SFI SYSTEM, Diagnostic DTC:P0121

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

DESCRIPTION

Refer to DTC P0120 Click here.

Tech Tips

This DTC relates to the throttle position sensor.

DTC No. DTC Detection Condition Trouble Area
P0121 Difference between VTA and VTA2 voltages less than 0.8 V, or more than 1.6 V for 2 seconds (1 trip detection logic) Throttle position sensor (built into throttle body)

MONITOR DESCRIPTION

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

This sensor transmits two signals: VTA and VTA2. VTA is used to detect the throttle opening angle and VTA2 is used to detect malfunctions in VTA. The ECM performs several checks to confirm the proper operation of the throttle position sensor and VTA.

For each throttle opening angle, a specific voltage difference is expected between the outputs of VTA and VTA2. If the output voltage difference between the two signals deviates from the normal operating range, the ECM interprets this as a malfunction of the throttle position sensor. The ECM illuminates the MIL and sets the DTC.

If the malfunction is not repaired successfully, the DTC is set 2 seconds after the engine is next started.

FAIL-SAFE

When this DTC, as well as other DTCs relating to electronic throttle control system malfunctions, is set, the ECM enters fail-safe mode. During fail-safe mode, the ECM cuts the current to the throttle actuator off, and the throttle valve is returned to a 7° throttle angle by 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 allow the vehicle to continue at a minimal speed. If the accelerator pedal is depressed firmly and gently, the vehicle can be driven slowly.

Fail-safe mode continues until a pass condition is detected, and the engine switch is then turned off.

INSPECTION PROCEDURE

Tech Tips

Read freeze frame data using the intelligent tester. Freeze frame data records the engine condition when malfunctions are detected. When troubleshooting, freeze frame data can help determine if the vehicle was moving or stationary, 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.

PROCEDURE


  1. CHECK ANY OTHER DTC OUTPUT (IN ADDITION TO DTC P0121)


    1. Connect the intelligent tester to the DLC3.

    2. Turn the engine switch on (IG).

    3. Turn the tester ON.

    4. Enter the following menus: Powertrain / Engine / DTC.

    5. Read the DTCs.

      Result
      Result Proceed to
      DTC P0121 is output A
      DTC P0121 and other DTCs are output B

      Tech Tips

      If any DTCs other than P0121 are output, troubleshoot those DTCs first.


    B

    GO TO DTC CHART Click here

    A

    REPLACE THROTTLE BODY Click here