Scan Tool Does Not Communicate with Class 2 Device
Scan Tool Does Not Communicate with Class 2 Device
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.
Diagnostic Fault Information
Circuit/System Description
Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. Connecting a scan tool to the data link connector (DLC) allows communication with the modules for diagnostic purposes. DTCs may be set due to this symptom and during this diagnostic procedure. Complete the diagnostic procedure in order to ensure all the DTCs are diagnosed and cleared from memory.
Diagnostic Aids
* The body control module (BCM) detects that the ignition is ON and sends the appropriate power mode message to the other modules. Therefore, the BCM must be connected to the DLC for any other module to communicate with the scan tool.
* This test is used for a total class 2 serial data 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 U1001-U1254 (U1001) for diagnostics.
* The following conditions may cause a total loss of class 2 serial data communication:
^ The class 2 serial data circuit shorted to ground or voltage.
^ A module internal malfunction that causes a short to voltage or ground on the class 2 serial data circuit.
Reference Information
Schematic Reference
* Data Communication Schematics ([1][2]Electrical Diagrams)
* Control Module References (Control Module References)
Connector End View Reference
Component Connector End Views (Component Connector End Views)
Description and Operation
Data Link Communications Description and Operation (Description and Operation)
Electrical Information Reference
* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)
Scan Tool Reference
Control Module References (Control Module References) for Scan Tool Information
Circuit/System Testing
Class 2 Communication Initial Test
1. Test for less than 1 ohm between the DLC ground circuit terminal 5 and ground.
• If greater than the specified range, test the ground circuit for open/high resistance.
2. Ignition OFF, disconnect the harness connector of JX305 and attempt to communicate with the BCM. Communication should not be available.
• If communication is available, refer to JX305 Test.
3. Ignition OFF, disconnect the harness connector of JX205.
4. Ignition ON, test for less than 1 volt between the serial data circuit terminal H of JX205 and ground.
• If greater than the specified range, test the serial data circuit for a short to voltage.
5. Test for infinite resistance between the serial data circuit terminal H of JX205 and ground.
• If less than the specified value, test the serial data circuit for a short to ground.
6. Ignition ON, test for less than 1 volt between the serial data circuit terminal A of JX205 and ground.
• If greater than the specified range, test the serial data circuit for a short to voltage.
7. Test for infinite resistance between the serial data circuit terminal A of JX205 and ground.
• If less than the specified value, test the serial data circuit for a short to ground.
8. Test for less than 1 ohm on the serial data circuit between terminal A of JX205 and terminal 2 of the DLC.
• If greater than the specified range, test the serial data circuit for open/high resistance.
9. Ignition OFF, disconnect the harness connectors X1 and X3 of the BCM
10. Verify a test lamp illuminates between each ground circuit terminal of the BCM listed below and B+.
* X3 - A11
* X3 - B11
• If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
11. Ignition ON, verify a test lamp illuminates between each voltage circuit terminal of the BCM listed below and ground.
* X1 - A3
* X1 - A19
* X3 - A1
* X3 - A2
* X3 - A20
* X3 - B4
* X3 - B13
* X3 - B15
* X3 - B17
* X3 - B18
• If the test lamp does not illuminate, test the voltage circuit for an open/high resistance or short to ground.
12. Ignition OFF, connect the harness connectors of the BCM.
13. Ignition OFF, connect a 3-amp fused jumper wire between terminal A and terminal M of JX205. Attempt to communicate with the BCM. Communication should be available.
• If communication is not available, test the serial data circuit for a short to voltage, or short to ground between the BCM and JX205. If the circuits test normal, replace the BCM.
Important: After each connection, wait for 5 seconds to determine that communication remains available.
14. Connect another 3-amp fused jumper wire to terminal A of JX205. Individually connect the other end of the jumper wire to each other terminal of JX205 and verify that communication remains available to the BCM.
• If communication is interrupted, test the serial data circuit between JX205 and the last module connected for a short to ground or a short to voltage. If the circuit tests normal, replace the module that caused no communication.
JX305 Test
1. Ignition OFF, connect a 3-amp fused jumper wire to terminal M of JX305.
Important: After each connection, wait for 5 seconds to determine that communication remains available.
2. While communicating with the BCM, individually move the other end of the jumper wire to each of the terminals of JX305 and verify that communication remains available to the BCM.
• If communication is interrupted, test the serial data circuit between JX305 and the last module connected for a short to ground or a short to voltage. If the circuit tests normal, replace the module that caused no communication.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the repair.
* Control Module References (Control Module References) for module replacement, setup, and programming
* GMLAN Wiring Repairs (GMLAN Wiring Repairs)