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

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.

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

DTC No.	DTC Detection Condition	Trouble Area
P0120	VTA is 0.2 V or less or VTA is 4.8 V or more (for 2 seconds) (1 trip detection logic)	Throttle position sensor (built into throttle body) ECM
P0122	VTA is 0.2 V or less (for 2 seconds) (1 trip detection logic)	Throttle position sensor (built into throttle body) Short in VTA circuit Open in VC circuit ECM
P0123	VTA is 4.8 V or more (for 2 seconds) (1 trip detection logic)	Throttle position sensor (built into throttle body) Open in VTA circuit Open in E2 circuit VC and VTA circuit are shorted ECM
P0220	VTA2 is 0.5 V or less, or VTA2 is 4.8 V or more VTA is 0.2 V or more, and VTA is 1.8 V or less (1 trip detection logic)	Throttle position sensor (built into throttle body) ECM
P0222	VTA2 is 0.5 V or less (for 2 seconds) (1 trip detection logic)	Throttle position sensor (built into throttle body) Short in VTA2 circuit Open in VC circuit ECM
P0223	VTA2 is 4.8 V or more when VTA is between 0.2 to 1.8 V (for 2 seconds) (1 trip detection logic)	Throttle position sensor (built into throttle body) Open in VTA2 circuit Open in E2 circuit VC and VTA2 circuit are shorted ECM
P2135	Condition (a) continues for 0.5 seconds or more, or condition (b) continues for 0.4 seconds or more: (a) Difference between VTA and VTA2 is 0.02 V or less (b) VTA is 0.2 V or less, and VTA2 is 0.5 V or less (1 trip detection logic)	VTA and VTA2 circuit are shorted Throttle position sensor (built into throttle body) ECM

HINT:

After confirming DTCs, use the intelligent tester to confirm the throttle valve opening percentage and throttle position sensor condition.
Throttle Position is the VTA signal. Throttle Position No. 2 is the VTA2 signal.

Reference (Normal condition):
Tester Display	Accelerator Pedal Fully Released	Accelerator Pedal Fully Depressed
Throttle 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 sensor to monitor the throttle valve opening angle.

There is a specific voltage difference expected between VTA and VTA2 for each throttle opening angle.
If the difference between VTA and VTA2 is incorrect, the ECM interprets this as a fault and will set a DTC.
VTA and VTA2 each have a specific voltage operating range.
If VTA or VTA2 is out of the normal operating range, the ECM interprets this as a fault and will set a DTC.
VTA and VTA2 should never be close to the same voltage levels.
If VTA is within 0.02 V of VTA2, the ECM interprets this as a short circuit in the throttle position sensor system and will 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°) 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

INSPECTION PROCEDURE

HINT:

If DTCs related 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 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.

1.READ DATA LIST (THROTTLE POSITION SENSOR VALUE)

Connect the intelligent tester to the DLC3.

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

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

Read the value.

Result:

Throttle position expressed as percentage and voltage				Trouble Area	Proceed to
Accelerator pedal released		Accelerator pedal depressed
Throttle Position (VTA)	Throttle Position No. 2 (VTA2)	Throttle Position (VTA)	Throttle Position No. 2 (VTA2)
0%	0 to 0.2 V	0%	0 to 0.2 V	VC circuit open	A
100%	4.5 to 5.0 V	100%	4.5 to 5.0 V	E2 circuit open	A
0% or 100%	2.1 to 3.1 V (fail-safe)	0% or 100%	2.1 to 3.1 V (fail-safe)	VTA circuit open or ground short	A
Approx. 16% (fail-safe)	0 to 0.2 or 4.5 to 5.0 V	Approx. 16% (fail-safe)	0 to 0.2 or 4.5 to 5.0 V	VTA2 circuit open or ground short	A
10 to 24%	2.1 to 3.1 V	64 to 96% (no fail-safe)	4.5 to 5.0 V (no fail-safe)	Throttle positon sensor circuit is normal	B

Go to step 5

A

2.CHECK WIRE HARNESS (THROTTLE POSITION SENSOR - ECM)

Disconnect the E39 throttle actuator connector.

Disconnect the E8 ECM connector.

Measure the resistance of the wire harness side connectors.

Standard resistance:

Tester Connection	Specified Condition
E39-5 (VC) - E8-29 (VC)	Below 1 Ω
E39-6 (VTA) - E8-23 (VTA)	Below 1 Ω
E39-4 (VTA2) - E8-22 (VTA2)	Below 1 Ω
E39-3 (E2) - E8-28 (E2)	Below 1 Ω
E39-5 (VC) or E8-29 (VC) - Body ground	10 kΩ or higher
E39-6 (VTA) or E8-23 (VTA) - Body ground	10 kΩ or higher
E39-4 (VTA2) or E8-22 (VTA2) - Body ground	10 kΩ or higher
E39-3 (E2) or E8-28 (E2) - Body ground	10 kΩ or higher

REPAIR OR REPLACE HARNESS AND CONNECTOR

OK

3.CHECK ECM (VC VOLTAGE)

Turn the engine switch on (IG).

Measure the voltage of the ECM.
Standard voltage:
Tester Connection
Specified Condition
E8-29 (VC) - E8-28 (E2)
4.5 to 5.5 V

REPLACE ECM

OK

4.REPLACE THROTTLE BODY

NEXT

5.READ OUTPUT DTC (THROTTLE POSITION SENSOR DTCS ARE OUTPUT AGAIN)

Clear the DTC.

Start the engine and allow the engine to idle for 15 seconds or more.

Read the DTC.

Result:

Display (DTC output)
Proceed to
P0120, P0122, P0123, P0220, P0222, P0223 or P2135
A
No output
B

SYSTEM OK

REPLACE ECM

Tester Connection	Specified Condition
E8-29 (VC) - E8-28 (E2)	4.5 to 5.5 V

Display (DTC output)	Proceed to
P0120, P0122, P0123, P0220, P0222, P0223 or P2135	A
No output	B