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

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Lost Communication With Front Controls Multifunction Interface Module

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 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

* A supervised periodic message that includes the transmitter module availability has not been received.

* 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 Connector End Views By Name

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 Programming and Relearning for scan tool information

Circuit/System Testing

Note:

* Use the schematic to identify the following:

- Control module and LIN device locations on the serial data circuit.

- The control module serial data circuit terminals and the LIN device B+, ignition, 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 ground circuit and ground.

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

3. Ignition ON, verify that a test lamp illuminates between B+ circuit and ground.

• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuits test normal, replace the S56 radio control multifunction switch.

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

• If greater than the specified range, test the serial data circuit for a short to voltage. If the circuit tests normal, replace the A22 radio controls.

• If less than the specified range, test the serial data circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the A22 radio controls.

5. If all circuits test normal, replace the S56 radio control multifunction switch.

Repair Instructions

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

* GMLAN Wiring Repairs GMLAN Wiring Repairs

* Audio Multifunction Control Replacement Audio Multifunction Control Replacement

* Radio Control Module Replacement Radio Control Module Replacement

* Control Module References Programming and Relearning for control module replacement, programming and setup