Scan Tool Does Not Communicate with Class 2 Device

Scan Tool Does Not Communicate with Class 2 Device

Circuit 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.

Diagnostic Aids

The engine will not start when there is a total loss of class 2 serial data communication while the ignition is OFF. The serial data bus can not be used to analyze a malfunction on the class 2 serial data bus. The following conditions will cause a total loss of class 2 serial data communication:

* A class 2 serial data circuit shorted to ground. A history U1300 will set in all modules. Refer to DTC U1300, U1301, or U1305. U1300 U1301 U1305
* A class 2 serial data circuit shorted to voltage. A history U1301 will set in all modules. Refer to DTC U1300, U1301, or U1305. U1300 U1301 U1305
* 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.

Test Description

Step 1 - Step 10:

Step 11 - Step 15:

Step 16 - Step 22:

The numbers below refer to the step numbers on the diagnostic table.
2. A partial loss of communication in the class 2 serial data circuit uses a different procedure than a total loss of communication of the class 2 serial data circuit.
4. The following DTCs may be retrieved with a history status. These DTCs are not the cause of the present condition.
* U1300
* U1301
* U1305
6. A State of Health (SOH) DTC with a history status may be present along with a U1000 or U1255 with a current status. This indicates that the malfunction occurred when the ignition was on.
10. Normal class 2 serial data communication cannot take place until the power mode master (PMM) module sends the appropriate power mode message. If the PMM does not send a wake-up message, other modules on the class 2 serial data circuit may not communicate.
12. This step will isolate a wiring problem or a module malfunction.
13. An open circuit at this point will cause a loss of communication with the vehicle.
14. This step analyzes the specific branch circuit for a malfunction.
19. If there are no current DTCs that begin with the letter "U", the communication concern has been repaired.
20. The communication concern may have prevented diagnosis of the customer complaint.