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

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 multi-function 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 multi-function switch.
2. Test for less than 10 ohm 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 circuit fuse is open, test the control circuits of the S56 radio control multi-function switch for a short to ground. If the circuits test normal, replace the S56 radio control multi-function switch.

4. Test for 2-10 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 P17 info display module.
• 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 P17 info display module.

5. If all circuits test normal, replace the S56 radio control multi-function switch.

Repair Instructions

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

* GMLAN Wiring Repairs (GMLAN Wiring Repairs)
* Control Module References (Programming and Relearning)for control module replacement, programming and setup