Lexus ES300 (2002 year). Manual — part 358

P21242 FI7210

Atmosphere

Flange
Platinum Electrode
Solid Electrolyte
(Zirconia Element)
Platinum Electrode
Heater
Coating (Ceramic)

Exhaust Gas

Cover

Ideal Air-Fuel Mixture

Output V

oltage

Richer - Air Fuel Ratio - Leaner

A00027

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-

DIAGNOSTICS

SFI SYSTEM (1MZ-FE)

205

2002 LEXUS ES300 REPAIR MANUAL (RM911U)

DTC

P0125

INSUFFICIENT COOLANT TEMP. FOR
CLOSE 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 cata-
lytic 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 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: < 0.45 V).
When the air-fuel ratio is RICHER than the stoichiometric air-fuel ratio the oxygen concentration in the ex-
haust gas is reduced and the oxygen sensor informs the ECM of the RICH condition (large electromotive
force: > 0.45 V). 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 sen-
sor causes output of abnormal electromotive force, the ECM is unable to perform accurate air-fuel ratio con-
trol.
The main 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 temperature 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 engine is warmed up, A/F sensor output* does not
change when conditions (a), (b), (c) and (d) continue for at
least 1.5 min:
*: Output value changes at inside of the ECM only

(a) Engine speed: 1,500 rpm or more

(b) Vehicle speed: 40 - 100 km/h (25 - 62 mph)

(c) Throttle valve is not fully closed

(d) 140 sec. or more after starting engine

Open or short in A/F sensor (bank 1, 2 sensor 1) circuit

A/F sensor (bank 1, 2 sensor 1)

Air induction system

Fuel pressure

Injector

Gas leakage on exhaust system

PCV hose connection

ECM

051M1-07

Vehicle speed

40 km/h
(24 mph)

Idling

2

IG SW OFF

100 sec.
or more

20 sec.
or more

20 sec.
or more

20 sec.
or more

20 sec.
or more

20 sec.
or more

30 sec.

1

3

3

3

4

4

5

A52172

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DIAGNOSTICS

SFI SYSTEM (1MZ-FE)

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2002 LEXUS ES300 REPAIR MANUAL (RM911U)

HINT:

After confirming DTC P0125, use the OBD II scan tool or hand-held tester to confirm voltage output
of the A/F sensor (bank 1, 2 sensor 1) from the CURRENT DATA.

The ECM controls the voltage of the AFR+, AFL+, AFR- and AFL- terminals of the ECM to the fixed
voltage. Therefore, it is impossible to confirm the A/F sensor output voltage without the OBD II scan
tool or hand-held tester.

OBD II scan tool (excluding hand-held tester) displays the one fifth of the A/F sensor output voltage
which is displayed on the hand-held tester.

CONFIRMATION DRIVING PATTERN

(a)

Switch the hand-held tester from the normal mode to the check mode. (See page

05-5

)

1

(b)

Start the engine and let the engine idle for 100 seconds or more.

2

(c)

Drive the vehicle at 40 km/h (24 mph) or more for 20 seconds or more.

3

(d)

Let the engine idle for 20 seconds or more.

4

(e)

Repeat the procedure

3 and

4 three times.

(f)

Let the engine idle for 30 seconds.

5

(g)

Check the O2 sensor output voltage.

HINT:
If a malfunction exists, the check engine warning light comes on.
NOTICE:
If the conditions on this test are not strictly followed, the malfunction will not be detected.

A61586

E9

E6

E8

ECM

AFR+

AFR-

HAFL

AFL+

AFL-

E9

E9

E9

E9

E9

MREL

E1

22

30

4

23

31

3

8

1

Engine Room J/B

(*1)

A

A

A

J11 J/C

EF

BR

B

B

2

3

1

4

B

W

O

1

6

6

1

1

1

1

1

1

1B

1A

4

2

A/F

Battery

BC

FL MAIN

B-G

Engine
Room J/B

B-G

Engine
Room R/B

L

W-B

1

2

3

5

1J

1L

1L

B-W

B-R

A/F
Sensor
(B1S1)

A/F HTR

Relay

(*1)

2

3

1

4

B-W

B-R

*1: Shielded

HAFR

A/F

Sensor

(B2S1)

Engine
Room R/B

BR

BR

BR

BR

A

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DIAGNOSTICS

SFI SYSTEM (1MZ-FE)

207

2002 LEXUS ES300 REPAIR MANUAL (RM911U)

WIRING DIAGRAM

-

DIAGNOSTICS

SFI SYSTEM (1MZ-FE)

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2002 LEXUS ES300 REPAIR MANUAL (RM911U)

INSPECTION PROCEDURE

HINT:
Read freeze frame data using hand-held tester or OBD II scan tool. Because freeze frame records the en-
gine 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.

1

CHECK OTHER DTC OUTPUT(BESIDES DTC P0125)

YES

GO TO RELEVANT DTC CHART

NO

2

READ VALUE OF A/FS(B1S1, B2S1)

(a)

Warm up the A/F sensor with the engine speed at 2,500 rpm for approx. 90 sec.

(b)

Read the voltage value of the A/F sensor on the screen of OBD II scan tool or hand-held tester when
you perform all the following conditions.

HINT:
The voltage of the AFR+ or AFL+ terminal of the ECM is fixed at 3.3 V and the voltage of the AFR- or AFL-
terminal is fixed at 3.0 V. Therefore, it is impossible to check the A/F sensor output voltage at the terminals
(AFR+, AFL+/AFR-, AFL-) of the ECM.

Result:

Condition

A/F Sensor Voltage Value

Engine idling

Not remains at 3 30 V (0 660 V*)

Engine racing

Not remains at 3.30 V (0.660 V*)

Not remains at 3 8 V (0 76 V*) or more

Driving at engine speed 1,500 rpm or more and vehicle
speed 40 km/h (25 mph) or more, and operate throttle valve
open and close

Not remains at 3.8 V (0.76 V*) or more

Not remains at 2.8 V (0.56 V*) or less

*: When you use OBD II scan tool (excluding TOYOTA hand-held tester)

HINT:

During fuel enrichment, there is a case that the output voltage of the A/F sensor is below 2.8 V (0.56
V*), it is normal.

During fuel cut, there is a case that the output voltage of the A/F sensor is above 3.8 V (0.76 V*), it
is normal.

If the output voltage of the A/F sensor remains at 3.30 V (0.660 V*) even after performing all the above
conditions, the A/F sensor circuit may be open.

If the output voltage of the A/F sensor remains at 3.8 V (0.76 V*) or more, or 2.8 V (0.56 V*) or less
even after performing all the above conditions, the A/F sensor circuit may be short.

*: When you use the OBD II scan tool (excluding hand-held tester).

OK

Go to step 10

NG

3

CHECK CONNECTION OF PCV HOSE

NG

REPAIR OR REPLACE PCV HOSE

OK