measures the negative air pressure or vacuum reserve in the brake booster assembly. During engine running conditions, the brake booster pressure sensor signal circuit voltage varies, depending on the vacuum reserve internal to the brake booster.

### Conditions for Running the DTC

#### P0556

Engine running at idle.

#### P0557 or P0558

Ignition ON.

### Conditions for Setting the DTC

#### P0556

The ECM detects brake booster vacuum as being less than the intake manifold vacuum for more than 100 milliseconds.

#### P0557

The ECM detects less than 0.04 volts on the brake booster sensor signal circuit for more than 12.5 milliseconds.

#### P0558

The ECM detects greater than 4.89 volts on the brake booster sensor signal circuit for more than 12.5 milliseconds.

### Action Taken When the DTC Sets

DTCs P0556, P0557 or P0558 are Type B DTCs.

### Conditions for Clearing the DTC

DTCs P0556, P0557 or 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

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the brake booster vacuum sensor.
2. Ignition OFF, wait 60 seconds, test for less than 5 ohms between the low reference circuit terminal 2 and ground.

⇒ | If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

3. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal 1 and ground.

⇒ | If less than the specified range, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.

⇒ | If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the ECM.

4. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal 1 and the signal circuit terminal 3.

⇒ | If less than the specified range, test the signal circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

⇒ | If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.

5. Ignition OFF, disconnect the X2 harness connector at the ECM.
6. Ignition OFF, test for infinite resistance between the signal circuit terminal 29 and ground.

⇒ | If not the specified value, test the signal circuit for a short to ground.

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

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Power Brake Booster Vacuum Sensor Replacement

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