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DTC P0126:00 [PCM (SKYACTIV-G 2.0)]

NOTE:

  • To determine the malfunctioning part, proceed with the diagnostics from "Function Inspection Using M-MDS".

Details On DTCs

DESCRIPTION

Thermostat stuck open

DETECTION CONDITION

Determination conditions

  • Actual engine coolant temperature does not exceed 71 °C {160 °F} even though the estimated engine coolant temperature after the engine is started exceeds 71 °C {160 °F}.

Preconditions

  • Difference between value*2 detected by ECT sensor No.2 during malfunction determination and value detected by ECT sensor No.2 at engine start is 13 °C {23 °F} or more

  • Engine coolant temperature at engine start: 52 °C {126 °F} or less*1

  • IAT: −10—45 °C {14—113 °F}*1

  • Vehicle speed: 140 km/h {87 mph} or less*1

  • Engine speed: 5,400 rpm or less*1

  • Idle ratio: 50 % or less

  • The following DTCs are not detected:

    • Fuel system malfunction: P0171:00, P0172:00, P2096:00, P2097:00

    • ECT sensor No.1 malfunction: P0117:00, P0118:00

    • MAF sensor malfunction: P0102:00, P0103:00

  • *1: Value can be verified by displaying PIDs using M-MDS

  • *2: Uses the ECT sensor No.1 actual temperature or the estimated temperature, whichever one reaches 71 °C {160 °F} first, as the detection determination value.

Drive cycle

  • 2

Self test type

  • CMDTC self test

Sensor used

  • Desired engine coolant temperature: intake air temperature (IAT sensor), engine speed (CKP sensor), charging efficiency

  • Actual engine coolant temperature: ECT sensor No.1, ECT sensor No.2

FAIL-SAFE FUNCTION

  • Not applicable

VEHICLE STATUS WHEN DTCs ARE OUTPUT

  • Illuminates check engine light.

  • Heating is ineffective after engine is started

POSSIBLE CAUSE

  • ECT sensor No.1 malfunction

  • ECT sensor No.2 malfunction

  • Poor assembly of ECT sensor No.1

  • Poor assembly of ECT sensor No.2

  • Poor assembly of engine coolant hose (engine coolant passage malfunction)

  • Poor engine coolant, leakage, or freezing

  • Use of unspecified engine coolant

  • Foreign matter caught in thermostat (foreign matter penetration in engine coolant)

  • Thermostat malfunction

  • PCM malfunction

System Wiring Diagram

  • Not applicable

Function Explanation (DTC Detection Outline)

  • The PCM calculates the estimated engine coolant temperature according to the engine speed, charging efficiency, and intake air temperature. If the actual engine coolant temperature does not exceed 71.1 °C {160 ° F} during the malfunction determination time after the estimated engine coolant temperature exceeds 71.1 °C {160 °F}, malfunction determination for the engine coolant system is performed and a DTC is stored.

  • The malfunction determination time varies depending on the engine speed, charging efficiency, and intake air temperature.

Repeatability Verification Procedure

  • Switch the ignition off.

  • Leave the vehicle until the engine coolant temperature reaches approx. 35 °C {95 °F}.

  • Start the engine.

    NOTE:

    • Match the engine coolant temperature in the recorded FREEZE FRAME DATA/snapshot data, the vehicle speed, and engine speed values to the best extent possible while driving the vehicle.

  • Try to reproduce the malfunction by driving the vehicle for 5 min based on the values in the FREEZE FRAME DATA/snapshot data.

PID Item/Simulation Item Used In Diagnosis

PID/DATA monitor item table

Item

Definition

Unit

Condition/Specification

ECT

Engine coolant temperature input from ECT sensor No.1

°C, °F

  • Displays ECT

ECT sensor No.1 voltage

V
    Ignition switched ON (engine off)

  • ECT is 92 °C {198 °F}: Approx. 0.65 V

    Idle (after warm up)

  • ECT is 93 °C {199 °F}: Approx. 0.64 V

    Racing (Engine speed is 2,000 rpm)

  • ECT is 92 °C {198 °F}: Approx. 0.66 V

    Racing (Engine speed is 4,000 rpm)

  • ECT is 93 °C {199 °F}: Approx. 0.64 V

Function Inspection Using M-MDS

STEP

INSPECTION

RESULTS

ACTION

1

 PURPOSE: VERIFY RELATED REPAIR INFORMATION AVAILABILITY

  • Verify related Service Bulletins and/or on-line repair information availability.

  • Is any related repair information available?

Yes

Perform repair or diagnosis according to the available repair information.

  • If the vehicle is not repaired, go to the next step.

No

Go to the next step.

2

 PURPOSE: RECORD VEHICLE STATUS AT TIME OF DTC DETECTION TO UTILIZE WITH REPEATABILITY VERIFICATION

NOTE:

  • Recording can be facilitated using the screen capture function of the PC.

  • Record the FREEZE FRAME DATA/snapshot data on the repair order.

—

Go to the next step.

3

 PURPOSE: DETERMINE IF MALFUNCTION CAUSE IS ECT SENSOR NO.1 (PCM INPUT SIGNAL) OR OTHER PART

Yes

Inspect for DTC P0116:00 due to the high possibility of an ECT sensor No.1 malfunction.

(See DTC P0116:00 [PCM (SKYACTIV-G 2.0)].)

No

Go to the troubleshooting procedure to perform the procedure from Step 1.

Troubleshooting Diagnostic Procedure

    Intention of troubleshooting procedure

  • Step 1—2

    • Perform an engine coolant-related inspection.

  • Step 3

    • Perform an engine coolant passage assembly condition-related inspection.

  • Step 4

    • Perform a unit inspection of the thermostat.

  • Step 5—6

    • Perform a PCM input signal part-related inspection.

  • Step 7—8

    • Verify that the primary malfunction is resolved and there are no other malfunctions.

STEP

INSPECTION

RESULTS

ACTION

1

 PURPOSE: DETERMINE IF ENGINE COOLANT USED AFFECTS CONDITION BY VERIFYING WITH CUSTOMER AND INSPECTING COLOR, ODOR, AND FOAMING DUE TO POSSIBILITY OF ENGINE COOLANT FREEZING IF ENGINE COOLANT CONCENTRATION IS LOW

  • Is the specified engine coolant being used?

Yes

Go to the next step.

No

Replace the engine coolant, then go to Step 7. (Advise the customer to use specified engine coolant used.)

(See ENGINE COOLANT REPLACEMENT [SKYACTIV-G 2.0].)

2

 PURPOSE: VERIFY THAT THERE IS NO ENGINE COOLANT LEAKAGE OR FOREIGN MATTER PENETRATION BECAUSE ECT SENSOR MAY NOT MEASURE CORRECT TEMPERATURE DUE TO ENGINE COOLANT LEAKAGE

Yes

If there is engine coolant leakage:

  • Repair or replace the malfunctioning location and refill the system with engine coolant.

If there is foreign matter penetration:

Go to Step 7.

No

Go to the next step.

3

 PURPOSE: VERIFY IF ENGINE COOLANT PASSAGE IS CORRECT BECAUSE CORRECT ENGINE COOLANT TEMPERATURE CANNOT BE DETERMINED IF ENGINE COOLANT PASSAGE IS INCORRECT

  • Is the engine coolant passage (such as hose) connected correctly? (ask customer if engine coolant passage has been serviced somewhere other than Authorized Mazda Dealer)

Yes

Go to the next step.

No

Connect engine coolant passage correctly, then go to Step 7.

4

 PURPOSE: EXAMINE THERMOSTAT BECAUSE ENGINE COOLANT TEMPERATURE INCREASE SLOWS IF THERMOSTAT IS STUCK OPEN

Yes

Replace the thermostat, then go to Step 7.

(See THERMOSTAT REMOVAL/INSTALLATION [SKYACTIV-G 2.0].)

No

Go to the next step.

5

 PURPOSE: EXAMINE ECT SENSOR BECAUSE ENGINE COOLANT TEMPERATURE CANNOT BE MEASURED CORRECTLY IF ECT SENSOR IS MALFUNCTIONING

Yes

Replace the ECT sensor No.1 or ECT sensor No.2, then go to Step 7.

(See ENGINE COOLANT TEMPERATURE (ECT) SENSOR REMOVAL/INSTALLATION [SKYACTIV-G 2.0].)

No

Go to the next step.

6

 PURPOSE: VERIFY ASSEMBLY CONDITION BECAUSE ENGINE COOLANT TEMPERATURE CANNOT BE MEASURED CORRECTLY IF ECT SENSOR IS NOT ASSEMBLED CORRECTLY

Yes

Go to the next step.

No

Assemble the ECT sensor No.1 and ECT sensor No.2 correctly, then go to the next step.

(See ENGINE COOLANT TEMPERATURE (ECT) SENSOR REMOVAL/INSTALLATION [SKYACTIV-G 2.0].)

7

 PURPOSE: VERIFICATION OF VEHICLE REPAIR COMPLETION

Yes

Repeat the inspection from Step 1 of the troubleshooting diagnostic procedure.

Go to the next step.

No

Go to the next step.

8

 PURPOSE: VERIFY IF THERE IS ANY OTHER MALFUNCTION

  • Is any other DTC or pending code stored?

Yes

Go to the applicable DTC inspection.

(See DTC TABLE [PCM (SKYACTIV-G 2.0)].)

No

DTC troubleshooting completed.
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Free to use workshop manual for your 2015+ Mk4 'ND' Mazda MX-5

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