P0128 on HYUNDAI ELANTRA — Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

Q: "What does P0128 mean on a HYUNDAI ELANTRA?"

"P0128 indicates: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature). This is a fuel and air metering code. 2 HYUNDAI ELANTRA owners have reported this to NHTSA."

Q: "What are the most common causes of P0128 on HYUNDAI ELANTRA?"

"Based on 2 NHTSA reports, the most commonly cited components are: Engine, Electrical System,Engine,Fuel/Propulsion System. These percentages are based on the component field in owner complaints."

Q: "Is P0128 a safety concern on HYUNDAI ELANTRA?"

"Of 2 NHTSA reports for P0128 on HYUNDAI ELANTRA, 1 involved a crash. Always consult a qualified mechanic for any diagnostic trouble code."

Q: "What should I do if my HYUNDAI ELANTRA shows P0128?"

"1) Check for recalls on your VIN at nhtsa.gov/recalls. 2) Get a professional diagnosis — a code alone doesn't identify the exact failed part. 3) Get 2-3 repair estimates to compare."

What P0128 Means on Your HYUNDAI ELANTRA

P0128 is a diagnostic trouble code indicating: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature). This code relates to the fuel and air metering system. The vehicle's computer detected a condition outside normal operating parameters and stored this code.

2 HYUNDAI ELANTRA owners have reported this issue to NHTSA across model years 2017-2018. Most reports come from the 2017, 2018 model years. The most commonly reported component is Engine (50.0% of reports).

Real HYUNDAI ELANTRA Owner Reports

Source: NHTSA Complaints Database

"Check engine light came on while driving to dealership for an unrelated recall on door handle. A diagnosis of the car computer showed a code of P0128 Coolant Thermostat."

— 2017 HYUNDAI ELANTRA owner · ENGINE · Filed 12/07/2021

"Initial Fault Code: P0303 Replaced all 4 spark plugs and all 4 ignition coils. The check engine light extinguished momentarily but returned, logging P0303 and a new P0301 Replaced all 4 fuel injectors. CEL extinguished momentarily and then returned, logging P0303."

— 2018 HYUNDAI ELANTRA owner · ELECTRICAL SYSTEM,ENGINE,FUEL/PROPULSION SYSTEM · Filed 04/01/2025 ⚠️ Crash reported

All reports filed by vehicle owners directly with the U.S. Department of Transportation.

📊 Complaint Trend by Model Year

1

'17

1

'18

Common Causes on HYUNDAI ELANTRA

Based on NHTSA complaint component analysis for this vehicle.

ENGINE 50%

ELECTRICAL SYSTEM,ENGINE,FUEL/PROPULSION SYSTEM 50%

What To Do Next

1
Check for recalls on YOUR VIN
Go to nhtsa.gov/recalls and enter your VIN. If your vehicle is covered, repairs are free.
2
Get a proper diagnosis
A code alone doesn't tell you the exact failed part. A diagnostic at a shop ($50–$150) pinpoints the root cause before you spend money on parts.
3
Compare repair quotes
Get 2–3 quotes. Dealer vs. independent shop prices often differ 30–50% for the same repair.

Frequently Asked Questions

What does P0128 mean on a HYUNDAI ELANTRA? ▾

P0128 indicates: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature). This is a fuel and air metering code. 2 HYUNDAI ELANTRA owners have reported this to NHTSA.

What are the most common causes of P0128 on HYUNDAI ELANTRA? ▾

Based on 2 NHTSA reports, the most commonly cited components are: Engine, Electrical System,Engine,Fuel/Propulsion System. These percentages are based on the component field in owner complaints.

Is P0128 a safety concern on HYUNDAI ELANTRA? ▾

Of 2 NHTSA reports for P0128 on HYUNDAI ELANTRA, 1 involved a crash. Always consult a qualified mechanic for any diagnostic trouble code.

What should I do if my HYUNDAI ELANTRA shows P0128? ▾

1) Check for recalls on your VIN at nhtsa.gov/recalls. 2) Get a professional diagnosis — a code alone doesn't identify the exact failed part. 3) Get 2-3 repair estimates to compare.