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 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. DTCs may 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 DLC and body control module (BCM) are on a common terminal on the junction block - left instrument panel (I/P).

The class 2 serial data circuit for the electronic brake control module (EBCM) and sensing and diagnostic module (SDM) are on a common terminal on the junction block - left I/P.

The class 2 serial data circuit for the vehicle theft deterrent (VTD) and radio are on a common terminal on the junction block - left I/P.

The class 2 serial data circuit for the instrument panel cluster (IPC) and powertrain control module (PCM) are on a common terminal on the junction block - left I/P.

TEST DESCRIPTION

Steps 1-8:

Steps 9-13:

Steps 14-19:

Steps 20-24:

Steps 25-29:

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.
4. DTCs U1300, U1301, and 1305 may be retrieved with a history status. These DTCs are not the cause of the present condition.
5. When testing for shorts to B+, the tests must be run with ignition switch in the RUN position.
6. A state of health DTC (U1XXX) with a history status may be present along with a U1000 or U1255 having a current status. This indicates the malfunction occurred when the ignition was ON.
7. DLC terminals 2 and 5 provide the connection from the vehicles class 2 serial data circuit and the Tech 2. A poor connection at this connector could cause corrupted data transmissions between the 2 devices. Pin 2 is the signal terminal and pin 5 is the signal ground terminal.
9. This step tests for an open from pin 2 of the DLC connector and the fuse block - left I/P harness connector. It also tests for a short to B+ and ground between the fuse block - left I/P stationary junction terminals.
10. This is an active test of the class 2 serial data circuit with the BCM being isolated from the communication bus, from the procedures in step 9. If you are able to communicate with the class 2 serial data circuit, the BCM should be replaced.
11. This is an active test of the class 2 serial data circuit with the IPC isolated from the communication bus. If you are able to communicate with the class 2 serial data circuit during this step, the IPC should be replaced.
12. This is an active test of the class 2 serial data circuit with the SDM isolated from the communication bus. If you are able to communicate with the class 2 serial data circuit during this step, the SDM should be replaced.
13. This is an active test of the class 2 serial data circuit with the radio isolated from the communication bus. If you are able to communicate with the class 2 serial data circuit during this step, the radio should be replaced.
14. This is an active test of the class 2 serial data circuit with the digital radio receiver isolated from the communication bus. If you are able to communicate with the class 2 serial data circuit during this step, the digital radio receiver should be replaced. Not all vehicles are equipped with this device.
15. This is an active test of the class 2 serial data circuit with the EBCM isolated from the communication bus. If you are able to communicate with the class 2 serial data circuit during this step, the EBCM should be replaced.
16. This is an active test of the class 2 serial data circuit with the PCM isolated from the communication bus. If you are able to communicate with the class 2 serial data circuit during this step, the PCM should be replaced. The SDM is reconnected to allow at least one possible module for the Tech 2 to communicate with.
18. This is an active test of the class 2 serial data circuit with the remote control door lock receiver (RCDLR), if the vehicle is equipped, isolated from the communication bus. If you are able to communicate with the class 2 serial data circuit during this step, the RCDLR should be replaced.
20. This is an active test of the class 2 serial data circuit with the VTD, if the vehicle is equipped, isolated from the communication bus. If you are able to communicate with the class 2 serial data circuit during this step, the VTD should be replaced.
21. This step isolates all the modules from the class 2 serial data circuit and tests for a short to B+ or ground. The harness connector to the fuse block - left I/P must be installed and ignition switch placed in the RUN position in order to supply the B+ circuits routed throughout the vehicle.
22. In this step instructions are given to analyze each branch of the class 2 serial data circuit, in order to isolate the cause of the short.
25. If there are no current DTCs that begin with a "U", the communication malfunction has been repaired.
27. The communication malfunction may have prevented diagnosis of the customer complaint.