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Test Description
The numbers below refer to the step numbers on the diagnostic table.
1. The OBD fuse supplies power to terminal 16 of the DLC.
4. The battery positive voltage and ground circuits of the DLC are functioning properly. The malfunction must be due to the scan tool.
Scheme 7
The numbers below refer to the step numbers on the diagnostic table.
3. This step checks whether the scan tool can communicate with other control modules on the vehicle. If the scan tool can communicate with one of the other modules then the DLC connector, the shared circuits, and the scan tool are OK.
5. The modules supply a low current (about 1.85 mA) voltage 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.
7. This step checks whether the PCM is receiving ignition positive voltage from the EFI relay when the ignition is ON. The PCM cannot provide serial data without ignition positive voltage from the EFI relay.
8. If the engine starts and runs, the EFI relay is OK.
9. The PCM cannot provide serial data without the correct power and grounds.
13. The scan tool may be damaged by high current flow on the serial data circuit at DLC terminal 7. Inspect the scan tool for proper operation on a known good vehicle that uses terminal 7 of the DLC for serial data communication.
15. A shorted sensor reference voltage circuit can cause a loss of scan tool communication with the PCM.
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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 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 BPMV and the right instrument panel junction block or for a defective BPMV.
6. This step checks for an open/shorted to ground circuit, a shorted 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.
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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 shot 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.
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Data Link Communications Description and Operation
The scan tool accesses the following data lines
- The brake pressure control valve (BPMV), on vehicles with antilock brake systems
- The powertrain control module (PCM)
- The Inflatable Restraint Sensing and Diagnostic Control Module (SDM)
The BLU/RED wire at cavity 7 of the data link connector (DLC) OBD 2 provides access to the BPMV, SDM, and to the PCM. The RED/BLK wire at cavity 16 provides voltage to the scan tool. The WHT/BLK wire at cavity 4 and the BRN/RED wire at cavity 5 provides ground to the scan tool.
The data lines monitor the module for diagnostic purposes and for diagnostic trouble codes (DTCs).