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 Descriptor

DTC B1020 00: Auxiliary Electronic Control Unit (ECU) Performance

### Circuit/System Description

The navigation radio communicates with the radio display assembly via serial data. If the radio receives an improper status response message, DTC B1020 will set.

This DTC indicates an fault in the display. No external circuits are involved.

### Conditions for Running the DTC

• | Ignition is ON or in the ACC position.

• | The system voltage is at least 9.5 volts and no more than 15.5 volts.

• | All the above conditions are present for greater than 10 seconds.

### Conditions for Setting the DTC

The radio receives an improper status response indicating an internal ECU fault or a stuck button in the radio display assembly.

### Action Taken when the DTC Sets

No action is taken.

### Conditions for Clearing the DTC

• | A current DTC clears when the radio receives a proper status response message back from the radio control assembly.

• | A history DTC clears after 50 malfunction-free ignition cycles.

### Reference Information

#### Schematic Reference

Radio/Navigation System Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Radio/Audio System Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

Verify that DTC B1020 is not set.

⇒ | If the DTC is set, replace the radio display.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.