Lexus ES300 (2002 year). Service manual - part 361

Ie-4-2-D

A30590

HT

+B

E1

OX

A52108

A56997

Bank 1

Bank 2

HT

+B

OX

E1

HT

+B

OX

E1

A54408

E2

HT2B

HT1B

E8

05-64

-

DIAGNOSTICS

SFI SYSTEM (1MZ-FE)

217

2002 LEXUS ES300 REPAIR MANUAL   (RM911U)

2

INSPECT OXYGEN NO.2 SENSOR

(a)

Disconnect the oxygen sensor connector.

(b)

Measure resistance between the terminals HT and +B of
the oxygen sensor.
Resistance: 11 - 16 

Ω

 (20



C)

NG

REPLACE OXYGEN NO.2 SENSOR

OK

3

CHECK HARNESS AND CONNECTOR(ECM - OXYGEN SENSOR)

(a)

Disconnect the oxygen sensor connector.

(b)

Disconnect the ECM E8 connector.

(c)

Check for open between the terminals HT of the oxygen
sensor connector and HT1B, HT2B of the ECM connec-
tor.
Resistance: 1 

Ω

 or less

(d)

Check for short between the terminals HT1B, HT2B and
E2 of the ECM connector.
Resistance: 1 M

Ω

 or more

NG

REPAIR OR REPLACE HARNESS AND
CONNECTOR

OK

A59656

5

A56997

Bank 1

Bank 2

HT

+B

OX

E1

HT

+B

OX

E1

-

DIAGNOSTICS

SFI SYSTEM (1MZ-FE)

05-65

218

2002 LEXUS ES300 REPAIR MANUAL   (RM911U)

4

CHECK HARNESS AND CONNECTOR(OXYGEN SENSOR - E.F.I. ECU RELAY)

(a)

Disconnect the battery negative (-) terminal.

(b)

Disconnect the oxygen sensor connector.

(c)

Check for open between the terminals 5 of the E.F.I. ECU
relay side connector and +B of the oxygen sensor con-
nector.
Resistance: 1 

Ω

 or less

NOTICE:
Do not insert the tester leads hard in the procedure (c), or
the holder may be damaged.

NG

REPAIR OR REPLACE HARNESS AND
CONNECTOR

OK

CHECK CHECK FOR ECM POWER SOURCE CIRCUIT

05-66

-

DIAGNOSTICS

SFI SYSTEM (1MZ-FE)

219

2002 LEXUS ES300 REPAIR MANUAL   (RM911U)

DTC

P0171

SYSTEM TOO LEAN(FUEL TRIM)(BANK1)

DTC

P0172

SYSTEM TOO RICH(FUEL TRIM)(BANK1)

DTC

P0174

SYSTEM TOO LEAN (FUEL TRIM)(BANK2)

DTC

P0175

SYSTEM TOO RICH (FUEL TRIM)(BANK2)

CIRCUIT DESCRIPTION

Fuel trim refers to the feedback compensation value compared against the basic injection time. Fuel trim
includes short-term fuel trim and long-term fuel trim.
Short-term  fuel trim is the short-term fuel compensation used to maintain the air-fuel ratio at its ideal
theoretical value. The signal from the heated oxygen sensor indicates whether the air-fuel ratio is RICH or
LEAN compared to the ideal theoretical value, triggering a reduction in fuel volume if the air-fuel ratio is rich,
and an increase in fuel volume if it is lean.
Long-term  fuel trim is overall fuel compensation carried out long-term to compensate for continual deviation
of the short-term fuel trim form the central value due to individual engine differences, wear over time and
changes in the usage environment.
If both the short-term fuel trim and long-term fuel trim are LEAN or RICH beyond a certain value, it is de-
tected as a malfunction and the check engine warning (MIL) lights up.

DTC No.

DTC Detecting Condition

Trouble Area

P0171
P0174

When air fuel ratio feedback is stable after warming up engine,
fuel trim is considerably in error on RICH side 
(2 trip detection logic)

Air intake (hose loose)

Fuel line pressure

Injector blockage

Open or short in A/F sensor circuit

A/F sensor malfunction

Intake air flow meter

E.F.I. engine coolant temperature sensor

Gas leakage on exhaust system

PCV hose connection

P0172
P0175

When air fuel ratio feedback is stable after warming up engine,
fuel trim is considerably in error on LEAN side 
(2 trip detection logic)

Air induction system

Fuel line pressure

Injector blockage

Open or short in A/F sensor circuit

A/F sensor malfunction

Intake air flow meter

E.F.I. engine coolant temperature sensor

Gas leakage on exhaust system

PCV hose connection

HINT:
If the total of the short-term fuel trim value and long-term fuel trim value is within 

±

 25 %, the system is func-

tioning normally.

WIRING DIAGRAM

Refer to DTC P0125 on page 

05-52

.

051X8-06

-

DIAGNOSTICS

SFI SYSTEM (1MZ-FE)

05-67

220

2002 LEXUS ES300 REPAIR MANUAL   (RM911U)

INSPECTION PROCEDURE

HINT:
Read freed 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 run-
ning or stopped, the engine warmed up or not, the air-fuel ratio lean or rich, etc. at the time of the malfunction.

1

CHECK AIR INDUCTION SYSTEM (See page 

11-1

)

NG

REPAIR OR REPLACE AIR INDUCTION SYSTEM

OK

2

CHECK CONNECTION OF PCV HOSE

NG

REPAIR OR REPLACE PCV HOSE

OK

3

INSPECT FUEL INJECTOR ASSY (See page 

11-7

)

NG

REPLACE FUEL INJECTOR ASSY

OK

4

INSPECT INTAKE AIR FLOW METER SUB-ASSY (See page 

10-2

)

NG

REPLACE INTAKE AIR FLOW METER
SUB-ASSY

OK

5

INSPECT E.F.I.  ENGINE COOLANT TEMPERATURE SENSOR 
(See page 

10-2

)

NG

REPLACE E.F.I.  ENGINE COOLANT
TEMPERATURE SENSOR

OK

6

CHECK FOR SPARK AND IGNITION (See page 

18-1

)

NG

GO TO IGNITION SYSTEM

OK