SFI SYSTEM, Diagnostic DTC:P0128

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

DESCRIPTION

Tech Tips

This DTC relates to the thermostat.

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

DTC No. DTC Detection Condition Trouble Area
P0128

  • 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 75°C (167°F).

  • Thermostat

  • Cooling system

  • Engine coolant temperature sensor

  • ECM

MONITOR DESCRIPTION

A011V4EE23

The ECM estimates the engine coolant temperature based on the starting temperature, engine loads, and engine speeds. 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 less than 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)

Thermostat

Engine coolant temperature sensor
Required Sensors/Components (Related)

Intake air temperature sensor

Vehicle speed sensor
Frequency of Operation Once per driving cycle
Duration 700 seconds
MIL Operation 2 driving cycles
Sequence of Operation None

TYPICAL ENABLING CONDITIONS

Monitor runs whenever the following DTCs are not stored

P0010 (VVT oil control valve)

P0011 (VVT system - advance)

P0012 (VVT system - retard)

P0016 (VVT system - misalignment)

P0013 (Exhaust VVT oil control valve)

P0014 (Exhaust VVT system - advance)

P0015 (Exhaust VVT system - retard)

P0017 (Exhaust VVT system - misalignment)

P0031, P0032, P0101D (Air fuel ratio sensor heater)

P0102, P0103 (Mass air flow meter)

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 (Fuel system)

P0301 - P0304 (Misfire)

P0335 (Crankshaft position sensor)

P0340, P0342, P0343 (Camshaft position sensor)

P0365, P0367, P0368 (Exhaust camshaft position sensor)

P0351 - P0354 (Igniter)

P0500 (Vehicle speed sensor)

P014C, P014D, P015A, P015B, P2195, P2196, P2237, P2238, P2239, P2252, P2253, P2A00 (Air fuel ratio sensor)

P219A (Air fuel ratio imbalance)
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 both of following conditions met 5 seconds or more
(a) Estimated engine coolant temperature 75°C (167°F) or higher
(b) Engine coolant temperature sensor output Less than 75°C (167°F)

CONFIRMATION DRIVING PATTERN

A011UYPE01

  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 / Primary / Coolant Temp and Intake Air.

  5. Check that "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].

    CAUTION:

    When performing the confirmation driving pattern, obey all speed limits and traffic laws.

    Tech Tips

    • Data can be captured relatively easily by using the snapshot function in the Data List.

    • Enter the following menus: Data List / Function / Snapshot Configure / Duration / 5 min.

    • Data capture can be started by using the target point function. 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 higher will cause data capture to start.

  8. After "Coolant Temp" stabilizes, check that "Coolant Temp" is 75°C (167°F) or higher [C].

    Tech Tips

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

INSPECTION PROCEDURE

Tech Tips

  • 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.

  • 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.

PROCEDURE

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

    1. Connect the Techstream to the DLC3.

    2. Turn the ignition switch to ON.

    3. Turn the Techstream on.

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

    5. Read the DTCs.

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

      Tech Tips

      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 cooling fan operation or any modifications.

    NG

    REPAIR OR REPLACE COOLING SYSTEM

    OK

  3. INSPECT THERMOSTAT

    1. Inspect the thermostat opening temperature Click here.

    NG

    REPLACE THERMOSTAT Click here

    OK

    REPLACE ECM Click here