DTC P2121 Throttle / Pedal Position Sensor / Switch "D" Circuit Range / Performance: Description

WARNING: This page is about a different car, the 2007 Lexus GS 430. However, it is still accessible from the selected car via links, so may be relevant.

HINT:

The Electronic Throttle Control System (ETCS) does not use a throttle cable.
The accelerator pedal position sensor is a non-contact type.
The ETCS does not use a throttle cable.
The accelerator pedal position sensor is mounted on the accelerator pedal bracket and has 2 sensor circuits: VPA (main) and VPA2 (sub). This sensor uses Hall-effect elements to yield accurate signals, even in extreme driving conditions, such as at high speeds as well as very low speeds. The voltage, which is applied to terminals VPA and VPA2 of the ECM, varies between 0 V and 5 V in proportion to the operating angle of the accelerator pedal (throttle valve). A signal from VPA indicates the actual accelerator pedal opening angle (throttle valve opening angle) and is used for engine control. A signal from VPA2 conveys the status of the VPA circuit and is used to check the accelerator pedal position sensor itself.

The ECM monitors the actual accelerator pedal opening angle (throttle valve opening angle) through the signals from VPA and VPA2, and controls the throttle actuator according to these signals.

Fig 1: Accelerator Pedal Position Sensor Output Voltage Graph

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DTC DETECTION CONDITIONS CHART

DTC No.	DTC Detection Condition	Trouble Area
P2121	Difference between VPA and VPA2 is less than 0.4 V, or more than 1.2 V for 0.5 seconds (1 trip detection logic)	Accelerator position sensor ECM

HINT:

When any of these DTCs are set, check the accelerator pedal position sensor voltage by entering the following menus on the intelligent tester: DIAGNOSIS / ENHANCED OBD II/ DATA LIST / PRIMARY / ACCEL POS #1 and ACCEL POS #2.

TROUBLE AREAS CHART

Trouble Areas	ACCEL POS #1 When AP Released	ACCEL POS #2 When AP Released	ACCEL POS #1 When AP Depressed	ACCEL POS #2 When AP Depressed
VCP circuit open	0 to 0.2 V	0 to 0.2 V	0 to 0.2 V	0 to 0.2 V
Open or ground short in VPA circuit	0 to 0.2 V	1.2 to 2.0 V	0 to 0.2 V	3.4 to 5.0 V
Open or ground short in VPA2 circuit	0.5 to 1.1 V	0 to 0.2 V	2.6 to 4.5 V	0 to 0.2 V
EPA circuit open	4.5 to 5.0 V	4.5 to 5.0 V	4.5 to 5.0 V	4.5 to 5.0 V
Normal condition	0.5 to 1.1 V	1.2 to 2.0 V	2.6 to 4.5 V	3.4 to 5.0 V

HINT:

Accelerator pedal positions are expressed as voltages.
AP stands for Accelerator Pedal.