Toyota Tundra. Manual — part 1174

TYPICAL MALFUNCTION THRESHOLDS

FAIL-SAFE

When this DTC, as well as other DTCs relating to ETCS (Electronic Throttle Control System) malfunctions, is
set, the ECM enters fail-safe mode. During fail-safe mode, the ECM cuts the current to the throttle actuator, and
the throttle valve is returned to a 6° throttle angle by the return spring. The ECM then adjusts the engine output
by controlling the fuel injection (intermittent fuel-cut) and ignition timing, in accordance with the accelerator
pedal opening angle, to allow the vehicle to continue at a minimal speed. If the accelerator pedal is depressed
firmly and gently, the vehicle can be driven slowly.

Fail-safe mode continues until a pass condition is detected, and the ignition switch is then turned OFF.

INSPECTION PROCEDURE

HINT:



This DTC relates to the Throttle Position (TP) sensor.



Read freeze frame data using the Techstream. Freeze frame data records 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.

1. CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0121)

a. Connect the Techstream to the DLC3.

b. Turn the ignition switch ON.

c. Turn the Techstream ON.

d. Enter the following menus: Powertrain/Engine and ECT/Trouble Codes.

e. Read DTCs.

Result

RESULT CHART

B : GO TO DTC CHART (See DIAGNOSTIC TROUBLE CODE CHART )

A : REPLACE THROTTLE BODY ASSEMBLY (See REMOVAL )

DTC P0125 INSUFFICIENT COOLANT TEMPERATURE FOR CLOSED LOOP FUEL CONTROL

Either of following conditions set

-

Difference of TP sensor voltage between VTA1 and VTA2 x 0.8

Higher than 1.6 V

Difference of TP sensor voltage between VTA1 and VTA2 x 0.8

Lower than 0.8 V

Display (DTC output) Proceed To

P0121

A

P0121 and other DTCs

B

2008 Toyota Tundra

2008 ENGINE PERFORMANCE Engine Control System (1GR-FE) - Tundra

DESCRIPTION

Refer to DTC P0115 .

DTC TROUBLE DETECTION CONDITION CHART

MONITOR DESCRIPTION

The resistance of the ECT sensor varies in proportion to the actual ECT. The ECM supplies a constant voltage
to the sensor and monitors the signal output voltage of the sensor. The signal output voltage varies according to
the changing resistance of the sensor. After the engine is started, the ECT is monitored through this signal. If the
ECT sensor indicates that the engine is not yet warm enough for closed-loop fuel control, despite a specified
period of time having elapsed since the engine was started, the ECM interprets this as a malfunction in the
sensor or cooling system and sets the DTC.

Example:

The ECT is 0°C (32°F) at engine start. After about 1 minute running time, the ECT sensor still indicates that the
engine is not warm enough to begin closed-loop fuel (air-fuel ratio feedback) control. The ECM interprets this
as a malfunction in the sensor or cooling system and sets the DTC.

MONITOR STRATEGY

MONITOR STRATEGY

DTC

No.

DTC Detection Condition

Trouble Area

P0125

Engine coolant temperature (ECT) does not reach closed-loop
enabling temperature for 20 minutes (this period varies with engine
start ECT) (2 trip detection logic)



Cooling system



Engine coolant
temperature sensor



Thermostat

Related DTCs

P0125: Insufficient engine coolant temperature for closed-loop fuel
control

Required Sensors/Components
(Main)

Engine coolant temperature sensor, thermostat, cooling system

Required Sensors/Components
(Related)

-

Frequency of Operation

Once per driving cycle

Duration

58 seconds: Engine coolant temperature at engine start -3.3°C (26°
F) or more
105 seconds: Engine coolant temperature at engine start -14.5 to -
3.3°C (5.9 to 26°F)
1200 seconds: Engine coolant temperature at engine start -14.5°C
(5.9°F)

MIL Operation

2 driving cycles

Sequence of Operation

None

2008 Toyota Tundra

2008 ENGINE PERFORMANCE Engine Control System (1GR-FE) - Tundra

TYPICAL ENABLING CONDITIONS

TYPICAL ENABLING CONDITIONS

TYPICAL MALFUNCTION THRESHOLDS

TYPICAL MALFUNCTION THRESHOLDS

WIRING DIAGRAM

Refer to DTC P0115 .

INSPECTION PROCEDURE

HINT:



If any of DTCs P0115, P0116, P0117 or P0118 are set simultaneously with DTC P0125, the Engine
Coolant Temperature (ECT) sensor may have an open or a short circuit. Troubleshoot those DTCs first.



Read freeze frame data using the Techstream. Freeze frame data records 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.

1. CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0125)

a. Connect the Techstream to the DLC3.

b. Turn the ignition switch ON.

c. Turn the Techstream ON.

d. Enter the following menus: Powertrain/Engine and ECT/Trouble Codes.

e. Read DTCs.

Result

RESULT CHART

Monitor runs whenever following DTCs not present

P0102 - P0103 (MAF meter)
P0110 - P0113 (IAT sensor)
P0115 - P0118 (ECT sensor)

Thermostat fail

Not detected

Time until actual engine coolant temperature reaches
closed-loop fuel control enabling temperature

58 seconds: Engine coolant temperature at
engine start -3.3°C (26°F) or more
105 seconds: Engine coolant temperature at
engine start -14.5 to -3.3°C (5.9 to 26°F)
1200 seconds: Engine coolant temperature at
engine start -14.5°C (5.9°F)

Display (DTC Output) Proceed To

P0125

A

2008 Toyota Tundra

2008 ENGINE PERFORMANCE Engine Control System (1GR-FE) - Tundra

HINT:

If any DTCs other than P0125 are output, troubleshoot those DTCs first.

B : GO TO DTC CHART (See DIAGNOSTIC TROUBLE CODE CHART )

A : Go to next step

2. INSPECT WATER INLET WITH THERMOSTAT (THERMOSTAT)

a. Remove the water inlet with thermostat. (See REMOVAL ).

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 INSTALLATION ).

NG : REPLACE WATER INLET WITH THERMOSTAT . (See INSTALLATION ).

OK : Go to next step

3. CHECK COOLING SYSTEM

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 : REPAIR OR REPLACE COOLING SYSTEM

OK : REPLACE ENGINE COOLANT TEMPERATURE SENSOR (See REMOVAL )

DTC P0128 COOLANT THERMOSTAT (COOLANT TEMPERATURE BELOW THERMOSTAT
REGULATING TEMPERATURE)

DESCRIPTION

This DTC is set when the Engine Coolant Temperature (ECT) does not reach 75°C (167°F) despite sufficient
engine warm-up time having elapsed.

DTC TROUBLE DETECTION CONDITION CHART

P0125 and other DTCs

B

2008 Toyota Tundra

2008 ENGINE PERFORMANCE Engine Control System (1GR-FE) - Tundra