Toyota FJ Cruiser (GSJ 10, 15 series). Instruction - part 46

1GR-FE ENGINE CONTROL SYSTEM  –  SFI SYSTEM

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DTC No.

DTC Detection Conditions

Trouble Areas

P0136
P0156

•

Abnormal voltage output:

During active air-fuel ratio control, following conditions 
(a) and (b) met for certain period of time (2 trip 
detection logic)
(a) Heated Oxygen (HO2) sensor voltage does not 
decrease to less than 0.21 V
(b) HO2 sensor voltage does not increase to more than 
0.59 V

•

Low impedance:

Sensor impedance less than 5 

Ω for more than 30 

seconds when ECM presumes sensor to being 
warmed up and operating normally (2 trip detection 
logic)

•

Open or short in HO2 sensor (bank 1, 2 sensor 2) circuit

•

HO2 sensor (bank 1, 2 sensor 2)

•

HO2 sensor heater (bank 1, 2 sensor 2)

•

Air-Fuel Ratio (A/F) sensor (bank 1, 2 sensor 1)

•

EFI  relay

•

Gas leakage from exhaust system

P0137
P0157

•

Low voltage (open):

During active air-fuel ratio control, following conditions 
(a) and (b) met for certain period of time (2 trip 
detection logic)
(a) HO2 sensor voltage output less than 0.21 V
(b) Target air-fuel ratio rich

•

High impedance:

Sensor impedance 15 k

Ω or more for more than 90 

seconds when ECM presumes sensor to being 
warmed up and operating normally (2 trip detection 
logic)

•

Open in HO2 sensor (bank 1, 2 sensor 2) circuit

•

HO2 sensor (bank 1, 2 sensor 2)

•

HO2 sensor heater (bank 1, 2 sensor 2)

•

EFI  relay

•

Gas leakage from exhaust system

P0138
P0158

•

High voltage (short):

During active air-fuel ratio control, following conditions 
(a) and (b) met for certain period of time (2 trip 
detection logic)
(a) HO2 sensor voltage output 0.59 V or more
(b) Target air-fuel ratio lean

•

Extremely high voltage (short):

HO2 sensor voltage output exceeds 1.2 V for more 
than 10 seconds (2 trip detection logic)

•

Short in HO2 sensor (bank 1, 2 sensor 2) circuit

•

HO2 sensor (bank 1, 2 sensor 2)

•

ECM internal circuit malfunction

Atmospheric Air

Housing

Platinum Electrode

Output Voltage Ideal Air-fuel Mixture

Exhaust Gas

Solid Electrolyte 
(Zirconia Element)

Coating (Ceramic)

Heater

Cover

Richer - Air-fuel Ratio - Leaner

A115539E03

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1GR-FE ENGINE CONTROL SYSTEM  –  SFI SYSTEM

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MONITOR DESCRIPTION

1.

Active Air-Fuel Ratio Control
The ECM usually performs air-fuel ratio feedback control so that the Air-Fuel Ratio (A/F) sensor 
output indicates a near stoichiometric air-fuel level. This vehicle includes active air-fuel ratio control in 
addition to regular air-fuel ratio control. The ECM performs active air-fuel ratio control to detect any 
deterioration in the Three-Way Catalytic Converter (TWC) and Heated Oxygen (HO2) sensor 
malfunctions (refer to the diagram below).
Active air-fuel ratio control is performed for approximately 15 to 20 seconds while driving with a warm 
engine. During active air-fuel ratio control, the air-fuel ratio is forcibly regulated to become lean or rich 
by the ECM. If the ECM detects a malfunction, one of the following DTCs is set: DTC P0136 or 
P0156 (abnormal voltage output), P0137 or P0157 (open circuit) or P0138 or P0158 (short circuit).

2.

Abnormal Voltage Output of HO2 Sensor (DTCs P0136 and P0156)
While the ECM is performing active air-fuel ratio control, the air-fuel ratio is forcibly regulated to 
become rich or lean. If the sensor is not functioning properly, the voltage output variation is small. For 
example, when the HO2 sensor voltage does not decrease to less than 0.21 V and does not increase 
to more than 0.59 V during active air-fuel ratio control, the ECM determines that the sensor voltage 
output is abnormal and sets DTCs P0136 and P0156.

3.

Open or Short in Heated Oxygen (HO2) Sensor Circuit (DTCs P0137 and P0157 or P0138 and 
P0158)

During active air-fuel ratio control, the ECM calculates the Oxygen Storage Capacity (OSC)

*

 of the 

Three-Way Catalytic Converter (TWC) by forcibly regulating the air-fuel ratio to become rich or lean.
If the HO2 sensor has an open or short, or the voltage output of the sensor noticeably decreases, the 
OSC indicates an extraordinarily high value. Even if the ECM attempts to continue regulating the air-
fuel ratio to become rich or lean, the HO2 sensor output does not change.
While performing active air-fuel ratio control, when the target air-fuel ratio is rich and the HO2 sensor 
voltage output is 0.21 V or less (lean), the ECM interprets this as an abnormally low sensor output 
voltage and sets DTC P0137 or P0157. When the target air-fuel ratio is lean and the voltage output is 
0.59 V or more (rich) during active air-fuel ratio control, the ECM determines that the sensor voltage 
output is abnormally high, and sets DTC P0138 or P0158.
HINT:
DTC P0138 or P0158 is also set if the HO2 sensor voltage output is more than 1.2 V for 10 seconds 
or more.

HO2 SENSOR CIRCUIT MALFUNCTION (P0136 and P0156: ABNORMAL VOLTAGE)

Active air fuel 
ratio control

HO2 sensor 
voltage

Off

Normal

0.59 V

0.21 V

Abnormal

15 to 20 seconds

Operation

A115540E01

1GR-FE ENGINE CONTROL SYSTEM  –  SFI SYSTEM

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*

: The TWC has the capability to store oxygen. The OSC and the emission purification capacity of the 

TWC are mutually related. The ECM determines whether the catalyst has deteriorated, based on the 
calculated OSC value (See page 

ES-210

).

HO2 SENSOR CIRCUIT LOW VOLTAGE (P0137 and P0157: OPEN)

Active air fuel 
ratio control

HO2 sensor 
voltage

Target air fuel ratio

Stoichiometric 
Air Fuel Level

Off

0.21 V

HO2 SENSOR CIRCUIT HIGH VOLTAGE (P0138 and P0158: SHORT)

Active air fuel 
ratio control

HO2 sensor 
voltage

Target air fuel ratio

Stoichiometric 
Air Fuel Level

Off

0.59 V

15 to 20 seconds

Operation

Operation

Lean

Normal

Abnormal

Abnormal

Abnormal

Normal

Rich

A115541E01

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1GR-FE ENGINE CONTROL SYSTEM  –  SFI SYSTEM

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4.

High or Low Impedance of Heated Oxygen (HO2) 
Sensor (DTCs P0136 and P0156 or P0137 and P0157)
During normal air-fuel ratio feedback control, there are 
small variations in the exhaust gas oxygen 
concentration. In order to continuously monitor the slight 
variation of the HO2 sensor signal while the engine is 

running, the impedance

*

 of the sensor is measured by 

the ECM. The ECM determines that there is a 
malfunction in the sensor when the measured 
impedance deviates from the standard range.

*

: The effective resistance in an alternating current 

electrical circuit.
HINT:
•

The impedance cannot be measured using an 
ohmmeter.

•

DTCs P0136 and P0156 indicate the deterioration of 
the HO2 sensor. The ECM sets the DTCs by 
calculating the impedance of the sensor when the 
typical enabling conditions are satisfied (2 driving 
cycle).

•

DTCs P0137 and P0157 indicate an open or short 
circuit in the HO2 sensor (2 driving cycle). The ECM 
sets the DTCs when the impedance of the sensor 
exceeds the threshold 15 k

Ω.

MONITOR STRATEGY

Relationship between element 

temperature and impedance:

DTC Detection Area

°C (°F)

(Ω)

15,000

1,000

100

10

5

300

(572)

400

(752)

500

(932)

600

(1,112)

800

(1,472)

700

(1,292)

A076841E04

Related DTCs

P0136: Heated oxygen sensor output voltage (Output voltage) (bank 1)
P0136: Heated oxygen sensor impedance (Low) (bank 1)
P0137: Heated oxygen sensor output voltage (Low voltage) (bank 1)
P0137: Heated oxygen sensor impedance (High) (bank 1)
P0138: Heated oxygen sensor output voltage (High voltage) (bank 1)
P0138: Heated oxygen sensor output voltage (Extremely high) (bank 1)
P0156: Heated oxygen sensor output voltage (Output voltage) (bank 2)
P0156: Heated oxygen sensor impedance (Low) (bank 2)
P0157: Heated oxygen sensor output voltage (Low voltage) (bank 2)
P0157: Heated oxygen sensor impedance (High) (bank 2)
P0158: Heated oxygen sensor output voltage (High voltage) (bank 2)
P0158: Heated oxygen sensor impedance (Extremely high) (bank 2)

Required Sensors/Components (Main)

Heated oxygen sensor

Required Sensors/Components (Related)

Crankshaft position sensor, engine coolant temperature sensor, mass air flow meter 
and throttle position sensor

Frequency of Operation

Once per driving cycle: Active air-fuel ratio control detection
Continuous: Others

Duration

20 seconds: Heated oxygen sensor output (Output voltage, High voltage, Low 
voltage)
30 seconds: Heated oxygen sensor impedance (Low)
90 seconds: Heated oxygen sensor impedance (High)
10 seconds: Heated oxygen sensor voltage (Extremely high)

MIL Operation

2 driving cycles

Sequence of Operation

None