U1901

DTC U1901

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 Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC U1901 00
- Lost Communication With Front Controls Multifunction Interface Module Malfunction

Diagnostic Fault Information






Circuit/System Description

The Radio interfaces only with the Info Display Module and the Info Display Module communicates with the Radio/HVAC Control through a Linear Interconnect Network (LIN) interface. The Info Display Module is responsible for passing information between the Radio and the Radio/HVAC Control.

Conditions for Running the DTC

* The system voltage is between 9-16 V.

* The vehicle power mode master requires serial data communication to occur.

Conditions for Setting the DTC

Radio detects an invalid signal from S56 Radio Control Multifunction Switch.

Action Taken When the DTC Sets

Radio menu navigation and control will not function with the multifunction controller.

Conditions for Clearing the DTC

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

* A history DTC clears when the module ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

Reference Information

Schematic Reference

* Data Communication Schematics [1][2]Electrical Diagrams

* Radio/Navigation System Schematics Radio/Navigation System Schematics

Connector End View Reference

Component Connector End Views Sunshade - Left

Description and Operation

* Data Link Communications Description and Operation 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 References for scan tool information

Circuit/System Testing

Note:

* Terminal and connector identifiers will be different depending on the individual device being tested. Use Schematic Reference and Connector End View Reference to identify device's connector, B+, ground, and serial data circuit terminals.

* A loss of serial data communications DTC does not represent a failure of the master control module that set it.

1. Ignition OFF, disconnect the harness connector at the S56 Radio Control Multifunction Switch.

2. Test for less than 10 ohms between the ground circuit terminal and ground.

• If 10 ohms or greater

1. Ignition OFF.

2. Test for less than 2 ohms in the ground circuit end to end.

• If 2 ohms or greater, repair the open/high resistance in the circuit.

• If less than 2 ohms, repair the open/high resistance in the ground connection.

• If less than 10 ohms

3. Ignition ON.

4. Verify a test lamp illuminates between the B+ circuit terminal and ground.

• If the test lamp does not illuminate and the circuit fuse is good

1. Ignition OFF.

2. Test for less than 2 ohms in the B+ circuit end to end.

• If 2 ohms or greater, repair the open/high resistance in the circuit.

• If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse.

• If the test lamp does not illuminate and the circuit fuse is open

1. Ignition OFF.

2. Test for infinite resistance between the B+ circuit terminal and ground.

• If less than infinite resistance, repair the short to ground on the circuit.

• If infinite resistance, replace the S56 Radio Control Multifunction Switch.

• If the test lamp illuminates

5. Ignition ON.

6. Test for 2-12 V between the serial data circuit terminal and ground.

• If less than 2 V

1. Ignition OFF, disconnect the harness connector at the A22 Radio Controls.

2. Test for infinite resistance between the serial data circuit terminal and ground.

• If less than infinite resistance, repair the short to ground on the circuit.

• If infinite resistance

3. Test for less than 2 ohms in the serial data circuit end to end.

• If 2 ohms or greater, repair the open/high resistance in the circuit.

• If less than 2 ohms

4. Replace the A22 Radio Controls.

• If greater than 12 V

1. Ignition OFF, disconnect the harness connector at the A22 Radio Controls.

2. Ignition ON.

3. Test for less than 1 V between the serial data circuit terminal and ground.

• If 1 V or greater, repair the short to voltage on the circuit.

• If less than 1 V

4. Replace the A22 Radio Controls.

• If between 2-12 V

7. Replace the S56 Radio Control Multifunction Switch.

Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests after completing the repair.

* GMLAN and Media Oriented Systems Transport (MOST) Wiring Repairs Service and Repair

* Audio Multifunction Control Replacement Audio Multifunction Control Replacement

* Radio Control Module Replacement Radio Control Module Replacement

* Control Module References Control Module References for device replacement, programming and setup