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 U209A 00: High Speed Communication Enable Circuit Low

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Ignition Voltage (Circuit 2139)

P2534* **

P2534**

U209A** or B1453

--

Ignition Voltage (Circuit 239)

B1453* **

B1453**

U209A** or B1453

--

Communication Enable Signal (Circuit 5986)

U209A** or U2099

U209A**

--

--

Wake Up Signal (Circuit 5985)

U1814*

U1812*

U209A*

--

* Circuit fuse will open

** May set other module/DTCs.

Circuit/System Description

Modules connected to the high and low speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver module as an availability indication of the transmitter module. Each message contains the identification number of the transmitter module.

Wake up signal circuits are energized by the body control module (BCM) to activate the serial data gateway module (SDGM) and other modules, including the BECM, immediately when serial data is required. Additionally after receiving this signal the SDGM energizes another wake up signal to activate the drive motor generator battery control module (BECM) among others.

Conditions for Running the DTC

    • The system voltage is between 9-16 volts.
    • The ignition key is OFF.

Conditions for Setting the DTC

    • The communication enable signal circuit is open/high resistance.
    • The wake up signal circuit is shorted to voltage.

Action Taken When the DTC Sets

The MIL may illuminate and the DIC may display multiple messages.

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
    •  Control Module References

Connector End View Reference

Component Connector End Views

Description and Operation

Data Link Communications Description and Operation

Electrical Information Reference

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

Circuit/System Verification

With a scan tool, ensure the following DTCs are not present in the modules as follows:

BCM

    •  U1814
    •  U2099

SDGM

    •  U1812
    •  B1453

If any listed DTC is present, refer to Diagnostic Trouble Code (DTC) List - Vehicle to diagnose that DTC prior to this diagnostic.

Circuit/System Testing

  1. Ignition OFF, disconnect the harness connector X2 at the SDGM.
  2. Verify less than 0.5 volts between the wake up signal circuit terminal 19 and ground.
  3. If greater than the specified range, test the circuit for a short to voltage. If the circuit tests normal, replace the BCM.
  4. Ignition ON, verify B+ between the communication enable signal circuit terminal 16 and ground.
  5. If less than the specified value, test the circuit for an open/high resistance. If the circuit tests normal, replace the BCM.
  6. If all circuits test normal, replace the SDGM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

GMLAN Wiring Repairs