Scan Tool Does Not Communicate With Class 2 Device
Scan Tool Does Not Communicate with Class 2 DeviceCircuit Description
The engine control module (ECM), transmission control module (TCM) and electronic hydraulic control unit (EHCU) [ABS module] all communicate with the scan tool over the Class 2 serial data link. The EHCU receives transmission parameters necessary for correct ABS functions over the Class 2 link as well. However, the ECM and TCM communicate with each other over the controller area network (CAN) link. The CAN link is not used for communication with the scan tool and is shared only between the ECM and TCM.
Diagnostic Aids
The following conditions will cause a loss of class 2 serial data communication between the TCM and EHCU or between the scan tool and any control module:
- A Class 2 serial data circuit open.
- 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.
- Open ground circuit (pin 5) at the DLC.
The Class 2 Message Monitor may be used to determine if a control module is intermittently communicating over the Class 2 link. The scan tool will indicate INACTIVE if a module is not communicating with the ignition turned ON.
NOTE: If the control module does not communicate as soon as the ignition is turned ON, that module will not be appear on the scan tool until it initially communicates. Therefore, if the scan tool indicates INACTIVE for a module or does not display the module with the ignition ON, the module is not communicating on the Class 2 link.
Scan Tool Does Not Communicate with Class 2 Device
Schematic Reference: Engine Controls Schematics
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