Toyota FJ Cruiser (GSJ 10, 15 series). Instruction - part 45

1GR-FE ENGINE CONTROL SYSTEM  –  SFI SYSTEM

ES–135

ES

HINT:
This DTC relates to the thermostat.

DESCRIPTION

This DTC is set when the Engine Coolant Temperature (ECT) does not reach 75

°C (167°F) despite 

sufficient engine warm-up time.

MONITOR DESCRIPTION

The ECM estimates the ECT based on the starting temperature, engine loads, and engine speeds. The 
ECM then compares the estimated temperature with the actual ECT. When the estimated ECT reaches 
75

°C (167°F), the ECM checks the actual ECT. If the actual ECT is less than 75°C (167°F), the ECM 

interprets this as a malfunction in the thermostat or the engine cooling system and sets the DTC.

DTC

P0128

Coolant Thermostat (Coolant Temperature 
Below Thermostat Regulating Temperature)

DTC No.

DTC Detection Conditions

Trouble Areas

P0128

Conditions (a), (b) and (c) are met for 5 seconds (2 rip detection logic)
(a) Cold start
(b) Engine warmed up
(c) ECT less than 75

°C (167°F)

•

Thermostat

•

Cooling system

•

ECT sensor

•

ECM

Threshold 
(75°C (167°F))

ECT

Time

DTC set (after 2 driving cycles)

Indicated ECT reading

Estimated ECT

5 seconds

A115933E01

ES–136

1GR-FE ENGINE CONTROL SYSTEM  –  SFI SYSTEM

ES

MONITOR STRATEGY

TYPICAL ENABLING CONDITIONS

TYPICAL MALFUNCTION THRESHOLDS

INSPECTION PROCEDURE

HINT:
Read freeze frame data using an intelligent tester. Freeze frame data record the engine condition when 
malfunctions are detected. When troubleshooting, freeze frame data can help determine if the vehicle was 
moving or stationary, if the engine was warmed up or not, if the air-fuel ratio was lean or rich, and other 
data, from the time the malfunction occurred.

Related DTCs

P0128: Coolant Thermostat

Required Sensors/Components (Main)

Engine Coolant Temperature (ECT) sensor, Thermostat

Required Sensors/Components (Related)

Intake Air Temperature (IAT) sensor, Vehicle speed sensor

Frequency of Operation

Once per driving cycle

Duration

900 seconds

MIL Operation

2 driving cycles

Sequence of Operation

None

Monitor runs whenever following DTCs not present

P0010, P0020 (OCV Bank 1, 2)
P0011 (VVT System 1 - Advance)
P0012 (VVT System 1 - Retard)
P0021 (VVT System 2 - Advance)
P0022 (VVT System 2 - Retard)
P0031, P0032, P0051, P0052 (A/F sensor heater - Sensor 1)
P0100 - P0103 (MAF meter)
P0110 - P0113 (IAT sensor)
P0115 - P0118 (ECT sensor)
P0125 (Insufficient ECT for closed loop)
P0171, P0172, P0174, P0175 (Fuel system)
P0300 - P0306 (Misfire)
P0335 (CKP sensor)
P0340 (CMP sensor)
P0351 - P0356 (igniter)
P0500 (VSS)
P2196, P2198 (A/F sensor - rationality)
P2A00, P2A03 (A/F sensor - slow response)

Battery voltage

11 V or more

Either of following conditions 1 or 2 met:

-

1. All of following conditions met:

-

(a) ECT at engine start - IAT at engine start

-15

° to 7°C (-27° to 12.6°F)

(b) ECT at engine start

-10

° to 56°C (14° to 133°F)

(c) IAT at engine start

-10

° to 56°C (14° to 133°F)

2. All of following conditions met:

-

(a) ECT at engine start - IAT at engine start

More than 7

°C (12.6°F)

(b) ECT at engine start

56

°C (133°F) or less

(c) IAT at engine start

-10

°C (14°F) or more

Accumulated time with 80 mph (128 km/h) or more of vehicle speed

Less than 20 seconds

Duration that following conditions A and B met

5 seconds or more

A. Simulated ECT

75

°C (167°F) or more

B. ECT sensor output

Less than 75

°C (167°F)

1GR-FE ENGINE CONTROL SYSTEM  –  SFI SYSTEM

ES–137

ES

(a) Connect an intelligent tester to the DLC3.
(b) Turn the ignition switch ON.
(c) Turn the tester ON.
(d) Select the following menu items: DIAGNOSIS / 

ENHANCED OBD II / DTC INFO / CURRENT CODES.

(e) Read the DTC.

Result

HINT:
If any DTCs other than P0128 are output, troubleshoot 
those DTCs first.

B

A

(a) Check for defects in the cooling system that might cause 

the system to be too cold, such as abnormal radiator fan 
operation or any modifications.

NG

OK

(a) Remove the water inlet with thermostat (See page 

CO-

12

).

(b) Check the valve opening temperature of the thermostat.

Standard:

80

° to 84°C (176° to 183°F)

HINT:
In addition to the above check, confirm that the valve is 
completely closed when the temperature is below the 
standard.

(c) Reinstall the water inlet with thermostat (See page 

CO-

13

).

NG

OK

1

CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0128)

Display (DTC Output)

Proceed to

P0128

A

P0128 and other DTCs

B

GO TO DTC CHART (See page 

ES-57

)

2

CHECK COOLING SYSTEM

REPAIR OR REPLACE COOLING SYSTEM

3

INSPECT WATER INLET WITH THERMOSTAT (THERMOSTAT)

REPLACE WATER INLET WITH 
THERMOSTAT (See page 

CO-12

)

REPLACE ECM (See page 

ES-446

)

ES–138

1GR-FE ENGINE CONTROL SYSTEM  –  SFI SYSTEM

ES

HINT:
Sensor 2 refers to the sensor mounted behind the Three-Way Catalytic Converter (TWC) and located far 
from the engine assembly.

DESCRIPTION

In order to obtain a high purification rate of the carbon monoxide (CO), hydrocarbon (HC) and nitrogen 
oxide (NOx) components in the exhaust gas, a TWC (Three-Way Catalytic Converter) is used. For the 
most efficient use of the TWC, the air-fuel ratio must be precisely controlled so that it is always close to 
the stoichiometric air-fuel level. For the purpose of helping the ECM to deliver accurate air-fuel ratio 
control, a Heated Oxygen (HO2) sensor is used.
The HO2 sensor is located behind the TWC, and detects the oxygen concentration in the exhaust gas. 
Since the sensor is integrated with the heater that heats the sensing portion, it is possible to detect the 
oxygen concentration even when the intake air volume is low (the exhaust gas temperature is low).
When the air-fuel ratio becomes lean, the oxygen concentration in the exhaust gas is rich. The HO2 
sensor informs the ECM that the post-TWC air-fuel ratio is lean (low voltage, i.e. less than 0.45 V).
Conversely, when the air-fuel ratio is richer than the stoichiometric air-fuel level, the oxygen concentration 
in the exhaust gas becomes lean. The HO2 sensor informs the ECM that the post-TWC air-fuel ratio is 
rich (high voltage, i.e. more than 0.45 V). The HO2 sensor has the property of changing its output voltage 
drastically when the air-fuel ratio is close to the stoichiometric level.
The ECM uses the supplementary information from the HO2 sensor to determine whether the air-fuel ratio 
after the TWC is rich or lean, and adjusts the fuel injection time accordingly. Thus, if the HO2 sensor is 
working improperly due to internal malfunctions, the ECM is unable to compensate for deviations in the 
primary air-fuel ratio control.

DTC

P0136

Oxygen Sensor Circuit Malfunction (Bank 1 
Sensor 2)

DTC

P0137

Oxygen Sensor Circuit Low Voltage (Bank 1 
Sensor 2)

DTC

P0138

Oxygen Sensor Circuit High Voltage (Bank 1 
Sensor 2)

DTC

P0156

Oxygen Sensor Circuit Malfunction (Bank 2 
Sensor 2)

DTC

P0157

Oxygen Sensor Circuit Low Voltage (Bank 2 
Sensor 2)

DTC

P0158

Oxygen Sensor Circuit High Voltage (Bank 2 
Sensor 2)