P0556

DTC P0556, P0557, or P0558

Diagnostic Instructions

* Perform theDiagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* ReviewStrategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview)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/System Description

The power brake booster vacuum sensor monitors the vacuum pressure in the brake booster. The ECM compares the readings of the engine vacuum with the brake booster vacuum.


Conditions for Running the DTC


P0556
* Engine is running and vehicle speed is above 40 km/h (25 mph).
* No TPS sensor DTCs are present.
* The transmission is in drive.


P0557 or P0558

Engine running.


Conditions for Setting the DTC


P0556
* Engine is running.
* The ECM detects the vacuum level between the engine and brake booster is greater than 6kPa.


P0557

The ECM detects a short to ground or open in either the sensor signal circuit or the brake booster vacuum sensor.

P0558

The ECM detects an open with the sensor ground or a short to voltage in either the signal circuit or the brake booster vacuum sensor.


Action Taken When the DTC Sets

* MIL is illuminated after two fault trips.
* ABS warning indicator is illuminated.



Conditions for Clearing the DTC

The conditions for the DTC are no longer present.


Reference Information
Schematic Reference

Hydraulic Brake Schematics (Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

Hill Hold Control Description and Operation (Hill Hold Control Description and Operation)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning)for scan tool information


Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the brake booster vacuum sensor.
2. Ignition OFF, 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. Verify the scan tool ECM Brake Booster Pressure Sensor parameter is less than 0.15 volt.

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

5. Install a 3A fused jumper wire between the signal circuit terminal 3 and the 5-volt reference circuit terminal 1. Verify the scan tool ECM Brake Booster Pressure Sensor parameter is greater than 4.75 volts.

• If less than the specified range, test the signal circuit for short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.

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



Repair Instructions

Perform theDiagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Power Brake Booster Vacuum Sensor Replacement (Service and Repair)
* Control Module References (Programming and Relearning)for ECM replacement, setup, and programming