3Gr-Fe Engine Control System. Dtc P0120 Throttle Pedal Position Sensor / Switch A Circuit Malfunction

The Throttle Position (TP) sensor is mounted on the throttle body, and detects the opening angle of the throttle valve. This sensor is a non-contact type, and 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.

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.

Lexus Gs430, Gs300. Uzs190 Grs190.3Gr-Fe Engine Control System.Sfi System.
Dtc
P0120 Throttle Pedal Position Sensor / Switch A Circuit Malfunction

DTC No.	DTC Detection Condition	Trouble Area
P0120	Output voltage of VTA1 quickly fluctuates beyond lower and upper malfunction thresholds for 2 seconds (1 trip detection logic)	Throttle Position (TP) sensor (built into throttle body) ECM
P0122	Output voltage of VTA1 0.2 V or less for 2 seconds (1 trip detection logic)	TP sensor (built into throttle body) Short in VTA1 circuit Open in VC circuit ECM
P0123	Output voltage of VTA1 4.8 V or more for 2 seconds (1 trip detection logic)	TP sensor (built into throttle body) Open in VTA1 circuit Open in E2 circuit Short between VC and VTA1 circuits ECM
P0220	Output voltage of VTA2 quickly fluctuates beyond lower and upper malfunction thresholds for 2 seconds (1 trip detection logic)	TP sensor (built into throttle body) ECM
P0222	Output voltage of VTA2 0.5 V or less for 2 seconds (1 trip detection logic)	TP sensor (built into throttle body) Short in VTA2 circuit Open in VC circuit ECM
P0223	Output voltage of VTA2 4.8 V or more, and VTA1 between 0.2 V and 1.8 V, for 2 seconds (1 trip detection logic)	TP sensor (built into throttle body) Open in VTA2 circuit Open in E2 circuit Short between VC and VTA2 circuits ECM
P2135	Either condition (a) or (b) met (1 trip detection logic): (a) Difference between output voltages of VTA1 and VTA2 0.02 V or less for 0.5 seconds or more (b) Output voltage of VTA1 0.2 V or less, and VTA2 0.5 V or less, for 0.4 seconds or more	Short between VTA1 and VTA2 circuits TP sensor (built into throttle body) ECM

HINT:

When any of these DTCs are set, check the throttle valve opening angle by entering the following menus on an intelligent tester: Powertrain / Engine / Data List / Throttle Sensor Position and Throttle Position No. 2.

Throttle Sensor Position denotes the VTA1 signal (expressed in percentages), and Throttle Position No. 2 denotes the VTA2 signal (expressed in voltages).

Reference (Normal Condition):

Tester Display
Accelerator Pedal Fully Released
Accelerator Pedal Fully Depressed
Throttle Sensor Position
10 to 24 %
64 to 96 %
Throttle Position No. 2
2.1 to 3.1 V
4.5 to 5.0 V

MONITOR DESCRIPTION

The ECM uses the Throttle Position (TP) sensor to monitor the throttle valve opening angle. There are several checks that the ECM performs to confirm the proper operation of the TP sensor.

A specific voltage difference is expected between the sensor terminals, VTA1 and VTA2, for each throttle valve opening angle. If the difference between VTA1 and VTA2 is incorrect, the ECM interprets this as a malfunction in the sensor, and sets a DTC.

VTA1 and VTA2 each have a specific voltage range. If VTA1 or VTA2 is outside the normal operating range, the ECM interprets this as a malfunction in the sensor, and sets a DTC.

VTA1 and VTA2 should never be close to the same voltage level. If VTA1 is within 0.02 V of VTA2, the ECM determines that there is a short circuit in the sensor, and sets a DTC.

FAIL-SAFE

When any of these DTCs, as well as other DTCs relating to ETCS (Electronic Throttle Control System) malfunctions, are set, the ECM enters fail-safe mode. During the ECM cuts the current to the throttle actuator off, and the throttle valve is returned to a 6° 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.

WIRING DIAGRAM

INSPECTION PROCEDURE

HINT:

If other DTCs relating to different systems that have terminal E2 as the ground terminal are output simultaneously, terminal E2 may have an open circuit.

Read freeze frame data using the intelligent tester. Freeze frame data records the engine conditions 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.

These DTCs relate to the Throttle Position (TP) sensor.

1.READ VALUE USING INTELLIGENT TESTER (THROTTLE POSITION SENSOR AND THROTTLE POSITION NO. 2)

Connect the intelligent tester to the DLC3.

Turn the engine switch on (IG) and turn the intelligent tester ON.

Enter the following menus: Powertrain / Engine / Data List / Throttle Sensor Position and Throttle Position No. 2.

Check the values displayed on the tester.

Result:

TP#1 (VTA1) When AP Released	TP#2 (VTA2) When AP Released	TP#1 (VTA1) When AP Depressed	TP#2 (VTA2) When AP Depressed	Trouble Area	Proceed to
0 %	Between 0 V and 0.2 V	0 %	Between 0 V and 0.2 V	VC circuit open	A
100 %	Between 4.5 V and 5.0 V	100 %	Between 4.5 V and 5.0 V	E2 circuit open	A
0 % or 100 %	Between 2.1 V and 3.1 V (Fail-safe)	0 % or 100 %	Between 2.1 V and 3.1 V (Fail-safe)	VTA1 circuit open or ground short	A
Approx 19 % (Fail-safe)	Between 0 V and 0.2 V, or 4.5 V and 5.0 V	Between 10 % and 24 % (Fail-safe)	Between 0 V and 0.2 V, or 4.5 V and 5.0 V	VTA2 circuit open or ground short	A
Between 10 % and 24 %	Between 2.1 V and 3.1 V	Between 64 % and 96 % (Not fail-safe)	Between 4.5 V and 5.0 V (Not fail-safe)	TP sensor circuit normal	B

HINT:

TP#1 denotes Throttle Sensor Position, and TP#2 denotes Throttle Position No. 2.

AP denotes Accelerator Pedal.

VTA1 is expressed as percentages, and VTA2 is expressed as voltages.

Go to step 5

A

2.CHECK HARNESS AND CONNECTOR (THROTTLE POSITION SENSOR - ECM)

Disconnect the E39 throttle body connector.

Disconnect the E6 and E8 ECM connectors.

Measure the resistance.

Standard resistance (Check for open):

Tester Connection	Specified Condition
VC (E39-5) - VC2 (E6-29)	Below 1 Ω
VTA (E39-6) - VTA1 (E8-23)	Below 1 Ω
VTA2 (E39-4) - VTA2 (E8-22)	Below 1 Ω
E2 (E39-3) - E3 (E6-30)	Below 1 Ω

Standard resistance (Check for short):

Tester Connection	Specified Condition
VC (E39-5) or VC2 (E6-29) - Body ground	10 kΩ or higher
VTA (E39-6) or VTA1 (E8-23) - Body ground	10 kΩ or higher
VTA2 (E39-4) or VTA2 (E8-22) - Body ground	10 kΩ or higher

Reconnect the throttle body connector.

Reconnect the ECM connector.

REPAIR OR REPLACE HARNESS AND CONNECTOR

OK

3.INSPECT ECM (VC VOLTAGE)

Disconnect the E39 throttle body connector.

Turn the engine switch on (IG).

Measure the voltage between the terminals of the E6 ECM connector.
Standard voltage:
Tester Connection
Specified Condition
VC2 (E6-29) - E3 (E6-30)
4.5 to 5.0 V

Reconnect the throttle body connector.

REPLACE ECM

OK

4.REPLACE THROTTLE BODY

NEXT

5.CHECK WHETHER DTC OUTPUT RECURS (THROTTLE POSITION SENSOR DTCS)

Connect the intelligent tester to the DLC3.

Turn the engine switch on (IG) and turn the tester ON.

Clear DTCs (Click here).

Start the engine.

Allow the engine to idle for 15 seconds or more.

Enter the following menus: Powertrain / Engine / DTC.

Read DTCs.

Result:

Display (DTC Output)
Proceed to
P0120, P0122, P0123, P0220, P0223, and/or P2135
A
No output
B

SYSTEM OK

REPLACE ECM

Tester Display	Accelerator Pedal Fully Released	Accelerator Pedal Fully Depressed
Throttle Sensor Position	10 to 24 %	64 to 96 %
Throttle Position No. 2	2.1 to 3.1 V	4.5 to 5.0 V

Tester Connection	Specified Condition
VC2 (E6-29) - E3 (E6-30)	4.5 to 5.0 V

Display (DTC Output)	Proceed to
P0120, P0122, P0123, P0220, P0223, and/or P2135	A
No output	B