DTC    P0128    Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

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DESCRIPTION

This DTC is stored when the engine coolant temperature does not reach 75°C (167°F) despite sufficient engine warmup time having elapsed.

DTC No.
DTC Detection Condition
Trouble Area
P0128
  1. Conditions (a), (b) and (c) met and 5 seconds elapse (2 trip detection logic):
  2. (a) Engine is started cold.
  3. (b) Engine is warmed up.
  4. (c) Engine coolant temperature is below 75°C (167°F).
  1. Water inlet with thermostat
  2. Cooling system
  3. Engine coolant temperature sensor
  4. ECM

MONITOR DESCRIPTION


A121605E18

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 75°C (167°F), the ECM checks the actual engine coolant temperature. If the actual engine coolant temperature is below 75°C (167°F), the ECM interprets this as a malfunction in the thermostat or the engine cooling system and stores the DTC.

MONITOR STRATEGY


Related DTCs
P0128: Coolant Thermostat
Required Sensors/Components (Main)
Water inlet with thermostat
Required Sensors/Components (Related)
Engine coolant temperature sensor, intake air temperature sensor, vehicle speed sensor
Frequency of Operation
Once per driving cycle
Duration
900 seconds
MIL Operation
2 driving cycles
Sequence of Operation
None

TYPICAL ENABLING CONDITIONS


Monitor runs whenever following DTCs not stored
P0010, P0020 (VVT Oil Control Valve)
P0011, P0021 (VVT System - Advance)
P0012, P0022 (VVT System - Retard)
P0016, P0018 (VVT System - Misalignment)
P0013, P0023 (Exhaust VVT Oil Control Valve)
P0014, P0024 (Exhaust VVT System - Advance)
P0015, P0025 (Exhaust VVT System - Retard)
P0017, P0019 (Exhaust VVT System - Misalignment)
P0031, P0032, P0051, P0052, P101D, P103D (Air Fuel Ratio Sensor Heater)
P014C, P014D, P014E, P014F, P015A, P015B, P015C, P015D, P2195, P2196, P2197, P2198, P2237, P2238, P2239, P2240, P2241, P2242, P2252, P2253, P2255, P2256 (Air Fuel Ratio Sensor)
P0102, P0103 (Mass Air Flow Sensor)
P0112, P0113 (Intake Air Temperature Sensor)
P0115, P0117, P0118 (Engine Coolant Temperature Sensor)
P0120, P0121, P0122, P0123, P0220, P0222, P0223, P2135 (Throttle Position Sensor)
P0171, P0172, P0174, P0175 (Fuel System)
P0301 - P0306 (Misfire)
P0335 (Crankshaft Position Sensor)
P0340, P0342, P0343, P0345, P0347, P0348 (VVT Sensor)
P0365, P0367, P0368, P0390, P0392, P0393 (Exhaust VVT Sensor)
P0351 - P0356 (Igniter)
P0500 (Vehicle Speed Sensor)
P219A, P219B (Air-fuel ratio imbalance)
Battery voltage
11 V or higher
Either of following conditions 1 or 2 met:
-
1. All of following conditions met:
-
  1. Engine coolant temperature at engine start - intake air temperature at engine start
-15 to 7°C (-27 to 12.6°F)
  1. Engine coolant temperature at engine start
-10 to 56°C (14 to 133°F)
  1. Intake air temperature at engine start
-10 to 56°C (14 to 133°F)
2. All of following conditions met:
-
  1. Engine coolant temperature at engine start - intake air temperature at engine start
More than 7°C (12.6°F)
  1. Engine coolant temperature at engine start
56°C (133°F) or less
  1. Intake air temperature at engine start
-10°C (14°F) or higher
Accumulated time at vehicle speed of 128 km/h (80 mph) or more
Less than 20 seconds

TYPICAL MALFUNCTION THRESHOLDS


Duration that both of following conditions (a) and (b) met
5 seconds or more
(a) Estimated engine coolant temperature
75°C (167°F) or higher
(b) Engine coolant temperature sensor output
Below 75°C (167°F)

CONFIRMATION DRIVING PATTERN


A249245E01

  1. Stop the engine and allow it to soak.
  2. Connect the Techstream to the DLC3.
  3. Turn the ignition switch to ON and turn the Techstream on [A].
  4. Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / Coolant Temp and Intake Air.
  5. Check if "Coolant Temp" is 56°C (133°F) or less and "Intake Air" is between 0 and 35°C (32 and 95°F).
  6. Set the heater to MAX HOT with fresh air mode selected and turn the A/C off.
  7. Start the engine and drive the vehicle at 80 km/h (50 mph) for 15 minutes [B].

    HINT:
    1. Data can be captured relatively easily by using the snapshot function in the Data List.
    2. Enter the following menus: Data List / Function / Snap-shot configuration / Record time / 5 min.
    3. Data capture can be started by using the target point. For example, setting the target point to an engine speed of 4000 rpm and then racing the engine, etc. to raise the engine speed to a speed of 4000 rpm or more will cause data capture to start.
  8. After driving the vehicle at 80 km/h (50 mph) and "Coolant Temp" stabilizes, check that "Coolant Temp" is 75°C (167°F) or higher [C].

    HINT:
    If "Coolant Temp" is below 75°C (167°F) while driving the vehicle at 80 km/h (50 mph), inspect the cooling system and thermostat.

INSPECTION PROCEDURE

HINT:
  1. When the DTC is output, check the engine coolant temperature using the Techstream. Enter the following menus: Powertrain / Engine and ECT / Data List / 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.
  2. 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 FOR ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0128)
  1. Connect the Techstream to the DLC3.

  1. Turn the ignition switch to ON.

  1. Turn the Techstream on.

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

  1. Read the DTCs.

    Result 
    Result
    Proceed to
    P0128 is output
    A
    P0128 and other DTCs are output
    B

    HINT:
    If any DTCs other than P0128 are output, troubleshoot those DTCs first.


B
GO TO DTC CHART (Click here)
A


2.CHECK COOLING SYSTEM
  1. 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


3.INSPECT WATER INLET WITH THERMOSTAT
  1. Remove the water inlet with thermostat (Click here).

  1. Measure the valve opening temperature of the thermostat.

    Standard value:
    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.
  1. Reinstall the water inlet with thermostat (Click here).



NG
REPLACE WATER INLET WITH THERMOSTAT (Click here)
OK

REPLACE ECM (Click here)