Scan Tool Does Not Communicate with Low Speed GMLAN Device
Scan Tool Does Not Communicate with Low Speed GMLAN Device
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.
Diagnostic Fault Information
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 JX200 and JX209 (splice pack combs) as a common connection between some modules and the DLC.
Diagnostic Aids
* Use the Date Link References (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 (U0100) 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 JX200 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 (Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector Views)
Description and Operation
Data Link Communications Description and Operation (Description and Operation)
Electrical Information Reference
* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)
Scan Tool Reference
Control Module References (Programming and Relearning) 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 (Diagnostic Trouble Code Descriptions) for diagnostics.
Circuit/System Testing
Low Speed GMLAN Initial Test
1. Test for less than 1.0 ohm of resistance between the DLC ground circuit terminal 5 and ground.
• If greater than 1.0 ohm, 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.
• 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.
• 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.
• 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.
• 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.
* Terminal G, instrument panel cluster (IPC)
* 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 harness 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.
• 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.
* 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 (Verification Tests) after completing the diagnostic procedure.
Control Module References (Programming and Relearning) for control module replacement, setup, and programming