P0121

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

DESCRIPTION

DTC Detection Conditions:

HINT:
- This Electronic Throttle Control System (ETCS) does not use a throttle cable.
- This throttle position sensor is a non-contact type.

The throttle position sensor is mounted on the throttle body and it detects the opening angle of the throttle valve. This sensor is electronically controlled and uses Hall-effect elements so that accurate control and reliability can be obtained. The throttle position sensor has 2 sensor elements VTA and VTA2, each with their own signal outputs. VTA is used to detect the throttle opening angle and VTA2 is used to detect malfunctions in VTA. Voltage applied to VTA and VTA2 changes between 0 V to 5 V in proportion to the opening angle of the throttle valve. There are several checks that the ECM performs to confirm proper operation of the throttle position sensor.

The ECM judges the current opening angle of the throttle valve from these signals input from terminals VTA and VTA2, and the ECM controls the throttle actuator to set the throttle valve angle properly in response to driver inputs.

MONITOR DESCRIPTION

Monitor Strategy:

Typical Enabling Conditions:

Typical Malfunctions Thresholds:

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

This sensor includes 2 signals: VTA and VTA2. VTA is used to detect the throttle opening angle and VTA2 is used to detect malfunctions in VTA. There are several checks that the ECM performs to confirm proper operation of the throttle position sensor and VTA.

There is a specific voltage difference expected between VTA and VTA2 for each throttle opening angle. If the output voltage difference of the VTA and VTA2 deviates from the normal operating range, the ECM interprets this as a malfunction of the throttle position sensor. The ECM will illuminate the MIL and set a DTC. This monitor runs for 2 seconds (the first 2 seconds of engine idle) after the engine is started (1 trip detection logic).

FAIL-SAFE

If the ETCS has a malfunction, the ECM cuts off current to the throttle actuator. The throttle valve returns to a predetermined opening angle (approximately 16 degrees) by the force of the return spring. The ECM then adjusts the engine output by controlling the fuel injection (intermittent fuel-cut) and ignition timing in accordance with the accelerator pedal opening angle to enable the vehicle to continue at a minimal speed.
If the accelerator pedal is depressed firmly and slowly, the vehicle can be driven slowly.
If a "pass" condition is detected and then the engine switch is turned off, the fail-safe operation will stop and the system will return to normal.

Wiring Diagram:

Step 1:

INSPECTION PROCEDURE

HINT:
- Read freeze frame data using the intelligent tester. 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, and other data from the time the malfunction occurred.
- This is the repair procedure of the throttle position sensor.