Diagnosis & Repair

If using Lexus scan tool, go to next step. If not using Lexus scan tool, go to step 3.
Connect Lexus scan tool to DLC No. 3. See Figure. Turn ignition on. Turn scan tool on. Using scan tool, read transaxle shift positions while shifting transaxle shift lever through all gear positions. If scan tool display does not indicate correct shifter positions, go to next step. If scan tool display indicates correct shifter positions, Park/Neutral Position (PNP) switch is functioning properly. Problem is internal transaxle. Identify symptom and repair as necessary. See appropriate article in AUTOMATIC TRANSMISSIONS.
Access ECM behind glove box. Turn ignition on. Backprobing, measure voltage between ground and ECM E8 connector NSW circuit terminal No. 20 (Black/White wire). Also measure voltage between ground and ECM E9 connector "R" circuit terminal No. 8 (Red/Black wire), "2" circuit terminal No. 14 (Blue/White wire), and "L" circuit terminal No. 13 (Yellow wire). See Figure. Shift lever through all gear positions. See Fig 1. If voltage is not as specified, go to next step. If voltage is as specified, PNP switch is functioning properly. Problem is internal transaxle. Identify symptom and repair as necessary. See appropriate article in AUTOMATIC TRANSMISSIONS.
Check PNP switch. See ENGINE SENSORS & SWITCHES in appropriate SYSTEM & COMPONENT TESTING article. Replace PNP switch as necessary. If PNP switch is okay, check for short circuit in wiring harness between battery and PNP switch. Also check wiring harness between ECM and PNP switch. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary and retest system. If wiring harness is okay, replace ECM and retest system.

Fig 1: Testing Park/Neutral Position Switch Circuits