Safety Warning

DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.

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HOMESERVICE MANUALSKIA2015FORTE LX, AUTOMATIC TRANSREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCETESTING & DIAGNOSISENGINE CONTROL SYSTEM DIAGNOSIS (1 OF 2) - 1.8LDTC P0128: COOLANT THERMOSTAT (COOLANT TEMPERATURE BELOW THERMOSTAT AT REGULATING TEMPERATURE)DTC INSPECTIONMONITOR GDS DATA

2015 Kia Forte LX, Automatic Trans

Monitor GDS Data

2015 Kia Forte LX, Automatic TransSECTION Monitor GDS Data

Allow the engine to cool completely.
Run the cold engine at idle for 5 minutes and observe cooling fan status.
NOTE: Ensure that the A/C is OFF.
Check the engine coolant temperature parameter at idle with the GDS.
Is the engine coolant temperature increase to above 50°C (122°F)
YES
- Go to "TERMINAL AND CONNECTOR INSPECTION " procedure.
NO
- Go to next step as below.
Are the cooling fans running when engine coolant temperature is low (less than approximately 98°C (208°F)) with A/C OFF?
YES
- Check for short circuit in cooling fan harness or cooling fan relay. Repair as necessary and go to "VERIFICATION OF VEHICLE REPAIR " procedure.
NO
- - With ignition "ON", Install scantool and select "COOLING FAN RELAY" on the Actuation Test mode.
  - Activates "COOLING FAN RELAY" by click "Start" button.
  - Repeat this procedure 4 or 5 times to ensure cooling fan reliability.
  - If cooling fan works properly, go to next step as below.
  - If NG, check for intermittent fault caused by poor contact in the sensor's and/or PCM/ECM's connector. Repair as necessary and go to "VERIFICATION OF VEHICLE REPAIR " procedure.

RENDER: 1.0x

NO RELATED

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.
• Brakes feel soft, pull hard to one side, or make grinding noises.
• The engine overheats, stalls repeatedly, or misfires under load.
• You are missing required tools, torque specs, or safe lifting equipment.
• You are not confident in the next step or safety outcome.