Lexus NX: Insufficient Coolant Temperature for Closed Loop Fuel Control (P0125)

Lexus NX Service Manual / Engine & Hybrid System / 2ar-fxe (engine Control) / Sfi System / Insufficient Coolant Temperature for Closed Loop Fuel Control (P0125)

DESCRIPTION

Refer to DTC P0115.

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DTC No.	Detection Item	DTC Detection Condition	Trouble Area	MIL	Memory
P0125	Insufficient Coolant Temperature for Closed Loop Fuel Control	The engine coolant temperature does not reach the closed loop enabling temperature for 20 minutes (this period varies with the engine coolant temperature at engine start) (2 trip detection logic).	Cooling system Engine coolant temperature sensor Thermostat	Comes on	DTC stored

MONITOR DESCRIPTION

The resistance of the engine coolant temperature sensor varies in proportion to the actual engine coolant temperature. 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 engine coolant temperature is monitored by this signal. If the engine coolant temperature 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 stores this DTC.

MONITOR STRATEGY

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	76 seconds: Engine coolant temperature at engine start is [closed-loop engine coolant temperature - 8.33°C (15°F)] or higher 166 seconds: Engine coolant temperature at engine start is [closed-loop engine coolant temperature - 19.44°C (35°F)] or higher, and less than [closed-loop engine coolant temperature - 8.33°C (15°F)] 1200 seconds: Engine coolant temperature at engine start is less than [closed-loop engine coolant temperature - 19.44°C (35°F)]
MIL Operation	2 driving cycles
Sequence of Operation	None

TYPICAL ENABLING CONDITIONS

Monitor runs whenever the following DTCs are not stored	None
All of the following conditions are met	-
Thermostat fail (P0128)	Not detected
Intake air temperature sensor circuit fail (P0112, P0113)	Not detected
Engine coolant temperature sensor circuit fail (P0115, P0117, P0118)	Not detected
Mass air flow meter circuit fail (P0101, P0102, P0103)	Not detected

TYPICAL MALFUNCTION THRESHOLDS

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

76 seconds: Engine coolant temperature at engine start is [closed-loop engine coolant temperature - 8.33°C (15°F)] or higher

166 seconds: Engine coolant temperature at engine start is [closed-loop engine coolant temperature - 19.44°C (35°F)] or higher, and less than [closed-loop engine coolant temperature - 8.33°C (15°F)]

1200 seconds: Engine coolant temperature at engine start is less than [closed-loop engine coolant temperature - 19.44°C (35°F)]

CONFIRMATION DRIVING PATTERN

Leave the vehicle outside overnight.
Connect the Techstream to the DLC3.
Turn the power switch on (IG) and turn the Techstream on.
Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
Read the DTC and record the freeze frame data.
Clear the DTCs (even if no DTCs are stored, perform the clear DTC procedure).
Enter the following menus: Powertrain / Engine and ECT / Data List / Coolant Temp.
Check that the Coolant Temp is the same or less than Initial Engine Coolant Temp in the freeze frame data.
Turn the power switch off and wait for at least 30 seconds.
Turn the power switch on (IG) and turn the Techstream on.
Put the engine in inspection mode (maintenance mode).
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Start the engine.
Wait 21 minutes or more.
Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.
Read the pending DTCs.
HINT:
- If a pending DTC is output, the system is malfunctioning.
- If a pending DTC is not output, perform the following procedure.
Enter the following menus: Powertrain / Engine and ECT / Utility / All Readiness.
Input the DTC: P0125.

Check the DTC judgment result.

Techstream Display	Description
NORMAL	DTC judgment completed System normal
ABNORMAL	DTC judgment completed System abnormal
INCOMPLETE	DTC judgment not completed Perform driving pattern after confirming DTC enabling conditions
N/A	Unable to perform DTC judgment Number of DTCs which do not fulfill DTC preconditions has reached ECU memory limit

HINT:

If the judgment result shows NORMAL, the system is normal.
If the judgment result shows ABNORMAL, the system has a malfunction.

If the judgment result is INCOMPLETE or N/A and no pending DTC is output, perform a universal trip and check for permanent DTCs.
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HINT:
- If a permanent DTC is output, the system is malfunctioning.
- If no permanent DTC is output, the system is normal.

WIRING DIAGRAM

Refer to DTC P0115.

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CAUTION / NOTICE / HINT

HINT:

If any of DTCs P0115, P0116, P0117 or P0118 are output simultaneously with DTC P0125, the engine coolant temperature sensor may have an open or a short circuit. Troubleshoot those DTCs first.
Read freeze frame data using the Techstream. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. 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.

PROCEDURE

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

(a) Connect the Techstream to the DLC3.

(b) Turn the power switch on (IG).

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

(e) Read the DTCs.

Powertrain > Engine and ECT > Trouble Codes

Result	Proceed to
DTC P0125 is output	A
DTC P0125 and other DTCs are output	B

HINT:

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

GO TO DTC CHART

2.	INSPECT THERMOSTAT

(a) Inspect the thermostat (thermostat opening temperature).

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REPLACE THERMOSTAT

3.	CHECK COOLING SYSTEM

(a) Check for defects in the cooling system that might cause the system to be too cold, such as abnormal cooling fan operation or any modifications.

HINT:

Perform "Inspection After Repair" after replacing the engine coolant temperature sensor.

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REPLACE ENGINE COOLANT TEMPERATURE SENSOR

REPAIR OR REPLACE COOLING SYSTEM

SEE MORE:

Inspection

INSPECTION PROCEDURE 1. CHECK BRAKE CYLINDER AND PISTON (a) Check the cylinder bore and piston for rust or scoring. If necessary, replace the disc brake cylinder and piston. 2. CHECK PAD LINING THICKNESS (a) Using a ruler, measure the pad lining thickness. Standard thickness: 10.0 mm (0.394 in.) Mi

GVIF Disconnected (from Park Assist/Monitoring ECU to EMV/MM Integrated Device) (B1574)

DESCRIPTION DTC No. Detection Item DTC Detection Condition Trouble Area B1574 GVIF Disconnected (from Park Assist/Monitoring ECU to EMV/MM Integrated Device) GVIF disconnected (from parking assist ECU to multi-display assembly) Harness or connector (GVIF cable) Multi-display

Lexus NX: Insufficient Coolant Temperature for Closed Loop Fuel Control (P0125)

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Thermostat (P0128)

Oxygen Sensor Circuit (Bank 1 Sensor 2) (P0136-P0139,P013A)

A/F Sensor Slow Response - Rich to Lean Bank 1 Sensor 1 (P014C,P014D,P015A,P015B)

SEE MORE:

Inspection

GVIF Disconnected (from Park Assist/Monitoring ECU to EMV/MM Integrated Device) (B1574)