• 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.

For symptom byte information, refer to Symptom Byte List.

The internal fault detection is handled inside the device. The symptom byte information is for engineering reference only. No external circuit diagnosis is involved.

The device runs the program to detect an internal fault when power up is commanded. The only requirements are voltage and ground. This program runs even if the voltage is out of the valid operating range.

The device has detected an internal malfunction.

The device refuses all additional inputs.

• A current DTC clears when the malfunction is no longer present.
• A history DTC clears when the device ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

• This DTC may be stored as a history DTC without affecting the operation of the device.
• If stored only as a history DTC and not retrieved as a current DTC, do not replace the device.
• If this DTC is retrieved as both a current and history DTC, replace the device that set the DTC.

• Data Communication Schematics
• Control Module References

Master Electrical Component List

Data Link Communications Description and Operation

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

Control Module References for scan tool information

1. Ignition ON/Vehicle In Service Mode.
2. Verify DTC C056D is not set.
• If DTC C056D is set

  Replace the device that sets the DTC.

• If DTC C056D is not set
3. All OK

Perform the Diagnostic Repair Verification after completing the repair.

Control Module References for device replacement, programming and setup