Monitor Description

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

This sensor including 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 performs confirm proper operation of the throttle position sensor and VTA1.

1. There is a specific voltage difference expected between VTA1 and VTA2 for each throttle opening angle.
2. VTA1 and VTA2 each have a specific voltage operating range.
3. 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) above.

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.