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 trouble codes (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
- If a short to B+ is present, a history U1301 or U1305 will set in the modules. Refer to DTC U1300, U1301, or U1305.
- If a short to ground is present, a history U1300 or U1305 will set in the modules. Refer to DTC U1300, U1301, or U1305.
- Disconnecting modules and turning the ignition switch to RUN may cause DTCs in these modules. Check for DTCs in each module upon completion of the required repair.
- The scan tool cannot directly communicate to the rear video/audio/HVAC or video disc player. Diagnosis is accomplished by checking communications with the radio.

TEST DESCRIPTION

Steps 1 - 11:

Steps 12 - 19:

Steps 20 - 27:

Steps 28 - 37:

The numbers below refer to the step numbers on the diagnostic table.
2. 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.
3. DTCs U1300, U1301, or U1305 may be retrieved with a history status. These DTCs are not the cause of the present condition.
6. A state of health DTC with a history status may be present along with a U1000 having a current status. This indicates the malfunction occurred when the ignition was ON.
7. Data link connector terminals 2 and 5 provide the connection to the class 2 serial data circuit and the signal ground circuit respectively.
9. A poor connection at the DLC terminal would cause this condition but will not set a DTC.
10. An open in the class 2 serial data circuit between the DLC and the star connector will prevent the scan tool from communicating with any module. This condition will not set a DTC.
11. The class 2 serial data circuit is shorted to voltage or ground. The condition may be due to the wiring or due to a malfunction in one of the modules. When testing the wiring for a short, make sure there is not a module connected to the wire being tested. This test isolates the powertrain control module (PCM) class 2 serial data circuit.
13. This test isolates the inflatable restraint sensing and diagnostic module (SDM) class 2 serial data circuit.
15. This test isolates the electronic brake control module (EBCM) class 2 serial data circuit.
17. This test isolates the instrument panel cluster (IPC) class 2 serial data circuit.
19. This test isolates the theft deterrent control module class 2 serial data circuit.
21. This test isolates the driver information center (DIC) class 2 serial data circuit.
23. This test isolates the radio class 2 serial data circuit.
33. If there are no current DTCs that begin with a U, the communication malfunction has been repaired.
35. The communication malfunction may have prevented diagnosis of the customer complaint.