P0556

DTC P0556, P0557, or P0558

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy 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 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.

P0557

The ECM detects open/high resistance, or short to ground on the brake booster sensor signal circuit.

P0558

The ECM detects short to voltage on the brake booster sensor signal circuit.

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 ([1][2]Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

Brake Assist System Description and Operation (Brake Assist System 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)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Diagnostic Trouble Code Descriptions)

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. 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 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 (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