Lexus ES300 (1997 year). Manual - part 316

A00437

1(+)

ON

BE6653
S05338

S05339

1

2

3

DI–40

–

DIAGNOSTICS

ENGINE

192

1997 LEXUS ES300   (RM511U)

2

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

PREPARATION:
(a)

Disconnect the throttle position sensor connector.

(b)

Turn 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 
position sensor.
OK:

Terminals

Throttle valve

Resistance

1  

∼

  2



2.5  

∼

  5.9 k

Ω

3

2

Fully closed

0.2  

∼

  6.3 k

Ω

3  

∼

  2

Fully open

2.0  

∼

  10.2 k

Ω

NG

 Replace throttle position sensor.

OK

A00218

ON

E2(–)

VTA1(+)

BE6653
P24315

A00219

ON

E2(–)

VC(+)

BE6653
P24316

–

DIAGNOSTICS

ENGINE

DI–41

193

1997 LEXUS ES300   (RM511U)

4

Check voltage between terminals VTA1 and E2 of ECM.

PREPARATION:
(a)

Remove the glove compartment (See page 

SF–64

).

(b)

Turn ignition switch ON.

CHECK:
Measure voltage between terminals VTA1 and E2 of ECM con-
nector.
OK:

Throttle valve

Voltage

Fully closed

0.3 

∼

 1.0 V

Fully open

2.7 

∼

 5.2 V

NG

Check for open and short in harness and
connector between ECM and throttle position
sensor (VTA line) (See page 

IN–27

).

OK

Check and replace ECM (See page 

IN–27

).

5

Check voltage between terminals VC and E2 of ECM.

PREPARATION:
(a)

Remove the glove compartment (See page 

SF–64

).

(b)

Turn ignition switch ON.

CHECK:
Measure voltage between terminals VC and E2 of ECM con-
nector.
OK:

Voltage:  4.5 

∼

 5.5 V

NG

 Check and replace ECM (See page 

IN–27

).

OK

Check for open in harness and connector 
between ECM and sensor (VC line)
(See page 

IN–27

).

DI–42

–

DIAGNOSTICS

ENGINE

194

1997 LEXUS ES300   (RM511U)

DTC

P0121

Throttle/Pedal Position Sensor/Switch ”A”
Circuit Range/Performance Problem

CIRCUIT DESCRIPTION

Refer to DTC P0120 (Throttle/Pedal Position Sensor/Switch "A" Circuit Malfunction) on page 

DI–38

.

DTC No.

DTC Detecting Condition

Trouble Area

P0121

 After the vehicle speed has been exceeded 30 km/h (19 mph)

even once, the output value of the throttle position sensor is

out of the applicable range while the vehicle speed between 30

km/h (19 mph) and 0 km/h (0 mph)

Throttle position sensor

INSPECTION PROCEDURE

1

Are there any other codes (besides DTC P0121) being output?

YES

 Go to relevant DTC chart. 

NO

Replace throttle position sensor.

DI09H–01

P21242 FI7210

A00027

Atomosphere

Cover

Ideal Air–Fuel Mixture

Air Fuel Ratio

Richer

Leaner

Exhaust Gas

Flange
Platinum Electrode
Solid Electrolyte

(Zirconia Element)

Platium Electrode

Heater

Coating(Ceramic)

Output V

oltage

–

DIAGNOSTICS

ENGINE

DI–43

195

1997 LEXUS ES300   (RM511U)

DTC

P0125

Insufficient  Coolant Temp. for Closed Loop
Fuel Control

CIRCUIT DESCRIPTION

To obtain a high purification rate for the CO, HC and NOx components of the exhaust gas, a three–way
catalytic converter is used, but for the most efficient use of the three–way catalytic converter, the air–fuel
ratio must be precisely controlled so that it is always close to the stoichiometric air–fuel ratio.
The oxygen sensor has the characteristic whereby its output voltage changes suddenly in the vicinity of the
stoichiometric air–fuel ratio. This characteristic is used to detect the oxygen concentration in the exhaust
gas and provide feedback to the computer for control of the air–fuel ratio.
When the air–fuel ratio becomes LEAN, the oxygen concentration in the exhaust increases and the oxygen
sensor informs the ECM of the LEAN condition (small electromotive force:  0 V).
When the air–fuel ratio is RICHER than the stoichiometric air–fuel ratio the oxygen concentration in the ex-
haust gas in reduced and the oxygen sensor informs the ECM of the RICH condition (large electromotive
force:  1V). The ECM judges by the electromotive force from the oxygen sensor whether the air–fuel ratio
is RICH or LEAN and controls the injection time accordingly. However, if malfunction of the oxygen sensor
causes output of abnormal electromotive force, the ECM is unable to perform accurate air–fuel ratio control.
The heated oxygen sensors include a heater which heats the Zirconia element. The heater is controlled by
the ECM. When the intake air volume is low (the temp. of the exhaust gas is low) current flows to the heater
to heat the sensor for accurate oxygen concentration detection.

 

DTC No.

DTC Detecting Condition

Trouble Area

P0125

After the engine is warmed up, heated oxygen sensor (bank 1,

2 sensor 1) output does not indicate RICH even once when

conditions (a), (b), (c) and  (d) continue for at least 2 min.:

(a) Engine speed:   1,500 rpm or more

(b) Vehicle speed:  40 

∼

 100 km/h (25 

∼

 62 mph)

(c) Throttle valve does not fully closed

(d) 140 sec. or more after starting engine

Open or short  in  heated oxygen sensor (bank 1, 2 sensor 1)

circuit

Heated oxygen sensor (bank 1, 2 sensor 1)

DI09I–01