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DTC Description
 
 
DTC DETECTION LOGIC
Engine coolant temperature has not risen enough to open the thermostat even though the engine has run long enough.
This is due to a leak in the seal or the thermostat being stuck open.
DTCM.U.T.-III SE screen terms
(Trouble diagnosis content)
DTC detection condition
P012800THERMSTAT FNCTN
[Coolant thermostat (coolant temperature below thermostat regulating temperature)]
Diagnosis condition—
Signal (terminal)Engine coolant temperature sensor signal
ThresholdThe engine coolant temperature does not reach to specified temperature even though the engine has run long enough.
Diagnosis delay time—
 
 
POSSIBLE CAUSE
  • Thermostat
  • Leakage from sealing portion of thermostat
  • Engine coolant temperature sensor
 
 
FAIL-SAFE
Not applicable
 
 
DTC Confirmation Procedure
noteNever refuel before and during the following procedure.
1.CHECK DTC PRIORITY
If DTC P0128 is displayed with other DTC, first perform the trouble diagnosis for other DTC.
Is applicable DTC detected?
Perform diagnosis of applicable. Refer to DTC Index.
.
 
2.PRECONDITIONING-1
If DTC Confirmation Procedure has been previously conducted, always perform the following procedure before conducting the next test.
  1. Turn ignition switch OFF and wait at least 10 seconds.
  2. Turn ignition switch ON.
  3. Turn ignition switch OFF and wait at least 10 seconds.
: .
 
3.PRECONDITIONING-2
With M.U.T.-III SE
  1. Turn ignition switch ON.
  2. Check the following conditions:
    Ambient temperature−10°C (14°F) or more
    A/C switchOFF
    Blower fan switchOFF
  3. Select “DATA MONITOR” mode of “ENGINE” using M.U.T.-III SE.
  4. Check the following conditions:
    COOLANT TEMP/S−10°C – 58°C (14 – 136°F)
Is the condition satisfied?
.
  1. Satisfy the condition.
  2. .
 
4.PERFORM DTC CONFIRMATION PROCEDURE-1
With M.U.T.-III SE
  1. Start engine.
  2. Drive the vehicle until the following condition is satisfied.
    cautionAlways drive vehicle at safe speed.
    1. STEP 1
      Drive the vehicle under the conditions instructed below until the difference between “COOLANT TEMP/S” and “FUEL T/TMP SE” becomes at least 26°C (47°F).
      COOLANT TEMP/S66°C (151°F) or less
      FUEL T/TMP SELess than the value calculated by subtracting 26°C (47°F) from “COOLANT TEMP/S”.*
      *: Example
      COOLANT TEMP/SFUEL T/TMP SE
      70°C (158°F)44°C (111°F) or less
      65°C (149°F)39°C (102°F) or less
      60°C (140°F)34°C (93°F) or less
    2. STEP 2
      Drive the vehicle at 50 km/h (32 MPH) or more with the difference between “COOLANT TEMP/S” and “FUEL T/TMP SE” maintained at 26°C (47°F) or more.
      noteKeep the accelerator pedal as steady as possible during cruising.
    3. STEP 3
      Drive the vehicle at 50 km/h (32 MPH) or more until “COOLANT TEMP/S” increases by 6°C (11°F).
      noteKeep the accelerator pedal as steady as possible during cruising.
Is the condition satisfied?
.
.
 
5.PERFORM DTC CONFIRMATION PROCEDURE-2
With M.U.T.-III SE
  1. Drive the vehicle until the following condition is satisfied.
    COOLANT TEMP/S67°C (153°F) or more
    cautionAlways drive vehicle at safe speed.
  2. Check 1st trip DTC.
Is 1st trip DTC detected?
Proceed to DTC Diagnosis Procedure.
-1To check malfunction symptom before repair: Refer to Intermittent IncidentIntermittent Incident.
-2Confirmation after repair: INSPECTION END