Note. For component location, see appropriate illustration in THEORY & OPERATION article.
Circuit Description
TP sensor is a variable resistor mounted to throttle body and detects throttle opening angle. ECM determines vehicle driving condition and adjusts air/fuel mixture accordingly. DTC is set after vehicle speed has exceeded 19 MPH once and TP sensor output voltage is out of range while vehicle speed is 0-19 MPH. Possible cause is
- Defective Throttle Position (TP) sensor.
Diagnostic Aids
After confirming DTC P0121, 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 or VTA circuit may be shorted. If percentage displayed on scan tool is always 75 percent, check for open in E2 circuit. Using scan tool, read freeze frame data. Freeze frame records engine conditions when malfunction is detected.