Toyota FJ Cruiser (GSJ 10, 15 series). Manual - part 50

1GR-FE ENGINE CONTROL SYSTEM – SFI SYSTEM

ES–155

(a) Disconnect the B34 or B36 HO2 sensor connector.
(b) Turn the ignition switch ON.
(c) Measure the voltage between the +B terminal of the HO2

sensor connector and body ground.
Standard Voltage

(d) Turn the ignition switch OFF.
(e) Disconnect the B1 and B2 ECM connectors.
(f)

Check the resistance.
Standard Resistance (Check for open)

Standard Resistance (Check for short)

(g) Reconnect the HO2 sensor connector.
(h) Reconnect the ECM connectors.

CHECK HARNESS AND CONNECTOR (HEATED OXYGEN SENSOR - ECM)

B36

Wire Harness Side:

Front View

ECM Connector

Bank 1

B34 Bank 2

HO2 Sensor Connector

HT1B or
HT2B

OX1B or
OX2B

HT2B

OX1B

OX2B

HT1B

A116170E04

Terminal Connections

Specified Conditions

+B (B36-2) - Body ground

11 to 14 V

+B (B34-2) - Body ground

Terminal Connections

Specified Conditions

HT1B (B36-1) - HT1B (B1-1)

Below 1

Ω

OX1B (B36-3) - OX1B (B1-18)

E2 (B36-4) - E2 (B1-28)

HT2B (B34-1) - HT2B (B2-5)

OX2B (B34-3) - OX2B (B2-33)

E2 (B34-4) - E2 (B1-28)

Terminal Connections

Specified Conditions

HT1B (B36-1) or HT1B (B1-1) - Body ground

10 k

Ω or higher

OX1B (B36-3) or OX1B (B1-18) - Body ground

HT2B (B34-1) or HT2B (B2-5) - Body ground

OX2B (B34-3) or OX2B (B2-33) - Body ground

ES–156

1GR-FE ENGINE CONTROL SYSTEM – SFI SYSTEM

Reference (System Diagram of Bank 1 Sensor 2):

From
Battery

EFI

Ground

Heater

Sensor

HO2 Sensor

EFI NO. 2

OX1B

MREL

HT1B

OX1B

HT1B

ECM

Duty
Control

A103832E33

REPAIR OR REPLACE HARNESS OR
CONNECTOR

REPLACE HEATED OXYGEN SENSOR (See page

EC-24

)

1GR-FE ENGINE CONTROL SYSTEM – SFI SYSTEM

ES–157

DESCRIPTION

The fuel trim is related to the feedback compensation value, not to the basic injection time. The fuel trim
consists of both the short-term and long-term fuel trims.
The short-term fuel trim is fuel compensation that is used to constantly maintain the air-fuel ratio at
stoichiometric levels. The signal from the Air-Fuel Ratio (A/F) sensor indicates whether the air-fuel ratio is
rich or lean compared to the stoichiometric ratio. This triggers a reduction in the fuel injection volume if the
air-fuel ratio is rich and an increase in the fuel injection volume if it is lean.
Factors such as individual engine differences, wear over time and changes in operating environment
cause short-term fuel trim to vary from the central value. The long-term fuel trim, which controls overall
fuel compensation, compensates for long-term deviations in the fuel trim from the central value caused by
the short- term fuel trim compensation.
If both the short-term and long-term fuel trims are lean or rich beyond predetermined values, it is
interpreted as a malfunction, and the ECM illuminates the MIL and sets a DTC.

HINT:
•

When DTC P0171 or P0174 is set, the actual air-fuel ratio is on the lean side. When DTC P0172 or
P0175 is set, the actual air-fuel ratio is on the rich side.

•

If the vehicle runs out of fuel, the air-fuel ratio is lean and DTC P0171 or P0174 may be set. The MIL is
then illuminated.

•

When the total of the short-term and long-term fuel trim values is within the malfunction threshold (and
the engine coolant temperature is more than 75

°C [167°F]), the system is functioning normally.

DTC

P0171

System Too Lean (Bank 1)

DTC

P0172

System Too Rich (Bank 1)

DTC

P0174

System Too Lean (Bank 2)

DTC

P0175

System Too Rich (Bank 2)

DTC No.

DTC Detection Conditions

Trouble Areas

P0171
P0174

With warm engine and stable air-fuel ratio feedback, fuel trim
considerably in error to lean side (2 trip detection logic)

•

Air induction system

•

Injector blockage

•

Mass Air Flow (MAF) meter

•

Engine Coolant Temperature (ECT) sensor

•

Fuel pressure

•

Gas leakage from exhaust system

•

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

•

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

•

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

•

A/F sensor heater relay

•

A/F sensor heater and A/F sensor heater relay circuits

•

PCV valve and hose

•

PCV hose connections

•

ECM

P0172
P0175

With warm engine and stable air-fuel ratio feedback, fuel trim
considerably in error to rich side (2 trip detection logic)

•

Injector leakage or blockage

•

MAF meter

•

ECT sensor

•

Ignition system

•

Fuel pressure

•

Gas leakage from exhaust system

•

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

•

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

•

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

•

A/F sensor heater relay

•

A/F sensor heater and A/F sensor heater relay circuits

•

ECM

ES–158

1GR-FE ENGINE CONTROL SYSTEM – SFI SYSTEM

MONITOR DESCRIPTION

Under closed-loop fuel control, fuel injection volumes that deviate from those estimated by the ECM
cause changes in the long-term fuel trim compensation value. The long-term fuel trim is adjusted when
there are persistent deviations in the short-term fuel trim values. Deviations from the ECM's estimated fuel
injection volumes also affect the average fuel trim learning value, which is a combination of the average
short-term fuel trim (fuel feedback compensation value) and the average long-term fuel trim (learning
value of the air- fuel ratio). If the average fuel trim learning value exceeds the malfunction thresholds, the
ECM interprets this a fault in the fuel system and sets a DTC.
Example:
The average fuel trim learning value is more than +35 % or less than -35 %, the ECM interprets this as a
fuel system malfunction.

MONITOR STRATEGY

Related DTCs

P0171: Fuel trim Lean (bank 1)
P0172: Fuel trim Rich (bank 1)
P0174: Fuel trim Lean (bank 2)
P0175: Fuel trim Rich (bank 2)

Required Sensors/Components (Main)

Fuel system

Required Sensors/Components (Related)

A/F sensor, Mass air flow meter, Crankshaft position sensor

Frequency of Operation

Continuous

Duration

Within 10 seconds

MIL Operation

2 driving cycles

Sequence of Operation

None

Fuel Compensation
Amount

+35%:
Malfunction Threshold
of LEAN Condition

-35%:
Malfunction Threshold
of RICH Condition

1.35

1.0

0.65

P0171, P0174

P0172, P0175

A121607E01

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