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 DLC allows communication with the modules for diagnostic purposes. Diagnostic trouble codes (DTC) 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
The engine will not start when there is a total malfunction of the class 2 serial data circuit while the engine is not running.

The class 2 serial data circuit for the EBCM and PCM are on a common terminal on the LH IP junction block.

The class 2 serial data circuit for the BCM and SDM are on a common terminal on the LH IP junction block.

The class 2 serial data circuit for the DLC and IRC are on a common terminal on the LH IP junction block.

TEST DESCRIPTION

Steps 1-4:

Steps 5-10:

Steps 11-15:

Steps 16-21:

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 and/or U1301 may be retrieved with a history status. These DTCs are not the cause of the present condition.
4. 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.
5. Data link connector terminals 2 and 5 provide the connection to the class 2 serial data circuit and the signal ground circuit respectively.
7. A poor connection, short to ground or B+ at this point would cause this condition but may not set a DTC. Because the DLC and IRC share the same terminal at LH IP, the IRC must be taken out of the class 2 serial data circuit.
8. An open in the class 2 serial data circuit between the DLC and the left IP junction block connector will prevent the scan tool from communicating with any module. This condition may not set a DTC.
9. This test isolates the EBCM from the class 2 serial data circuit.
10. This test isolates the PCM from the class 2 serial data circuit.
11. This test isolates the BCM from the class 2 serial data circuit.
12. This test isolates the IRC from the class 2 serial data circuit.
13. This test isolates the SDM from the class 2 serial data circuit.
14. This test checks for a wiring problem.
17. If there are no current DTCs that begin with a "U", the communication malfunction has been repaired.
19. The communication malfunction may have prevented diagnosis of the customer complaint.