LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Toyota >> 2009 >> Prius Base >> Repair and Diagnosis (Single Page) >> Engine Performance >> Testing & Diagnosis >> Engine Control System >> SFI System >> DTC P0121 Throttle / Pedal Position Sensor / Switch "A" Circuit Range / Performance Problem >> Monitor Description
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Monitor Description

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

This sensor has 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.

There is a specific voltage difference between VTA1 and VTA2 for each throttle opening angle.

If VTA1 or VTA2 is out of the normal operating range, the ECM interprets this as a fault and will set a DTC.

If VTA1 is within 0.02 V of VTA2, the ECM interprets this as a short circuit in the throttle position sensor system and will set a DTC.

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