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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2008 🢒 Acadia - AWD 🢒 Diagnostic Navigation 🢒 Vehicle Diagnostic Information 🢒 Scan Tool Does Not Communicate with Low Speed GMLAN Device

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.

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Low Speed GMLAN Serial Data

1

2*

1

--

Ground (DLC, Terminal 5)

--

1*

--

--

* An open between the data link connector (DLC) and JX 205, or DLC terminal 5 ground will only effect the communication with the scan tool. See Diagnostic Aids.

1. No communication on any low speed GMLAN module.

2. No communication on a specific low speed GMLAN module, or group of modules.

Circuit/System Description

Modules connected to the low speed GMLAN serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules when the ignition switch is in any position other than OFF. The low speed GMLAN serial data circuit uses JX 205 and JX 405 as common connection points between some modules and the data link connector (DLC).

Diagnostic Aids
    • Use the Data Link References to identify the low speed GMLAN serial data modules.
    •  This test is used for a total low speed GMLAN communication failure. If only one module is not communicating and sets no DTC, ensure that the vehicle is equipped with the module, then use DTC U0100-U0299 for diagnostics.
    • An open in the low speed GMLAN serial data circuit between the splice pack and a module will only effect the specific module. This type of failure will set a loss of communication DTC for each module effected, and the other modules will still communicate.
    • An open in the DLC ground circuit terminal 5 will allow the scan tool to operate to set up the vehicle on the tool and then not communicate with the vehicle. When the scan tool is to the point of communicating with the vehicle, a message on the scan tool will indicate "no CANdi module detected" and will not communicate.
    • An open between the DLC and JX 205 will only effect the communication with the scan tool. The vehicle modules will still communicate, and the vehicle will start.
    • The engine will not start when there is a total malfunction of the low speed GMLAN serial data circuit.
        The following conditions may cause a total loss of low speed GMLAN data communication:
       - The low speed GMLAN serial data circuit shorted to ground or voltage.
       - A module internal malfunction that causes a short to voltage or ground on the low speed GMLAN circuit.

Reference Information

Schematic Reference

Data Communication Schematics

Connector End View Reference

    •  Component Connector End Views
    •  Splice Pack Connector End Views

Description and Operation

Data Link Communications Description and Operation

Electrical Information Reference

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

Circuit/System Testing
  1. Test for less than 1.0 ohm between the ground circuit terminal 5 of the DLC and ground.
    2. ⇒If greater than the specified range, test the ground circuit for open/high resistance.
  2. Ignition OFF, disconnect the harness connector at JX 205.
  3. Ignition ON, test for less than 1 volt between the serial data circuit terminal 1 of the DLC and ground.
    4. ⇒If greater than the specified range, test the serial data circuit for a short to voltage.
  4. Test for infinite resistance between the serial data circuit terminal 1 of the DLC and ground.
    5. ⇒If less than the specified value, test the serial data circuit for a short to ground.
  5. Test for less than 2 ohms on the serial data circuit between terminal 1 of the DLC and terminal 1 of JX 205.
    6. ⇒If greater that the specified range, test the serial data circuit for an open/high resistance.
  6. Install a 3A fused jumper wire between terminal 1 and terminal 2 of JX 205. Attempt to communicate with the remote control door lock receiver (RCDLR). Communication should be available.
    7. ⇒If communication is not available refer to JX 405 Circuit Test.
  7. Install another 3-amp fused jumper wire to terminal 1 of JX 205.

    8. Important: Allow communications for 5 seconds after connecting a module with the jumper to determine if communication is interrupted or not.

  8. With RCDLR communications established, use the other end of the jumper wire to connect all other terminals of JX 205, harness side, one at a time and verify that low speed communication remains available to the RCDLR.
    9. ⇒If communication is interrupted after connecting an individual module at JX 205, test the serial data circuit between JX 205 and the last module connected for a short to voltage or short to ground. If the circuit tests normal, replace the module that caused no communication.

JX 405 Circuit Test
  1. Ignition OFF, remove the scan tool from the DLC, and disconnect the harness connector at JX 405.
  2. Ignition ON, test for less than 1 volt between serial data circuit terminal 1 of JX 405 and ground.
    3. ⇒If greater than the specified range, test the serial data circuit for a short to voltage.
  3. Test for infinite resistance between the serial data circuit terminal 1 of JX 405 and ground.
    4. ⇒If less than the specified value, test the serial data circuit for a short to ground.
  4. Disconnect the fused jumper from JX 205 terminal 2, and connect to terminal 12. Install another 3-amp fused jumper wire to terminal 1 of JX 205.
  5. Establish communications with the BCM.

    6. Important: Allow communications for 5 seconds after connecting a module with the jumper to determine if communication is interrupted or not.

  6. With BCM communications established, use the other end of the jumper wire to connect the JX 405 terminals listed, one at a time and verify that low speed communication remains available to the BCM.
    7. • 4 - RPO UK8
    • 6
    • 7 - RPO UD7
    • 8 - RPO UE1
    • 9 - RPO U2K
    • 11 - RPO E61
    • 12 - RPO A45 or KA1
    ⇒If communication is interrupted after connecting an individual module at JX 405, test the serial data circuit between JX 405 and the last module connected for a short to voltage or short to ground. If the circuit tests normal, replace the module that caused no communication.
  7. Disconnect the harness connector at the rollover sensor.
  8. Connect the open end of the fused jumper wire to the serial data circuit terminal 10 of JX 405 and attempt to communicate with the BCM. Communication should not be available.
    9. ⇒If communication is available, replace the rollover sensor.
  9. Ignition OFF, disconnect the harness connector at the passenger presence system (PPS) module, and attempt to communicate with the BCM. Communication should not be available.
    10. ⇒If communication is available, test the serial data circuit between the PPS and the rollover sensor for a short to voltage or short to ground. If the circuit tests normal, replace the PPS module.
  10. Ignition OFF, disconnect the harness connector at the inflatable restraint sensing and diagnostic module (SDM), and attempt to communicate with the BCM. Communication should not be available.
    11. ⇒If communication is available, test the serial data circuit between the SDM and the PPS module for a short to voltage or short to ground. If the circuit tests normal, replace the SDM.
  11. Test the serial data circuit between the SDM and the PPS module for a short to voltage or short to ground.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

    •  GMLAN Wiring Repairs
    •  Control Module References for module replacement, setup, and programming