Lexus NX: Thermostat (P0128)
DESCRIPTION
This DTC is stored when the engine coolant temperature does not reach 73°C (163°F) despite sufficient engine warm-up time having elapsed.
| DTC No. | Detection Item | DTC Detection Condition | Trouble Area | MIL | Memory |
|---|---|---|---|---|---|
| P0128 | Thermostat | All of the following conditions are met for 5 seconds (2 trip detection logic): (a) Cold start (b) The engine is warmed up (c) The engine coolant temperature is less than 73°C (163°F) |
| Comes on | DTC stored |
MONITOR DESCRIPTION
The ECM estimates the engine coolant temperature based on the starting temperature, engine load, and engine speed. The ECM then compares the estimated temperature with the actual engine coolant temperature. When the estimated engine coolant temperature reaches 73°C (163°F), the ECM checks the actual engine coolant temperature. If the actual engine coolant temperature is less than 73°C (163°F), the ECM interprets this as a malfunction in the thermostat or the engine cooling system and stores this DTC.
MONITOR STRATEGY
| Related DTCs | P0128: Coolant thermostat |
| Required Sensors/Components (Main) | Thermostat Engine coolant temperature sensor |
| Required Sensors/Components (Related) | Intake air temperature sensor |
| Frequency of Operation | Once per driving cycle |
| Duration | 560 seconds |
| MIL Operation | 2 driving cycles |
| Sequence of Operation | None |
TYPICAL ENABLING CONDITIONS
| Monitor runs whenever the following DTCs are not stored | P0010 (Camshaft timing oil control valve) P0011 (VVT system - advance) P0012 (VVT system - retard) P0016 (VVT system - misalignment) P0031, P0032, P101D (Air fuel ratio sensor heater) P0102, P0103 (Mass air flow meter) P0107, P0108 (Manifold absolute pressure) P0112, P0113 (Intake air temperature sensor) P0115, P0117, P0118 (Engine coolant temperature sensor) P0120, P0121, P0122, P0123, P0220, P0222, P0223, P2135 (Throttle position sensor) P014C, P014D, P015A, P015B, P2195, P2196, P2237, P2238, P2239, P2252, P2253 (Air fuel ratio sensor) P0171, P0172 (Fuel system) P0300, P0301, P0302, P0303, P0304 (Misfire) P0335 (Crankshaft position sensor) P0340 (Camshaft position sensor) P0340, P0342, P0343 (VVT sensor) P0351, P0352, P0353, P0354 (Igniter) P0401 (EGR system) P219A, P219C, P219D, P219E, P219F (Air-fuel ratio imbalance) |
| Auxiliary battery voltage | 11 V or higher |
| Either of the following conditions is met | 1 or 2 |
| 1. All of the following conditions are met | - |
| Engine coolant temperature at engine start - Intake air temperature at engine start | -15 to 7°C (-27 to 12.6°F) |
| Engine coolant temperature at engine start | -10 to 56°C (14 to 133°F) |
| Intake air temperature at engine start | -10 to 56°C (14 to 133°F) |
| 2. All of the following conditions are met | - |
| Engine coolant temperature at engine start - Intake air temperature at engine start | Higher than 7°C (12.6°F) |
| Engine coolant temperature at engine start | 56°C (133°F) or less |
| Intake air temperature 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 the following conditions are met | 5 seconds or more |
| Estimated engine coolant temperature | 73°C (163°F) or higher |
| Engine coolant temperature sensor output | Less than 73°C (163°F) |
CONFIRMATION DRIVING PATTERN
- Stop the engine and allow it to soak.
- Connect the Techstream to the DLC3.
- Turn the power switch on (IG) and turn the Techstream on [A].
- Enter the following menus: Powertrain / Engine and ECT / Data List / Primary / Coolant Temp and Intake Air.
- Check that "Coolant Temp" is 56°C (133°F) or less and "Intake Air" is between 0 and 35°C (32 and 95°F).
-
Put the engine in inspection mode (maintenance mode).
Click here
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- Set the heater to MAX HOT with fresh air mode selected and turn the A/C off.
- Start the engine.
-
With the engine running, drive the vehicle at 80 km/h (50 mph) for 15 minutes [B].
CAUTION:
When performing the confirmation driving pattern, obey all speed limits and traffic laws.
HINT:
If the engine stops, further depress the accelerator pedal to restart the engine.
-
After "Coolant Temp" stabilizes, check that "Coolant Temp" is 73°C (163°F) or higher [C].
HINT:
If "Coolant Temp" is less than 73°C (163°F) while driving the vehicle at 80 km/h (50 mph), inspect the cooling system and thermostat.
CAUTION / NOTICE / HINT
HINT:
- When the DTC is output, check the engine coolant temperature using the Techstream. Enter the following menus: Powertrain / Engine and ECT / Data List / Primary / Coolant Temp. If the Coolant Temp value is lower than the actual engine coolant temperature, the engine coolant temperature sensor circuit may be malfunctioning. In this case, check the wire harnesses and connectors (and those connections) between the ECM and the engine coolant temperature sensor 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 P0128) |
(a) Connect the Techstream to the DLC3.
(b) Turn the power switch on (IG).
(c) Turn the Techstream on.
(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 P0128 is output | A |
| DTC P0128 and other DTCs are output | B |
HINT:
If any DTCs other than P0128 are output, troubleshoot those DTCs first.
| B | .gif) | GO TO DTC CHART |
|
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| 2. | 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.
| NG | | REPAIR OR REPLACE COOLING SYSTEM |
|
| 3. | INSPECT THERMOSTAT |
(a) Inspect the thermostat (thermostat opening temperature).
Click here
| NG | | REPLACE THERMOSTAT |
|
| 4. | INSPECT ENGINE COOLANT TEMPERATURE SENSOR |
(a) Inspect the engine coolant temperature sensor.
Click here
HINT:
Perform "Inspection After Repair" after replacing the engine coolant temperature sensor.
Click here
| OK | | REPLACE ECM |
| NG | | REPLACE ENGINE COOLANT TEMPERATURE SENSOR |
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