GM Service Manual Online
For 1990-2009 cars only

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 U2136: No Exterior Mirror Communication

Circuit/System Description

The memory seat module (MSM) continuously sends a communication signal to the MCM. Upon receiving the signal, the MCM sends a reply signal, confirming that it can communicate.

Conditions for Running the DTC

The MSM is active.

Conditions for Setting the DTC

The MSM does not receive a response from the MCM for 10 or more consecutive seconds.

Action Taken When the DTC Sets

The memory recall function is disabled.

Conditions for Clearing the DTC

    • The current DTC will clear when the MSM receives a communication reply from the MCM.
    • The history DTC will clear after 50 fault-free ignition cycles have occurred.

Reference Information

Schematic Reference

    •  Driver Seat Schematics .
    •  Outside Rearview Mirror Schematics .

Connector End View Reference

Component Connector End Views

Electrical Information Reference

    •  Circuit Testing .
    •  Connector Repairs .
    •  Testing for Intermittent Conditions and Poor Connections .
    •  Wiring Repairs .

Scan Tool Reference

Control Module References

Circuit/System Testing

  1. Disconnect the A154 SIM connector, and the A21-X3 MSM connector.
  2. Using a DMM test the SIM; position 1, position 2, position 3, mirror dip, UART, module wake-up and power circuits for resistance.
  3. If greater than 5 ohms, repair or replace the effected circuit(s).
    If less than 5 ohms, replace the MSM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Memory Seat Control Module Replacement .