Vehicles Greater Than or Equal to 8600LB GVW

DTC C0055 or P0609 (Greater than or equal to 8600lb GVW)

Diagnostic Instructions
• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Diagnostic System Check - Vehicle
• Review Strategy Based Diagnosis for an overview of the diagnostic approach. Strategy Based Diagnosis
• Diagnostic Procedure Instructions provides an overview of each diagnostic category. Diagnostic Procedure Instructions

DTC Descriptors
DTC C0055 01: Rear Wheel Speed Sensor Circuit Short to Battery
DTC C0055 04: Rear Wheel Speed Sensor Circuit Open Circuit
DTC C0055 26: Rear Wheel Speed Sensor Circuit Frequency Too Low
DTC P0609: Vehicle Speed Output Circuit

Circuit/System Description
The vehicle speed sensor (VSS) also called the output speed sensor (OSS) creates a AC voltage signal that increases in frequency as vehicle speed increases. The transmission control module (TCM) receives and process this signal. The TCM provides a digital VSS signal on the data communication line to the engine control module (ECM) and other controllers connected to the data line. The electronic control module (ECM) converts the data from the vehicle speed sensor to a 128K pulses/mile signal. The electronic brake control module (EBCM) uses the vehicle speed signal from the ECM in order to calculate the rear wheel speed.

Conditions for Running the DTC
• The ignition is ON.
• Ignition voltage is greater than 10 volts.

Conditions for Setting the DTC
The EBCM detects a short to voltage, short to ground or an open/high resistance on the rear wheel speed sensor signal circuit.

Action Taken When the DTC Sets
• The EBCM disables the Antilock Brake System (ABS)/Traction Control System (TCS) for the duration of the ignition cycle.
• A driver information center message and/or a warning indicator may be displayed.

Conditions for Clearing the DTC
• The condition for setting the DTC is no longer present.
• The EBCM clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

Diagnostic Aids
• Visually inspect the vehicle speed sensor or output speed sensor for cracks or damage.
• Ensure the vehicle speed sensor or output speed sensor is properly torqued.
• Inspect the internal tone ring or gear teeth for damage.
• Check for missing pulses or electrical noise on the replicated transmission output speed signal.

Reference Information

Schematic Reference
Antilock Brake System Schematics Electrical Diagrams

Connector End View Reference
Antilock Brake System Connector End Views Connector Views

Description and Operation
ABS Description and Operation Description and Operation

Electrical Information Reference
• Circuit Testing Circuit Testing
• Connector Repairs Connector Repairs
• Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs Wiring Repairs

Scan Tool Reference
Scan tool information Scan Tool Testing and Procedures

Circuit/System Testing

Note: A condition may result in a stored history DTC C0055, check the replicated transmission output speed signal circuit for damaged wires, missing pulses or electrical noise that may be passed to 128 K pulses/mile engine speed signal.

1. Ignition OFF disconnect the harness connector at the EBCM.

2. Ignition ON, test for greater than 10 Volts between the signal circuit terminal 20 and ground.
--> If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.

3. Ignition OFF, disconnect the appropriate harness connector listed below at the ECM:
• X1 (Gas)
• X2 (Diesel)

4. Ignition ON, verify that a test lamp does not illuminate between the appropriate signal circuit terminal listed below and ground:
• Terminal 57 X1 (Gas)
• Terminal 54 X2 (Diesel)
--> If the test lamp illuminates, test the signal circuit for a short to voltage.

5. If the circuit tests normal, replace the EBCM.

Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure Verification Tests
EBCM replacement Service and Repair
ECM replacement Service and Repair
EBCM programming and setup Testing and Inspection
ECM programming and setup Programming and Relearning