Circuit Description

WARNING: This page is about a different car, the 2003 Lexus ES 300. However, it is still accessible from the selected car via links, so may be relevant.

Park/neutral position switch goes on when shift lever is in "N" or "P" shift position. When it goes on, terminal NSW of ECM is grounded to body ground via starter relay, and terminal NSW voltage becomes zero volts. When shift lever is in "D", "2", "L" or "R" position, park/neutral position switch goes off, as does voltage of ECM. Terminal NSW becomes battery voltage and voltage of ECM internal power source. If shift lever is moved from "N" position to "D" position, this signal is used for air-fuel ratio correction and for idle speed control (estimated control), etc. If P0705 is set, 2 or more switches are on simultaneously for "N", "2", "L" and "R" positions (2 trip detection logic). If P0850 is set, vehicle speed is 43 mph or more, engine speed is 1500-2500 RPM, and park/neutral position switch is on ("N" position) for more than 30 seconds (2 trip detection logic). Possible causes are:

Short in park/neutral position switch assembly circuit.
Faulty park/neutral position switch assembly.
Faulty ECM.