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 Descriptors

DTC C0550 00: EEPROM Checksum Mismatch
DTC C0550 39: EEPROM Checksum Mismatch

### Circuit/System Description

When the ignition is turned ON, the microprocessor runs a diagnostic program to detect an internal fault when power up is commanded. If an internal malfunction is detected, the control module will store a DTC C0550 in its memory.

### Conditions for Running the DTC

The microprocessor runs a diagnostic program to detect an internal fault when power up is commanded. The only requirements are voltage and ground.

### Conditions for Setting the DTC

• | The control module detects an internal write malfunction.

• | The control module detects an internal checksum malfunction.

### Action Taken When the DTC Sets

If equipped, the following module specific actions may occur:

• | The antilock brake system (ABS) indicator turns ON.

• | The BRAKE warning indicator turns ON.

• | The electronic brake control module (EBCM) disables the ABS/dynamic rear proportion (DRP)/traction control system (TCS).

• | The driver information center (DIC) displays the power steering warning message No Steering Assist.

• | The TCS indicator turns ON.

### Conditions for Clearing the DTC

• | A current DTC clears when the malfunction is no longer present.

• | A history DTC clears when the control module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

### Reference Information

#### Schematic Reference

Data Communication Schematics

#### Connector End View Reference

Data Communication Connector End Views

#### Description and Operation

Data Link Communications Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

• | Scan Tool Output Controls

• | Scan Tool Data List

• | Scan Tool Data Definitions

### Circuit/System Verification

Verify that DTC C0550 is not set.

⇒ | If the DTC is set, perform the learn procedure on the control module. If the DTC resets, replace the applicable control module.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for control module replacement, setup, and programming