| CAUTION | If ECM replacement is instructed in following testing, always ensure ECM harness connector and ground circuit are okay. If either are suspect, repair and repeat testing to confirm ECM malfunction. If ECM is replaced, ECM must be programmed with proper ignition key code for engine immobilizer system. For programming procedures, see COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION. |
Circuit Description
The Throttle Position (TP) sensor is a 2 variable resistor sensor that monitors throttle opening and TP sensor malfunction. Based on TP sensor signal, ECM determines vehicle driving condition and uses throttle control motor to set throttle angle accordingly. If DTC P0120 is set, ECM shuts down power to throttle control motor and electromagnetic clutch.
DTC P0120 is set when ECM consistently detects .2 volt or less, or 4.8 volts or more from VTA circuit, or .5 volt or less from VTA2 circuit for 2 seconds. DTC P0120 is also set when ECM consistently detects .2 volt or more and 2.0 volts or less from VTA circuit, and 4.97 volts or more from VTA2 circuit for 2 seconds.
DTC P0120 is also set when ECM consistently detects .02 volt or less from VTA and VTA2 circuit for 2 seconds. DTC P0120 is also set when ECM consistently detects .2 volt or less from VTA circuit and .5 volt or less from VTA2 circuit for .4 second. Possible causes are
- Open or short in TP sensor circuit.
- Faulty TP sensor.
- Faulty ECM.
Diagnostic Aids
After confirming DTC P0120, use scan tool to access CURRENT DATA to confirm throttle valve opening percentage with throttle open and closed. If percentage displayed on scan tool is always zero percent, VC circuit may be open. Using scan tool, read freeze frame data. Freeze frame records engine conditions when malfunction is detected.