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.
The engine will not start when there is a total loss of class 2 serial data communication while the ignition is OFF. The following conditions will cause a total loss of class 2 serial data communication:
• | A class 2 serial data circuit shorted to ground |
• | A class 2 serial data circuit shorted to voltage |
• | An internal condition within a module or connector on the class 2 serial data circuit, that causes a short to voltage or ground to the class 2 serial data circuit |
The numbers below refer to the step numbers on the diagnostic table.
A partial malfunction in the class 2 serial data circuit uses a different procedure from a total malfunction of the class 2 serial data circuit. The engine control module (ECM) and the transmission control module (TCM) communicate functionally on both high speed GMLAN and class 2 serial data circuits. The ECM and TCM communicate with the scan tool on high speed GMLAN only. The auxiliary gage center, w/ERG or ERH, is on class 2 serial data bus but doesn't have diagnostic capability. The following modules communicate with the scan tool on the class 2 serial data circuit:
• | The audio amplifier (AMP), w/Bose |
• | The body control module (BCM) |
• | The electronic brake control module (EBCM) |
• | The inflatable restraint sensing and diagnostic module (SDM) |
• | The instrument panel cluster (IPC) |
• | The memory seat module (MSM) - driver, w/AAB |
• | The radio |
• | The remote control door lock receiver (RCDLR) |
• | The roof/door module (RDM) |
The following DTCs may be retrieved with a history status, but are not the cause of the present condition.
• | U1300 |
• | U1301 |
• | U1305 |
A state of health DTC with a history status may be present along with a U1000 or U1255 code having a current status. This indicates that the malfunction occurred when the ignition was ON.
Data link connector terminals 2 and 5 provide the connection to the class 2 serial data circuit and the signal ground circuit respectively.
A poor connection at the DLC terminal of the splice pack SP201 would cause this condition but will not set a DTC.
An open or a short in the class 2 serial data circuit between the DLC and splice pack SP201 will prevent the scan tool from communicating with any module. This condition will not set a DTC.
Step | Action | Yes | No | ||||
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Schematic Reference: Data Link Connector Schematics Connector End View Reference: Master Electrical Component List in Wiring Systems | |||||||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | ||||
2 | Retrieve DTCs from the engine control module (ECM). Did you record DTCs U1300 or U1301? | Go to Step 3 | |||||
Does the scan tool communicate with any module on the class 2 serial data circuit? | Go to Step 4 | Go to Step 9 | |||||
Did you record any DTCs in the range of U1000 to U1305? | Go to Step 5 | Go to Step 8 | |||||
5 | Are the history DTCs U1300, U1301, or U1305 retrieved from any module? | Go to Step 6 | Go to Step 7 | ||||
6 |
Important:: Turn ON the ignition, with the engine OFF, when testing for a short to voltage. Use the DMM MIN/MAX function to capture intermittent conditions. Test the class 2 serial data circuit for an intermittent short to ground or an intermittent short to voltage. Refer to the following in Wiring Systems:
Did you find and correct the condition? | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | -- | ||||
Are U1000 or U1255 the only DTCs displayed in the previously specified range? | Go to DTC U1000 and U1255 | Go to DTC U1001-U1254 | |||||
Diagnose the non-communicating module by using the DTC U1001-U1254 procedure for the module which is not communicating. Refer to DTC U1001-U1254 . Did you complete the action? | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | -- | |||||
9 |
Did you find and correct the condition? | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | Go to Step 10 | ||||
10 | Test the DLC ground circuit at terminal 5 for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | Go to Step 11 | ||||
Did you find and correct the condition? | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | Go to Step 12 | |||||
Repair the class 2 serial data circuit between the splice pack SP201 and DLC for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you complete the repair? | System OK | -- |