P0721
DTC P0721: Problem in Countershaft Speed Sensor CircuitNOTE:
^ Record all freeze data and review General Troubleshooting Information before you troubleshoot.
^ This code is caused by an electrical circuit problem and cannot be caused by a mechanical problem in the transmission.
1. Record all freeze data, and clear the DTC with the HDS.
2. Raise the front of the vehicle, make sure it is securely supported, and allow the front wheels to rotate freely.
3. Start the engine, drive the vehicle in the [D] position, and hold the vehicle at speeds over 30 mph (48 km/h) for more than 10 seconds. Slow down and stop the wheels.
4. Check the OBD STATUS in DTCs MENU for a pass/fail test of code P0721.
Did the result indicate a fail?
YES - Go to step 5.
NO - Intermittent failure, the system is OK at this time. Check for poor connections or loose terminals at the countershaft speed sensor and PCM. If the tester indicates NOT COMPLETE, return to step 3 and recheck.
5. Turn the ignition switch OFF.
6. Jump the SCS line with the HDS.
7. Disconnect PCM connector A (31P) and countershaft speed sensor connector.
8. Check for continuity between PCM connector terminals A8 and body ground, and between A9 and body ground.
Is there continuity?
YES - Go to step 9.
NO - Repair open in the wire between PCM connector terminals A8, A9 and ground (G101), or repair poor ground (G101), then go to step 29.
9. Connect PCM connector A (31P).
10. Turn the ignition switch ON (II).
11. Measure the voltage between countershaft speed sensor connector terminal No. 1 and body ground.
Is there about 5 V?
YES - Go to step 12.
NO - Go to step 23.
12. Turn the ignition switch OFF.
13. Disconnect PCM connector A (31P).
14. Check for continuity between countershaft speed sensor connector terminal No. 2 and body ground.
Is there continuity?
YES - Repair short to ground in the wire between PCM connector terminal A18 and the countershaft speed sensor, then go to step 29.
NO - Go to step 15.
15. Check for continuity between countershaft speed sensor connector terminal No. 3 and body ground.
Is there continuity?
YES - Go to step 16.
NO - Repair open in the wire between the countershaft speed sensor and ground (G101), or repair poor ground (G101), then go to step 29.
16. Connect PCM connector A (31P).
17. Turn the ignition switch ON (II)
18. Measure the voltage between countershaft speed sensor connector terminals No. 2 and No. 3.
Is there about 5 V?
YES - Go to step 19.
NO - Go to step 28.
19. Connect countershaft speed sensor connector.
20. Measure the voltage between PCM connector terminals A18 and A8 or A9.
Is there 0 V or about 5 V?
YES - Go to step 21.
NO - Replace the countershaft speed sensor, then go to step 23.
21. Shift to the [P] position. Start the engine, and let it idle.
22. Shift to the [D] position, and measure the voltage between PCM connector terminals A18 and A8 or A9.
Is there 1.5 V - 3.5 V?
YES - Update the PCM if it does not have the latest software, or substitute a known-good PCM, then recheck. If the symptom/indication goes away with a known-good PCM, replace the original PCM.
NO - Replace the countershaft speed sensor, then go to step 29.
23. Measure the voltage between PCM connector terminals A20 and A8 or A9.
Is there 4.75 V - 5.25 V?
YES - Repair open in the wire between PCM connector A20 and the countershaft speed sensor, then go to step 29.
NO - Go to step 24.
24. Turn the ignition switch OFF.
25. Jump the SCS line with the HDS.
26. Disconnect PCM connector A (31P).
27. Check for continuity between PCM connector terminal A20 and body ground.
Is there continuity?
YES - Repair short to ground in the wire between PCM connector terminal A20 and the countershaft speed sensor, then go to step 29.
NO - Check for loose or poor connections at PCM connector terminal A20. If the connection is OK, update the PCM if it does not have the latest software, or substitute a known-good PCM, then recheck. If the symptom/indication goes away with a known-good PCM, replace the original PCM.
28. Measure the voltage between PCM connector terminals A18 and A8 or A9.
Is there about 5 V?
YES - Repair open in the wire between PCM connector terminal A18 and the countershaft speed sensor, then go to step 29.
NO - Update the PCM if it does not have the latest software, or substitute a known-good PCM, then recheck. If the symptom/indication goes away with a known-good PCM, replace the original PCM.
29. Clear the DTC with the HDS.
30. Test-drive the vehicle for several minutes under the same conditions as those indicated by the freeze data.
31. Check the OBD STATUS in DTC's MENU for a pass/fail test of code P0721.
Did the result indicate a pass?
YES - The problem has been corrected.
NO - Return to step 1 and recheck.