2UZ-FE ENGINE CONTROL SYSTEM: SFI SYSTEM: P0128; Thermostat Malfunction; 2007 MY LX470 [08/2006

Last Modified: 7-3-2017	6.8:8.0.40	Doc ID: RM000000YDV00NX
Model Year Start: 2007	Model: LX470	Prod Date Range: [08/2006 - ]
Title: 2UZ-FE ENGINE CONTROL SYSTEM: SFI SYSTEM: P0128; Thermostat Malfunction; 2007 MY LX470 [08/2006 - ]

DTC

P0128

Thermostat Malfunction

DESCRIPTION

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

DTC No.	DTC Detection Condition	Trouble Area
P0128	Conditions (a), (b) and (c) are met: (a) Cold start (b) After sufficient warm-up time has elapsed (c) ECT is less than 75°C (167°F)	Thermostat Cooling system Engine Coolant Temperature (ECT) 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. 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 engine cooling system or thermostat and set a DTC.

MONITOR STRATEGY

Related DTCs	P0128: Coolant thermostat
Required Sensors/Components (Main)	Thermostat
Required Sensors/Components (Related)	Engine coolant temperature sensor, Intake air temperature sensor, Vehicle speed sensor
Frequency of Operation	Once per drive cycle
Duration	15 minutes
MIL Operation	2 driving cycles
Sequence of Operation	None

TYPICAL ENABLING CONDITIONS

Monitor will run whenever these DTCs are 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 (Fuel system) P0300 - P0308 (Misfire) P0335 (CKP sensor) P0340 - P0346 (VVT sensor) P0351 - P0358 (igniter) P0500 (VSS) P2196, P2198 (A/F sensor - rationality) P2237, P2240 (A/F sensor - open) P2A00, P2A03 (A/F sensor - slow response)
Battery voltage	11 V or higher
One of the following conditions 1 or 2 is met	-
1. All of the following conditions (a), (b) and (c) are met	-
(a) ECT at engine start - IAT at engine start	-15 to 7°C (5 to 12.6°F)
(b) ECT at engine start	-10 to 56°C (14 to 132.8°F)
(c) IAT at engine start	-10 to 56°C (14 to 132.8°F)
2. All of the following conditions (a), (b) and (c) are met	-
(a) ECT at engine start - IAT at engine start	Higher than 7°C (12.6°F)
(b) ECT at engine start	56°C (133°F) or lower
(c) IAT at engine start	-10°C (14°F) or higher
Accumulated time that vehicle speed is 128 km/h (80 mph) or more	Less than 20 seconds

TYPICAL MALFUNCTION THRESHOLDS

Duration that all of following conditions are met	5 seconds or more
(a) Estimated ECT	75°C (167°F) or higher
(b) ECT sensor output	Lower than 75°C (167°F)

INSPECTION PROCEDURE

HINT:

Read freeze frame data using the intelligent tester. Freeze frame data records the engine conditions when malfunctions are 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, and other data from the time the malfunction occurred.

PROCEDURE

1.	CHECK OTHER DTC OUTPUT (IN ADDITION TO DTC P0128)

(a) Connect the intelligent tester to the CAN VIM. Then connect the CAN VIM to the DLC3.

(b) Turn the ignition switch ON and turn the intelligent tester ON.

(d) Read the DTC.

Result:

Display (DTC output)	Proceed to
P0128	A
P0128 and other DTCs	B

HINT:

If any other codes besides P0128 are output, perform the troubleshooting for those DTCs first.

GO TO RELEVANT DTC CHART

2.	CHECK COOLING SYSTEM

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

(b) 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 below the opening temperature shown above.

REPAIR OR REPLACE COOLING SYSTEM

3.	INSPECT THERMOSTAT

(a) Remove the thermostat .

(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.

REPLACE THERMOSTAT

REPLACE ECM