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 Descriptor

DTC P0557: Brake Booster Pressure Sensor Circuit Low Voltage

### Diagnostic Fault Information

Circuit | Short to Ground | High Resistance | Open | Short to Voltage | Signal Performance
--- | --- | --- | --- | --- | ---
5-Volt Reference | P0557 | P0557 | P0557 | -- | --
Brake Boost Pressure Sensor Signal | P0557 | P0557 | P557 | P0558 | P0556
Low Reference | -- | P0558 | P0558 | -- | --

### Circuit Description

The brake booster pressure sensor measures the negative air pressure or vacuum in the brake booster assembly. The engine control module (ECM) supplies the following circuits to the brake booster pressure sensor:

• | A 5-volt reference circuit

• | A signal circuit

• | A low reference circuit

During engine running conditions, the brake booster pressure sensor signal circuit voltage varies, depending on the vacuum reserve internal to the brake booster. If the ECM detects that the brake booster vacuum is at a low voltage, then DTC P0557 sets.

### Conditions for Running the DTC

• | The engine is running at an idle condition.

• | The ignition voltage is greater than 11 volts, but less than 18 volts.

• | DTC P0557 runs continuously once the above conditions are met.

### Conditions for Setting the DTC

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

### Action Taken When the DTC Sets

• | The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.

• | The control module records the operating conditions at the time the diagnostic fails. The control module stores the information in the Freeze Frame/Failure Records.

### Conditions for Clearing the MIL/DTC

• | The control module turns OFF the MIL after 3 consecutive ignition cycles that the diagnostic runs and does not fail.

• | A current DTC, last test failed, clears when the diagnostic runs and passes.

• | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

• | Clear the MIL and the DTC with a scan tool.

### Reference Information

#### Schematic Reference

Hydraulic Brake Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Brake Warning 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 Verification

Important: Verify that the engine is in good mechanical condition before continuing with this diagnostic.

• | Verify the integrity of the entire air induction system by inspecting for the following conditions:

- | An air flow restriction

- | Any vacuum leak

- | Improper routing or connecting of any vacuum hoses, including those on the turbocharger bypass valve solenoid and the turbocharger wastegate solenoid

- | In cold climates, inspect for any snow or ice buildup

• | Verify with a scan tool that all parameters are with in the proper range.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the brake boost pressure sensor.
2. Ignition OFF for 90 seconds, test for less than 5 ohms of resistance 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. Verify the scan tool Brake Booster Pressure Sensor parameter is greater than 275 kPa.

⇒ | If less than the specified range, test the signal circuit terminal 3 for a short to ground. If the circuit tests normal, replace the ECM.

5. Install a 3A fused jumper wire between the signal circuit terminal 3 and the low reference circuit terminal 2. Verify the scan tool Brake Booster Pressure Sensor parameter is less than 1 kPa.

⇒ | If greater than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.

6. If the circuits test normal, replace the brake booster pressure sensor.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Power Brake Booster Vacuum Sensor Replacement

• | Control Module References for EBCM