Scan Tool Does Not Communicate With Sensing and Diagnostic Module

Scan Tool Does Not Communicate with Sensing and Diagnostic Module

Circuit Description

The provision for communicating with the inflatable restraint sensing and diagnostic control (SDM) is the data link connector (DLC). The DLC is located under the instrument panel. The DLC is used to link a scan tool to the SDM serial data stream. Some common uses of the scan tool are listed below:

- Identifying the stored diagnostic trouble codes (DTCs).
- Reading the serial data stream.
- Clearing the DTCs.
- Storing the Freeze Frame data.

Diagnostic Aids

Some scan tools may require an external power supply. Make sure your scan tool is using the correct power feed.

Ensure that the correct application (model year, carline, VIN code) has been selected on the scan tool. If communications are still not established, try the scan tool on another vehicle in order to ensure that the scan tool or the connecting cables are not the cause of the malfunction. Always try the scan tool on a vehicle that uses the same DLC terminal for serial data communication.

Any circuitry that is suspect to an intermittent complaint should be thoroughly inspected for the following:

- Backed-out terminals.
- Improper mating of terminals.
- Broken electrical connector locks.
- Improperly formed or damaged terminals.
- Faulty terminal-to-wiring connections.
- Physical damage to the wiring harness.
- A broken conductor inside the wire insulation.
- Corrosion of the electrical connections, the splices, or the terminals.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

4. This step checks whether the scan tool can communicate with other control modules on the vehicle. If the scan tool can communicate with the Power Train Control Module (PCM), then the DLC ground circuit (terminal 4) and the DLC ignition positive voltage circuit (terminal 16) are OK.
5. This step checks for an open in the serial data circuit between the SDM and the right instrument panel junction block or for a defective SDM.
6. This step checks for an open/short to ground circuit, a short to battery positive circuit, or for a defective scan tool.
7. The modules supply a low current (about 1.85 mA) on the serial data circuit. The normal circuit low current will NOT illuminate a test lamp. If the circuit is shorted to battery positive the higher current will illuminate the test lamp.
10. The scan tool may be damaged by high current flow on the serial data circuit at DLC terminal 7. Verify the scan tool for proper operation on a known good vehicle that uses terminal 7 of the DLC for serial data communication.