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DTC P0720: Countershaft Speed Sensor Circuit

NOTE: Record pertinent freeze frame data before trouble shooting DTC.
  1. Connect OBD II scan tool to Data Link Connector (DLC). Turn ignition on. Check for DTCs P0107, P0108, P1128 or P1129. If any of these DTCs are present, go to appropriate diagnostic procedure under DIAGNOSTIC TESTS  in SELF-DIAGNOSTICS - 3.2TL article. After performing necessary repairs, recheck for presence of DTC P0720. If DTC P0720 is present, go to next step.
  2. Turn ignition off. Disconnect countershaft speed sensor harness connector. Turn ignition on. Use DVOM to measure voltage between harness connector Yellow/Red wire and ground. If around 5 volts are present, go to next step. If voltage is not as specified, go to step  7.
  3. Turn ignition off. Check for continuity to ground at speed sensor harness connector terminal No. 2 (Blue wire). If continuity is present, repair short circuit to ground between speed sensor harness connector terminal No. 2 and PCM connector "D" terminal No. 10 (Blue wire). See Figure. If continuity is not present, go to next step.
  4. Check for continuity to ground at speed sensor harness connector terminal No. 3 (Green wire). If continuity is present, go to next step. If continuity is not present, repair open circuit between speed sensor harness connector terminal No. 3 and PCM connector "D" terminal No. 16 (Green wire).
  5. Turn ignition on. Use DVOM to measure voltage between speed sensor harness connector terminals No. 2 (Blue wire) and 3 (Green wire). If voltage is around 5 volts, go to step  9. If voltage is not as specified, go to next step.
  6. With PCM connectors plugged in and ignition on, measure voltage between PCM harness connector "D" terminals No. 10 (Blue wire) and 16 (Green wire). If voltage is around 5 volts, repair open circuit between PCM harness connector "D" terminal No. 10 and speed sensor harness connector terminal No. 3 (Green wire). If voltage is not as specified, check for loose or corroded PCM connectors or terminals. Repair as necessary. If no problem was found, substitute known-good PCM and recheck system.
  7. Measure voltage between PCM harness connector "C" terminal No. 19 (Yellow/Red wire) and ground. See Figure. If voltage is between 4.75-5.25 volts, repair open circuit between PCM harness connector "C" terminal No. 19 and countershaft speed sensor harness connector terminal No. 1 (Yellow/Red wire). If voltage is not as specified, go to next step.
  8. Turn ignition off. Disconnect PCM connector "C". Use DVOM to check for continuity between PCM harness connector "C" terminal No. 19 (Yellow/Red wire) and ground. If continuity is present, repair short to ground in Yellow/Red wire between PCM harness connector "C" terminal No. 19 and countershaft speed sensor harness connector terminal No. 1. If no continuity is present, check for loose or corroded PCM connectors or terminals. Repair as necessary. If no problem was found, substitute known-good PCM and recheck system.
  9. Reconnect countershaft speed sensor connector. With ignition on, measure voltage between PCM harness connector "D" terminals No. 10 (Blue wire) and 16 (Green wire). If voltage is around 5 volts, go to next step. If voltage is not as specified, replace countershaft speed sensor.
  10. Raise and support front of vehicle. Set parking brake and block both rear wheels. Start engine, then shift to D5 position. Measure voltage between PCM harness connector "D" terminals No. 10 (Blue wire) and 16 (Green wire). See Figure. If voltage is around 1.5-3.5 volts, check for loose or corroded PCM connectors or terminals. Repair as necessary. If no problem was found, substitute known-good PCM and recheck system. If voltage is not as specified, replace countershaft speed sensor.
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