Toyota Sequoia (2005). Manual - part 84

–

DIAGNOSTICS

ENGINE

DI–139

333

DTC

P0125

Insufficient Coolant Temperature
 for Closed Loop Fuel Control

CIRCUIT DESCRIPTION

Refer to DTC P0115 on page 

DI–119

.

DTC No.

DTC Detection Condition

Trouble Area

If THW or THA is less than –19.45

°

C (–3

°

F) at engine start

and 20 min. or more after starting engine, engine coolant
temp. sensor value is 20

°

C (68

°

F) or less (2 trip detection

logic)

P0125

If THW and THA is between –19.45

°

C (–3

°

F) and –8.34

°

C

(17

°

F) at engine start, 5 min. or more after starting engine

and engine coolant temp. sensor value is 20

°

C (68

°

F) or

less (2 trip detection logic)

Cooling system

Engine coolant temperature sensor

Thermostat

If THW and THA greater than –8.34

°

C (17

°

F) at engine

start and 2 min. or more after starting engine, engine cool-
ant temp. sensor value is 20

°

C (68

°

F) or less (2 trip detec-

tion logic)

MONITOR DESCRIPTION

The ECT (Engine Coolant Temperature) sensor is used to monitor the temperature of the engine coolant.
The resistance of the sensor varies with the actual coolant temperature. The ECM applies a voltage to the
sensor and the varying resistance of the sensor cause the signal voltage to vary. The ECM monitors the ECT
signal voltage after engine start–up.

 

If, after sufficient time has passed, the sensor still reports that the engine

is not warmed up enough for closed–loop fuel control after sufficient time has passed, the ECM interprets
this as a fault in the sensor or cooling system and sets a DTC.
Example:
The engine coolant temperature was 0



C (32



F) at engine start. After 5 min. running time, the ECT sensor

still indicates that the engine is not warmed up enough to begin air fuel ratio feedback control of the air–fuel
ratio. The ECM interprets this as a fault in the sensor or cooling system and will set a DTC.

MONITOR STRATEGY

Related DTCs

P0125

Insufficient coolant temperature for closed loop

fuel control

Required sensors/components

Main sensors/components

Engine coolant temperature sensor, Cooling sys-

tem, Thermostat

Required sensors/com onents

Related sensors/components

Mass air flow

 

meter

Frequency of operation

Continuous

2 min. (at engine start, engine coolant or intake air temperature of –8.34

°

C (17

°

F) or more)

Duration

2 min. (at engine start, engine coolant or intake air tem erature of –8.34 C (17 F) or more)

5 min. (at engine start, engine coolant or intake air temperature of –19.45 to –8.34

°

C (–3 to 17

°

F))

Duration

5 min. (at engine start, engine coolant or intake air tem erature of  19.45 to  8.34 C ( 3 to 17 F))

20 min. (at engine start, engine coolant or intake air temperature of less than –19.45

°

C (–3

°

F))

MIL operation

2 driving cycles

Sequence of operation

None

DICEP–02

DI–140

–

DIAGNOSTICS

ENGINE

334

TYPICAL ENABLING CONDITIONS

It

Specification

Item

Minimum

Maximum

The monitor will run whenever this DTC is
not present

See page 

DI–18

Fuel cut

OFF

Engine

Running

TYPICAL MALFUNCTION THRESHOLDS

Detection Criteria

Threshold

Time until ”engine coolant temperature” detection temperature reaches feedback start temperature

When the temperature at the time of engine starting is 

–8.34

°

C (17

°

F) or more

Engine coolant temperature is less than ”closed–loop enable temperature” 

when 2 min. or more after engine start

When the temperature at the time of engine starting is 

–19.45 to –8.34

°

C (–3 to 17

°

F)

Engine coolant temperature is less than ”closed–loop enable temperature” 

when 5 min. or more after engine start

When the temperature at the time of engine starting is 

–19.45

°

C (–3

°

F) or less

Engine coolant temperature is less than ”closed–loop enable temperature” 

when 20 min. or more after engine start

INSPECTION PROCEDURE

HINT:

If DTC P0115, P0116, P0117, P0118 and P0125 are output simultaneously, engine coolant tempera-
ture sensor circuit may be open or short. Perform the troubleshooting of DTC P0115, P0117 or P0118
first.

Read freeze frame data using 

the hand−held tester

. Freeze frame data records the engine conditions

when a malfunction is detected. When troubleshooting, freeze frame data can help determine if the
vehicle was running or stopped, if the engine was warmed up or not, if the air–fuel ratio was lean or
rich, as well as other data from the time when a malfunction occurred.

1

Are there any other codes (besides DTC P0125) being output?

PREPARATION:
(a)

Connect the hand–held tester to the DLC3.

(b)

Turn the ignition switch ON and push the hand–held tester main switch ON.

(c)

When using hand–held tester, enter the following menu: DIAGNOSIS / ENHANCED OBD II / DTC
INFO / CURRENT CODES.

CHECK:
Read the DTCs using the hand–held tester.
RESULT:

Display (DTC output)

Proceed to

P0125

A

”P0125” and other DTCs

B

HINT:
If any other codes besides ”P0125” are output, perform the troubleshooting for those DTCs first.

B

Go to relevant DTC chart (See page 

DI–58

).

A

–

DIAGNOSTICS

ENGINE

DI–141

335

2

Inspect thermostat (See page 

CO–12

).

CHECK:
Check the valve opening temperature of the thermostat.
OK:

Valve opening temperature is 80 to 84



C (176 to 183



F)

HINT:
Also check that the valve is completely closed under opening temperature as above.

NG

Replace thermostat (See page 

CO–11

).

OK

3

Check cooling system.

CHECK:
Check that there is detect in the cooling system which causes overcool, such as abnormal radiator fan opera-
tion, modified cooling system and so on.

NG

Repair or replace cooling system.

OK

Replace engine coolant temperature sensor.

A20488

A21045

Threshold 
(75



C (167



F))

Estimated ECT

5 sec.

Indicated coolant temp. reading

DTC set (after 2 driving cycle)

ECT

Time

DI–142

–

DIAGNOSTICS

ENGINE

336

DTC

P0128

Coolant Thermostat (Coolant Temperature
Below Thermostat Regulating Temperature)

HINT:
This is the purpose of ”thermostat” malfunction detection.

CIRCUIT DESCRIPTION

If the engine coolant temperature does not reach 75

°

C (167

°

F) despite sufficient warm–up time has

elapsed.

DTC No.

DTC Detection condition

Trouble Area

P0128

Condition (a), (b) and (c) are met:

(a) Cold start

(b) After sufficient warm–up time has elapsed

(c) Engine coolant temperature greater than 75

°

C (167

°

F)

Thermostat

Cooling system

Engine coolant temperature sensor

ECM

MONITOR DESCRIPTION

The ECM estimates the coolant temperature based on starting temperature, engine loads, and engine
speeds. The ECM then compares the estimated temperature with the actual ECT (Engine Coolant Tempera-
ture). When the estimated coolant temperature reaches 75



C (167



F), the ECM checks the actual ECT. If

the actual ECT is less than 75



C (167



F), the ECM will interpret this as a fault in the thermostat or engine

cooling system and set a DTC.

DICEQ–02