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 following conditions will cause a class 2 serial data communication malfunction:
- The body control module (BCM) detects that the ignition switch is ON and sends the appropriate power mode message to the other modules connected to the class 2 serial data circuit. The BCM must be connected to the class 2 serial data circuit for many other modules to communicate with the scan tool.
- A class 2 serial data circuit shorted to ground. A history U1300 will set in all modules. Refer to DTC U1300, U1301, or 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.
- A class 2 serial data circuit shorted to ground or voltage. A history U1305 will set in all modules. Refer to DTC U1300, U1301, or 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.
- If the malfunction is intermittent check for poor connections at the suspect module. Wiggling the harness wiring may help in locating the fault.

TEST DESCRIPTION

Steps 1-10:

Steps 11-17:

Steps 18-22:

The numbers below refer to the step numbers on the diagnostic table.
3. 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.
5. The following DTCs may be retrieved with a history status. These DTCs are not the cause of the present condition.
- U1300
- U1301
- U1305
7. A State of Health DTC with a history status may be present along with a U1000 with a current status. This indicates that the malfunction occurred when the ignition was ON.
11. This step will isolate a wiring problem or a module malfunction.
13. This step analyzes the specific branch circuit for a malfunction.
14. An open circuit at this point will cause a loss of communication with the vehicle.
19. If there are no current DTCs that begin with the letter U, the communication concern has been repaired.
21. The communication concern may have prevented diagnosis of the customer complaint.