SFI SYSTEM, Diagnostic DTC:P0128

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

DESCRIPTION

This DTC is set when the engine coolant temperature 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 for 5 seconds

(2 trip detection logic):

(a) Cold start

(b) Engine warmed up

(c) Engine coolant temperature less than 75°C (167°F)

  • Water inlet with thermostat

  • Cooling system

  • Engine coolant temperature sensor

  • ECM

MONITOR DESCRIPTION

B002BLRE24

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 sets the DTC.

MONITOR STRATEGY

Frequency of Operation Once per driving cycle

CONFIRMATION DRIVING PATTERN

B002BOEE15

  1. Stop the engine and allow it to soak.

  2. Connect the GTS to the DLC3.

  3. Turn the power switch on (IG) and turn the GTS on [A].

  4. Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / 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 (0 and 95°F).

  6. Put the engine in inspection mode (maintenance mode) Click here.

  7. Set the heater to MAX HOT with fresh air mode selected and turn the A/C off.

  8. 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.

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

    Tech Tips

    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.

CAUTION / NOTICE / HINT

Tech Tips


  • Read freeze frame data using the GTS. 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 GTS. 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 GTS to the DLC3.

    2. Turn the power switch on (IG).

    3. Turn the GTS 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 radiator fan operation or any modifications.


    NG

    REPAIR OR REPLACE COOLING SYSTEM

    OK

  3. INSPECT WATER INLET WITH THERMOSTAT


    1. Inspect the water inlet with thermostat Click here.


    OK

    REPLACE ECM Click here

    NG

    REPLACE WATER INLET WITH THERMOSTAT Click here