P0121

2AZ-FXE ENGINE CONTROL SYSTEM: SFI SYSTEM: P0121: Throttle / Pedal Position Sensor / Switch "A" Circuit Range / Performance Problem

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

CAUTION / NOTICE / HINT
HINT: This DTC relates to the Throttle Position (TP) sensor.

DESCRIPTION

The TP sensor is mounted on the throttle body, and detects the opening angle of the throttle valve. This sensor is a non-contact type. It uses Hall-effect elements in order to yield accurate signals even in extreme driving conditions, such as at high speeds as well as very low speeds.
The TP sensor has two sensor circuits which each transmits a signal, VTA1 and VTA2. VTA1 is used to detect the throttle valve angle and VTA2 is used to detect malfunctions in VTA1. The sensor signal voltages vary between 0 V and 5 V in proportion to the throttle valve opening angle, and are transmitted to the VTA terminals of the ECM (included in the hybrid vehicle control ECU).
As the valve closes, the sensor output voltage decreases and as the valve opens, the sensor output voltage increases. The ECM calculates the throttle valve opening angle according to these signals and controls the throttle actuator in response to driver inputs. These signals are also used in calculations such as air-fuel ratio correction, power increase correction and fuel-cut control.





HINT:
- When any of these DTCs are set, check the throttle valve opening angle by selecting the following menu items on the Techstream: Powertrain / Engine / Data List / ETCS / Throttle Position No. 1 and Throttle Position No. 2.
- Throttle Position No. 1 denotes the VTA signal, and Throttle Position No. 2 denotes the VTA2 signal.

Reference (Normal Condition):










MONITOR DESCRIPTION

The ECM (included in the hybrid vehicle control ECU) uses the TP 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 (included in the hybrid vehicle control ECU) performs several checks to confirm proper operation of the TP 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 range, the ECM interprets this as a malfunction of the TP 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.

MONITOR STRATEGY





TYPICAL ENABLING CONDITIONS





TYPICAL MALFUNCTION THRESHOLDS





FAIL-SAFE

When this DTC, as well as other DTCs relating to ETCS (Electronic Throttle Control System) malfunctions, is set, the ECM (included in the hybrid vehicle control ECU) 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 6.5° 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 gently, the vehicle can be driven slowly.
Fail-safe mode continues until a pass condition is detected, and the power switch is then turned off.

INSPECTION PROCEDURE
HINT: Read freeze frame data using the Techstream. The ECM (included in the hybrid vehicle control ECU) records vehicle and driving condition information as freeze frame data the moment a DTC is stored. 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 DTCS OUTPUT (IN ADDITION TO DTC P0121)
(a) Connect the Techstream to the DLC3.
(b) Turn the power switch on (IG).
(c) Turn the tester on.
(d) Select the following menu items: Powertrain / Engine / Trouble Code.
(e) Read the DTCs.
Result:






B -- GO TO DTC CHART
A -- REPLACE THROTTLE BODY ASSEMBLY