GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2009 🢒 Captiva Sport 🢒 Power and Signal Distribution 🢒 Data Communications 🢒 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 X 200, or DLC ground terminal 5 will only effect the communication with the scan tool. The vehicle modules will still communicate.

1. No communication on any low speed GMLAN module

2. No communication on a specific low speed GMLAN module

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 must be operational for the vehicle to start so the theft deterrent module (TDM) and body control module (BCM) can communicate. The low speed GMLAN serial data circuit uses JX 200 and JX 209 (splice pack combs) as a common connection between some modules and the 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 the 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. The vehicle modules will still communicate, and the vehicle will start.
    • An open between the DLC and JX 200 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
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Attempt to communicate with all modules on the low speed GMLAN bus.

⇒If any low speed module communicates and any DTC beginning with a U exists, refer to Diagnostic Trouble Code (DTC) List - Vehicle for diagnostics.

Circuit/System Testing

Low Speed GMLAN Initial Test

  1. Test for less than 1.0 ohm between the DLC ground circuit terminal 5 and ground.
    2. ⇒If greater than the specified range, test the ground circuit for open/high resistance.
  2. Ignition OFF, disconnect the harness connector (splice pack comb) at JX209.
  3. Ignition ON, with a scan tool, attempt to communicate with the BCM.
    4. ⇒If communication is available, refer to Diagnostic 2.
    ⇒If communication is not available refer to Diagnostic 1.

Diagnostic 1

  1. Ignition OFF, disconnect the harness connector (splice pack comb) at JX200.
  2. Ignition OFF, disconnect the harness connector at the inflatable restraint passenger presence system (PPS) sensor.
  3. Ignition ON, with a scan tool, attempt to communicate with the BCM. Communication should be available.
    4. ⇒If no communication, test the serial data circuit between the DLC, BCM, and the PPS sensor for a short to ground and short to voltage. If the circuit tests normal, replace the BCM.
  4. Ignition OFF, connect the harness connector at the PPS sensor.
  5. Ignition ON, attempt to communicate with the BCM. Communication should be available.
    6. ⇒If no communication, replace the PPS sensor.
  6. Ignition OFF, install a 3-amp fused jumper wire to terminal H of JX200 harness side and terminal G.
  7. Ignition ON, attempt to communicate with the IPC. Communications should be available.
    8. ⇒If communication is not available, test the serial data circuit between the splice pack terminal H and the IPC for a short to ground or a short to voltage. If the circuit tests normal, replace the IPC.

    Important: After each connection, cycle the ignition key off for 5 seconds, then ON before attempting to establish communication.

  8. Ignition OFF, with the jumper wire still attached to terminal H, individually move the other end of the jumper wire to each of the terminals listed below and attempt to communicate with the applicable module. Communications should be available with each module listed.
    9. • Terminal J, radio
    • Terminal E, TDM
    • Terminal C, HVAC control module
    • Terminal D, remote control door lock receiver (RCDLR)
    ⇒If any module does not communicate, test the serial data circuit between the applicable module harness connector and the JX200 splice pack connector for a short to ground or a short to voltage. If the circuit tests normal, replace the applicable module.

Diagnostic 2

  1. Ignition OFF, disconnect the harness connector (splice pack comb) at JX200.
  2. Ignition OFF, install a 3-amp fused jumper wire to terminal H of JX200 harness side and terminal C of JX209 splice pack harness side.
  3. Ignition ON, attempt to communicate with the inflatable restraint vehicle roll over sensor. Communication should be available.
    4. ⇒If communication is not available, test the serial data circuit between the JX209 splice pack terminal C and the inflatable restraint vehicle roll over sensor for a short to ground or a short to voltage. If the circuit tests normal, replace the inflatable restraint vehicle roll over sensor.

    Important: After each connection, cycle the ignition key off for 5 seconds, then ON before attempting to establish communication.

  4. Ignition OFF, with the jumper wire still attached to terminal H, individually move the other end of the jumper wire to each of the terminals listed below and attempt to communicate with the applicable module. Communications should be available with each module listed.
    5. • JX209 terminal F, rear seat audio
    • JX209 terminal B, inflatable restraint sensing and diagnostic module (SDM)
    • JX209 terminal D, digital radio receiver
    • JX209 terminal E, vehicle control interface module (VCIM)
    ⇒If any module does not communicate, test the serial data circuit between the applicable module harness connector and the JX209 harness connector for a short to ground or a short to voltage. If the circuit tests normal, replace the applicable module.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

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

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 200, 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 200 and JX 209 as common connection points between some modules and the data link connector (DLC).

Diagnostic Aids
    • Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they’re transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:
      • A control module on the data communication circuit was disconnected while the communication circuit is awake.
      • Power to one or more modules was interrupted during diagnosis
      • A low battery condition was present, so some control modules stop communicating when battery voltage drops below a certain threshold.
      • Battery power was restored to the vehicle and control modules on the communication circuit did not all re-initialize at the same time.
      • If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.
    • Do not replace a control module reporting a U-code. The U-code identifies which control module needs to be diagnosed for a communication issue.
    • Communication may be available between the BCM and the scan tool with the high speed GMLAN serial data system inoperative. This condition is due to the BCM using both the high and low speed GMLAN systems.
    • An open in the low speed GMLAN serial data circuit between the splice pack and a module will only affect that 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 but not communicate with the vehicle. When the scan tool attempts to communicate with the vehicle a message "no CANdi module detected" will be displayed.
    • An open between the DLC and JX 200 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.
    • Technicians may find various Local Area Network (LAN) communication Diagnostic Trouble Codes (DTC) and no low speed GMLAN communications with the scan tool.
        These conditions may be caused by the installation of an aftermarket navigation radio module (see bulletins). Some customers may comment of one or more of the following concerns:
       - Vehicle will not crank.
       - Vehicle cranks but will not start.
       - Vehicle stability enhancement system warning lights and messages.
       - PRNDL gear indicator position errors.
       - Tire Pressure Monitor (TPM) system warning lights.

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

Circuit/System Testing

Note: Use the schematic to identify the following:

   • Control modules the vehicle is equipped with
   • Control module locations on the low speed GMLAN serial data circuit
   • Each control module's low speed GMLAN serial data circuit terminals

  1. Attempt to communicate with all control modules on the low speed GMLAN serial data circuit, refer to Data Link References. Communications should not be available with two or more control modules on the low speed GMLAN serial data circuit.
    2. ⇒If only one control module is not communicating, diagnose that control module only, refer to DTC U0100-U0299.
    ⇒If one or more control modules are communicating but not all, refer to Testing the Serial Data Circuit for an Open/High Resistance.
  2. Disconnect the scan tool from the DLC. The following tests will be done at the DLC connector.
  3. All access doors closed, ignition OFF for 60 seconds, test for less than 10 Ω between the ground circuit terminal 5 and ground.
    4. ⇒If greater than the specified range, test the ground circuit for an open/high resistance.
  4. Ignition ON, test for less than 4.5 V between the serial data circuit terminal 1 and ground.
    5. ⇒If greater than the specified range, test the serial data circuit for a short to voltage, refer to Testing the Serial Data Circuit for a Short to Voltage.
  5. Ignition OFF for 60 seconds, test for greater than 100 Ω between the serial data circuit terminal 1 and ground.
    6. ⇒If not the specified value, test the serial data circuit for a short to ground, refer to Testing the Serial Data Circuits for a Short to ground.
  6. Disconnect the harness connector at the JX 200 splice pack.
  7. Test for less than 2 Ω between the serial data circuit terminal 1 and the JX 200 splice pack terminal H.
    8. ⇒If greater than the specified range, test the serial data circuit for an open/high resistance. If the circuits test normal, replace the splice pack.

Testing the Serial Data Circuits for a Short to Voltage

  1. Ignition OFF, disconnect the harness connectors at the JX 200 and JX 209 splice packs, as equipped.
  2. Ignition ON, test for less than 4.5 V between the DLC serial data circuit terminal 1 and ground.
    3. ⇒If greater than the specified range, repair the short to voltage.
  3. Test for less than 4.5 V between each serial data circuit and ground.
    4. ⇒If greater than the specified range, perform the appropriate test listed below:
    • Serial data circuits with one control module, test the serial data circuit for a short to voltage. If the circuit tests normal replace the control module.
    • Serial data circuits with 2 or more control modules, test each section of the serial data circuit for a short to voltage. If the circuits test normal, replace the control module that causes the short to voltage when connected.

Testing the Serial Data Circuits for a Short to Ground

  1. Ignition OFF, disconnect the harness connectors at the JX 200 and JX 209 splice packs, as equipped.
  2. Test for infinite resistance between the DLC serial data circuit terminal 1 and ground.
    3. ⇒If not the specified value, repair the short to ground.
  3. Ignition OFF for 60 seconds, test for greater than 100 Ω between each serial data circuit and ground.
    4. ⇒If less than the specified range, perform the appropriate test listed below:
    • Serial data circuits with one control module, test the serial data circuit for a short to ground. If the circuit tests normal replace the control module.
    • Serial data circuits with 2 or more control modules, test each section of the serial data circuit for a short to ground. If the circuits test normal, replace the control module that causes the short to ground when connected.

Testing the Serial Data Circuit for an Open/High Resistance

  1. If equipped with a JX 209 splice pack, ignition ON, verify the scan tool communicates with one or more control modules connected to the JX 209 splice pack.
    2. ⇒If all control modules on the JX 209 splice pack do not communicate, test the serial data circuit between the JX 200 and JX 209 splice packs for an open/high resistance. If the circuit tests normal, test each splice pack for an open/high resistance.
  2. Ignition OFF, disconnect one of the harness connectors listed below:
    3. • JX 200 if the control modules not communicating are connected to the JX 200 splice pack
    • JX 209 if the control modules not communicating are connected to the JX 209 splice pack, if equipped
  3. Install a 3A fused jumper wire between the disconnected splice pack terminal H and a low speed GMLAN serial data circuit that is not communicating.
  4. Ignition ON, verify the scan tool communicates with the control modules connected to the low speed GMLAN serial data circuit.
    5. ⇒If any control module does not communicate, test each section of the serial data circuit for an open/high resistance. If the circuits test normal, replace the control module that does not communicate when connected.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

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