Test B: Scan Tool Does Not Communicate With Powertrain Control Module

1. If engine controls diagnostic system check has been performed, go to next step. If engine controls diagnostic system check has not been performed, perform engine controls diagnostic system check. See ENGINE CONTROLS DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
2. Connect scan tool to Data Link Connector (DLC). DLC is located under left side of instrument panel, right of steering column. Turn ignition switch to RUN position. Attempt to communicate with Powertrain Control Module (PCM). If scan tool does not communicate with PCM, go to next step. If scan tool communicates with PCM, system is okay.
3. Attempt communicate with Sensing and Diagnostic Module (SDM). If scan tool does not communicate with SDM, go to next step. If scan tool communicates with SDM, go to step  6 .
4. Disconnect scan tool from DLC. Measure voltage between ground and DLC terminal No. 7 (White wire). See Figure . If battery voltage exists, go to next step. If battery voltage does not exist, go to step  15 .
5. Connect a test light between ground and DLC terminal No. 7 (White wire). If test light illuminates, go to step  20 . If test light does not illuminate, go to step  21 .
6. If vehicle is equipped with 3-speed automatic transmission or manual transmission, go to next step. If vehicle is equipped with a 4-speed automatic transmission, go to step  8 .
7. Turn ignition switch to LOCK position. Disconnect PCM 22-pin harness connector C3. PCM is located in front of center console, under radio. Turn ignition switch to RUN position. Measure voltage between ground and PCM harness connector C3 terminal No. 17 (White wire). See Fig 1 . If battery voltage exists, go to step  9 . If battery voltage does not exist, go to step  19 .
8. Turn ignition switch to LOCK position. Disconnect PCM 22-pin harness connector C4. PCM is located in front of center console, under radio. Turn ignition switch to RUN position. Measure voltage between ground and PCM harness connector C4 terminal No. 11 (White wire). See Fig 2 . If battery voltage exists, step  10 . If battery voltage does not exist, go to step  19 .
9. Turn ignition switch to LOCK position. Connect PCM harness connector. Turn ignition switch to RUN position. Measure voltage between ground and PCM harness connector C3 by backprobing terminal No. 12 (Black wire). See Fig 1 . If battery voltage does not exist, go to step  11 . If battery voltage exists, go to step  22 .
10. Turn ignition switch to LOCK position. Reconnect PCM harness connector. Turn ignition switch to RUN position. Measure voltage between ground and PCM harness connector C4 terminal No. 16 (Black wire). See Fig 2 . If battery voltage does not exist, go to next step. If battery voltage exists, go to step  22 .
11. Turn ignition switch to START position. If engine starts and runs, go to next step. If engine does not start and run, diagnose ignition relay circuit. See appropriate BASIC DIAGNOSTIC PROCEDURES article in ENGINE PERFORMANCE.
12. If vehicle is equipped with 3-speed automatic transmission or manual transmission, go to next step. If vehicle is equipped with a 4-speed automatic transmission, go to step  14 .
13. Remove EFI relay. EFI relay is located in fuse and relay box No. 1. See Figure . Measure resistance in Black wire between EFI relay connector terminal No. 10 and PCM harness connector C3 terminal No. 12. See Figure and Fig 1 . Battery voltage should exist. Turn ignition switch to LOCK position. Measure resistance between ground and PCM harness connector C1 terminals No. 13, 14 and 26 (all Brown wires). Measure resistance between ground and PCM harness connector C2 terminal No. 8 (Brown wire). See Fig 1 . Resistance should be less than 2 ohms. If any reading is not as specified, repair open in appropriate wire. See WIRING DIAGRAMS  . If all readings are as specified, go to step  23 .
14. Remove EFI relay. EFI relay is located in fuse and relay box No. 1. See Figure . Measure resistance in Black wire between EFI relay connector terminal No. 10 and PCM harness connector C4 terminal No. 16. See Figure and Fig 2 . Battery voltage should exist. Measure resistance between ground and PCM harness connectors C1, terminals No. 21 and 31 (both Brown wires). Measure resistance between ground and C2 terminals No. 8 and 17 (both Brown wires). See Fig 2 . Resistance should be less than 2 ohms. If either reading is not as specified, repair open in appropriate wire. See WIRING DIAGRAMS  . If readings are as specified, go to step  23 .
15. If vehicle is equipped with 3-speed automatic transmission or manual transmission, go to next step. If vehicle is equipped with a 4-speed automatic transmission, go to step  17 .
16. Turn ignition switch to LOCK position. Disconnect PCM 22-pin harness connector C3. PCM is located in front of center console, under radio. Measure resistance in White wire between PCM harness connector C3 terminal No. 17 and DLC terminal No. 7. See Figure and Fig 1 . If resistance is less than 2 ohms, go to step  18 . If resistance is 2 ohms or more, repair open in White wire between DLC and PCM. After repair, go to step  2 .
17. Turn ignition switch to LOCK position. Disconnect PCM 22-pin harness connector C4. PCM is located in front of center console, under radio. Measure resistance in White wire between PCM harness connector C4 terminal No. 11 and DLC terminal No. 7. See Figure and Fig 2 . If resistance is less than 2 ohms, go to next step. If resistance is 2 ohms or more, repair open in White wire between DLC and PCM. After repair, go to step  2 .
NOTE: Serial data circuit is connected to DLC, EBCM, PCM and SDM. It may be necessary to disconnect each module to ensure module is not internally grounded. For circuit identification, see DATA LINK COMMUNICATIONS article in WIRING DIAGRAMS.
18. Repair short to ground in serial data circuit. After repair, go to step  2 .
19. Repair open in Serial data circuit. After repair, go to step  2 .
NOTE: Serial data circuit is connected to DLC, EBCM, PCM and SDM. It may be necessary to disconnect each module to ensure module is not internally shorted to voltage. For circuit identification, see DATA LINK COMMUNICATIONS article in WIRING DIAGRAMS.
20. Repair short to voltage in serial data circuit. Scan tool damage may have occurred. After repair, go to step  2 .
21. Verify all scan tool selections are correct such as model year, model line, vehicle identification number and transmission. If all selections are correct and scan tool does not display any PCM data, replace defective scan tool. After repair, go to step  2 .
22. Disconnect fuel tank pressure sensor 3-pin harness connector. Fuel tank pressure sensor is located under rear of vehicle near EVAP canister. Disconnect Throttle Position (TP) sensor 3-pin harness connector. TP sensor is mounted on rear of throttle body. Measure voltage between ground and fuel tank pressure sensor harness connector terminal No. 2 (Blue wire). Measure voltage between ground and TP sensor harness connector terminal No. 3 (Light Green wire). If voltage is 5 volts or more at both terminals, go to next step. If voltage is less than 5 volts at either terminal, repair open or short to ground in appropriate wire between PCM and suspect component. See ENGINE PERFORMANCE article in WIRING DIAGRAMS.
23. Inspect PCM harness connector for loose, corroded terminals or intermittent condition. See PROBLEM DIAGNOSIS  under INTERMITTENTS. If concern still exists, go to next step. If concern does not exist, go to step  2 .
24. Replace PCM. After repair, go to step  2 .

Fig 1: Identifying 3-Speed Automatic Transmission & Manual Transmission Powertrain Control Module Harness Connector Terminals

Fig 2: Identifying 4-Speed Automatic Transmission Powertrain Control Module Harness Connector Terminals