Radio Controls Malfunction (with Monochrome Display)

Radio Controls Malfunction (with Monochrome Display)

Diagnostic Instructions

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

Circuit/System Description

The radio/HVAC controls are supplied battery voltage and ground. The radio/HVAC controls operate radio functions through serial data messages. The radio/HVAC controls communicate control requests to the info display module through LIN serial data. The info display module communicates these control requests to the radio through CGI serial data.

Communications between the HVAC controls and the HVAC control module are on a separate LIN circuit. The HVAC control module communicates status information to the radio via GMLAN for HVAC information display.

Reference Information
Schematic Reference

Radio/Navigation System Schematics Radio/Navigation System Schematics
Connector End View Reference

Component Connector End Views Connector End Views By Name
Description and Operation

Radio/Audio System Description and Operation Radio/Audio System
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

Control Module References Control Module Referencesfor scan tool information

Circuit/System Verification

1. Verify no DTCs are set as current.

• If any DTCs are set as current, refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle.

2. Ignition ON, radio ON, verify the radio/HVAC controls backlighting illuminates and that all controls perform the correct function.

• If some, but not all, controls operate normally, replace the radio/HVAC control.
• If all controls are inoperative, refer to Circuit/System Testing.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the A20 radio/HVAC controls.
2. Test for less than 10 ohm between the ground circuit terminal 17 and ground.

• If greater than the specified range, test the ground circuit for an open/high resistance.

3. Verify that a test lamp illuminates between the B+ circuit terminal 10 and ground.

• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

4. Ignition ON, test for 2-11.5 V between the data circuit terminal 7 and ground.

• If less than the specified range, test the data circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the P17 info display module.
• If greater than the specified range, test the data circuit for a short to voltage. If the circuit tests normal, replace the P17 info display module.

5. If all circuits test normal, replace the A20 radio/HVAC controls.

Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.

* Heater and Air Conditioning and Radio Control Module Replacement Service and Repair
* Driver Information Display Replacement Service and Repair
* Control Module References Control Module Referencesfor radio replacement, setup, and programming