Lexus RX300 (MCU15). Manual - part 201

P24296

Throttle Position
Sensor

Engine ECU

VC

VTA

E2

DI–36

–

DIAGNOSTICS

ENGINE

LEXUS RX300   (RM785E)

DTC

P0120

Throttle Position Sensor Circuit Malfunction

CIRCUIT DESCRIPTION

The throttle position sensor is mounted in the throttle body and
detects the throttle valve opening angle. When the throttle valve
is fully closed, a voltage of approx. 0.7 V is applied to terminal
VTA of the engine ECU. The voltage applied to the terminals
VTA of the engine ECU increases in proportion to the opening
angle of the throttle valve and becomes approx. 2.7 – 5.2 when
the throttle valve is fully opened. The engine ECU judges the
vehicle driving conditions from these signals input from termi-
nals VTA and uses them as one of the conditions for deciding
the air–fuel ratio correction, power increase correction and
fuel–cut control etc.

DTC No.

DTC Detecting Condition

Trouble Area

P0120

Condition (a) or (b) continues:

(a) VTA < 0.1 V

(b) VTA > 4.9 V

S Open or short in throttle position sensor circuit

S Throttle position sensor

S Engine ECU

HINT:
After confirming DTC P0120, use the hand–held tester to confirm the throttle valve opening percentage and
closed throttle position switch condition.

Throttle valve opening position

expressed as percentage

Trouble Area

Throttle valve fully closed

Throttle valve fully open

Trouble Area

0 %

0%

VC line open

VTA line open or short

Approx. 100%

Approx. 100%

E2 line open

DI84A–01

S05019

Throttle Position Sensor

Engine ECU

1

3

2

BR

L–W

Y–B

2

E7

E7

23

18

E7

E2

VTA1

VC

5 V

T11

FI7052

–

DIAGNOSTICS

ENGINE

DI–37

LEXUS RX300   (RM785E)

WIRING DIAGRAM

INSPECTION PROCEDURE

HINT:

S

If DTCs P0110, P0115 and P0120 are output simultaneously, E2 (sensor ground) may be open.

S

Read freeze frame data using hand–held tester. Because freeze frame records the engine conditions
when the malfunction is detected. When troubleshooting it is useful for determining whether the vehicle
was running or stopped, the engine was warmed up or not, the air–fuel ratio was lean or rich, etc. at
the time of the malfunction.

When using hand–held tester:

1

Connect hand–held tester, read throttle valve opening percentage.

PREPARATION:
(a)

Connect the hand–held tester to the DLC3.

(b)

Turn the ignition switch ON and push the hand–held tes-
ter main switch ON.

CHECK:
Read the throttle valve opening percentage.
OK:

Throttle valve

Throttle valve opening position ex-

pressed as percentage

Fully open

Approx. 75 %

Fully closed

Approx. 10 %

A00437

ON

1 (+)

S05339

1

2

3

DI–38

–

DIAGNOSTICS

ENGINE

LEXUS RX300   (RM785E)

OK

Check for intermittent problems (See page
DI–3).

NG

2

Check voltage between terminal 1 of wire harness side connector and body
ground.

PREPARATION:
(a)

Remove the engine ECU with connector still connected
(See page FI–70).

(b)

Turn the ignition switch ON.

CHECK:
Measure voltage between terminal 1 (VC) of wire harness side
connector and body ground.
OK:

Voltage: 4.5 – 5.5 V

NG

Go to step 5.

OK

3

Check throttle position sensor.

PREPARATION:
Disconnect the throttle position sensor connector.
CHECK:
Measure voltage between terminals 1, 3 and 2 of throttle posi-
tion sensor.
OK:

Terminals

Throttle valve

Resistance

1 – 2

–

2.5 – 5.9 kΩ

3 – 2

Fully closed

0.2 – 6.3 kΩ

3 – 2

Fully open

2.0 – 10.2 kΩ

OK

Replace throttle position sensor.

NG

A02021

ON

VTA1 (+) E2 (–)

A02022

ON

E2 (–)

VC (+)

–

DIAGNOSTICS

ENGINE

DI–39

LEXUS RX300   (RM785E)

4

Check voltage between terminals VTA1 and E2 of engine ECU.

PREPARATION:
(a)

Remove the engine ECU with connector still connected
(See page FI–70).

(b)

Turn the ignition switch ON.

CHECK:
Measure voltage between terminals VTA1 and E2 of the engine
ECU connector.
OK:

Throttle valve

Voltage

Fully closed

0.3 – 1.0 V

Fully open

2.7 – 5.2 V

NG

Check and replace engine ECU (See page
IN–32).

OK

Check for open and short circuit in harness and connector between engine ECU and throttle posi-
tion sensor (VTA line) (See page IN–32).

5

Check voltage between terminals VC and E2 of engine ECU.

PREPARATION:
(a)

Remove the engine ECU with connector still connected
(See page FI–70).

(b)

Turn the ignition switch ON.

CHECK:
Measure voltage between terminals VC and E2 of the engine
ECU connector.
OK:

Voltage: 4.5 – 5.5 V

NG

Check and replace engine ECU (See page
IN–32).

OK

Check for open in harness and connector be-
tween engine ECU and sensor (VC line) (See
page IN–32).