Description

DATA TROUBLE CODE: P0120

SYSTEM: Throttle Position Circuit Malfunction





CIRCUIT DESCRIPTION
The Throttle Position Sensor is mounted in the Throttle Body and detects the throttle valve opening angle. When the throttle valve is fully closed, the IDL contacts in the Throttle Position Sensor are on, so the voltage at the terminal IDL of the Engine Control Module becomes 0 volts. At this time, a voltage of approximately 0.7 volts is applied to terminal VTA of the Engine Control Module. When the throttle valve is opened, the IDL contacts go off and thus the power source voltage of approximately 12 volts in the Engine Control Module is applied to the terminal IDL of the Engine Control Module. The voltage applied to the terminal VTA of the Engine Control Module increases in proportion to the opening angle of the throttle valve and becomes approximately 3.5 - 5.0 volts when the throttle valve is fully opened. The Engine Control Module judges the vehicle driving conditions from these signals input from terminals VTA and IDL, and uses them as one of the conditions for deciding the air-fuel ratio correction, power increases correction and fuel-cut control etc.


DIAGNOSTIC TROUBLE CODE DETECTING CONDITION
- VTA voltage is less than 0.1 volt and closed throttle position switch is OFF.
- VTA voltage is greater than 4.9 volts.

TROUBLE AREA
- Open or short in Throttle Position Sensor circuit.
- Throttle Position Sensor.
- Engine Control Module.

NOTE: If there is open circuit in IDL line, Diagnostic Trouble Code P0120 does not indicate. After confirming Diagnostic Trouble Code P0120 use the OBDII scan tool or LEXUS hand-held tester to confirm the throttle valve opening percentage and closed throttle position switch condition.

If OBDII scan tool or LEXUS hand-held tester reads 0% when checked with throttle fully closed AND fully open; trouble areas could be VC line open and/or VTA line open or short.
If OBDII scan tool or LEXUS hand-held tester reads approximately 99% when checked with throttle fully closed AND approximately 100% when checked with throttle fully open; trouble area could be E2 line open.