P0121

DTC P0121 Throttle/Pedal Position Sensor/Switch "A" Circuit Range/Performance Problem

HINT: This is the procedure for "throttle position sensor".

CIRCUIT DESCRIPTION

DTC Detecting Condition:

The throttle position sensor is mounted on the throttle body. It has 2 sensors to detect the throttle opening angle and a malfunction of the throttle position sensor.

The voltage applied to the terminals VTA1 and VTA2 of the ECM changes between 0 V to 5 V in proportion to the opening angle of the throttle valve. The VTA1 is a signal to indicate the actual throttle valve opening angle which is used for the engine control, and the VTA2 is a signal to indicate the information about the opening angle which is used for detecting a malfunction.

The ECM judges the current opening angle of the throttle valve from these signals input from terminals VTA1 and VTA2, and the ECM controls the throttle motor to make the throttle valve angle properly in response to the driving condition.

When a malfunction is detected, the throttle valve is locked at a certain opening angle. Also, the whole electronically controlled throttle operation is cancelled until the system returns to normal and the ignition switch is turned OFF.

MONITOR DESCRIPTION

Monitor Strategy:

Typical Enabling Conditions:

Typical Malfunction Thresholds:

The ECM uses throttle position sensor to monitor the throttle valve opening angle.

This sensor includes two signals, VTA1 and VTA2. VTA1 is used to detect the throttle opening angle and VTA2 is used to detect malfunctions in VTA1. There are several checks that the ECM confirms proper operation of the throttle position sensor and VTA1.

a. There is an expected specific voltage difference between VTA1 and VTA2 for each throttle opening angle.
b. VTA1 and VTA2 each have a specific voltage operating range.
c. VTA1 and VTA2 should never be close to the same voltage levels.

If the difference between VTA1 and VTA2 is incorrect (a), the ECM interprets this as a fault and will set a DTC. If VTA1 or VTA2 is out of the normal operating range (b), the ECM interprets this as a fault and will set a DTC. If VTA1 is within 0.02 V of VTA2 (c), the ECM interprets this as a short circuit in the throttle position sensor system and will set a DTC.

DTC P0121 relates to condition (a).

If the voltage output difference of the VTA1 and VTA2 deviates from the normal operating range, the ECM interprets this as a malfunction of the throttle position sensor. The ECM will turn on the MIL and a DTC is set.

INSPECTION PROCEDURE

HINT: Read freeze frame data using the hand-held tester or the OBD II scan tool. Freeze frame data records the engine conditions when a malfunction is detected. When troubleshooting, freeze frame data can help determine if the vehicle was running or stopped, if the engine was warmed up or not, if the air-fuel ratio was lean or rich, as well as other data from the time when a malfunction occurred.

REPLACE THROTTLE POSITION SENSOR