Diagnostic Procedures

Perform powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.

NOTE: Support lower control arms in normal horizontal position to avoid damage to drive axles. Do not operate vehicle in gear with wheels hanging down at full travel.

Install a scan tool. Turn ignition on, engine off. Record FREEZE FRAME/FAILURE RECORDS. Clear DTCs. Raise and support drive wheels. Start and idle engine. Place transmission in Drive. Monitor transmission VSS on scan tool. With drive wheels rotating, increase and decrease throttle position. If VSS RPM increases when wheel speed increases, see INTERMITTENT TROUBLE CODE DETERMINATION under ON-BOARD DIAGNOSTICS under SELF-DIAGNOSTIC SYSTEM. If VSS RPM does not increase when wheel speed increases, go to next step.
Turn ignition off. Disconnect PCM connector C1. Connect DVOM between PCM connector C1 terminals No. 64 (Yellow wire) and No. 65 (Purple wire). See Figure. Select AC volts on DVOM. Turn ignition on, engine off. Place range selector in a DRIVE range or NEUTRAL. Rotate right front drive wheel by hand, while observing DVOM display. If voltage is more than 0.4 volt AC, go to step 15. If voltage is not more than 0.4 volt AC, go to next step.
Leave DVOM connected to PCM connector. Select ohms on DVOM. Measure resistance of complete VSS circuit. If resistance is 1650-3180 ohms, go to step 8. If resistance is not 1650-3180 ohms, go to next step.
If resistance is more than 3180 ohms, go to step 11. If resistance is not more than 3180 ohms, go to next step.
Leave DVOM connected to PCM connector. Disconnect VSS connector at transmission. Check for Yellow wire and Purple wire shorted together. If problem was found, go to next step. If problem was not found, go to step 14.
Repair short between Yellow wire and Purple wire between VSS and PCM. After repairs, go to step 16.
Check Yellow wire between VSS and PCM for short to ground. If problem was found, repair as necessary. After repairs, go to step 16. If problem was not found, go to next step.
Reconnect PCM connector C1. Select DC volts on DVOM. Connect DVOM between VSS connector terminals. Turn ignition on, engine off. If DVOM displays more than one volt, go to next step. If DVOM does not display more than one volt, go to step 13.
Repair short to power in Yellow wire between VSS and PCM. After repairs, go to step 16.
Check Yellow wire between VSS and PCM for open. If problem was found, repair as necessary. After repairs, go to step 16. If problem was not found, go to next step.
Check Purple wire between VSS and PCM for open. If problem was found, repair as necessary. After repairs, go to step 16. If problem was not found, go to step 14.
Remove VSS. Inspect VSS and transmission for the following:
- Incorrect VSS.
- VSS damage.
- Excessive runout in final drive carrier assembly.
- Excessive VSS to speed sensor rotor gap.
- Incorrect speed sensor rotor alignment.
- Speed sensor rotor damage.
If problem was found, repair as necessary. See appropriate TRANSMISSION OVERHAUL article in AUTOMATIC TRANSMISSIONS. After repairs, go to step 16. If problem was not found, go to next step.
Replace VSS. After repairs, go to step 16.
Replace PCM. Program replacement PCM. See POWERTRAIN CONTROL MODULE under PROGRAMMING. After repairs, go to next step.
To verify repair, select DTC. Select CLEAR INFO. Drive vehicle. Ensure transmission VSS is more than 250 RPM for at least 2 seconds. Select SPECIFIC DTC. Enter DTC P0502. If test has run and passed, system is okay. If test did not rum and pass, go to step 2.