P0128 on Hyundai vehicles The engine is not reaching its normal operating temperature in the expected time — usually the thermostat

A model year is listed because the code is named in its own record — a bulletin filed against it, or an owner’s complaint about it — not because every one of these vehicles sets it. Counts are documents in NHTSA’s files, not failure rates.

Owners’ own words, scrubbed of anything identifying. Unverified reports filed with NHTSA — what was said, not a finding that it was true.

Bulletins and campaigns Hyundai filed with NHTSA whose summary names P0128. Quote the document number at the service desk — it is a diagnosis the maker has already written down.

• 19-01-016H Service bulletin
  2019-04-30 · Engine And Engine Cooling
• This bulletin provides information related to an ECM (Engine Control Module) software update for DTC P0128: Coolant Thermostat (Coolant Temp below Thermostat Regulating Temperature) logic revision.
• 10160156 Service bulletin
  2019-04-30 · Engine And Engine Cooling
• Hyundai has launched a Service Campaign to update the ECM (Engine Control Module) software for DTC P0128: Coolant Thermostat (Coolant Temp below Thermostat Regulating Temperature) logic improvement.
• Campaign T3T Dea Service bulletin
  2019-11-15 · Electrical System — Software
• Hyundai has launched a Service Campaign to update the ECM (Engine Control Module) software for DTC P0128: Coolant Thermostat (Coolant Temp below Thermostat Regulating Temperature) logic improvement.
• 20-01-049H Service bulletin
  2020-12-16 · Engine And Engine Cooling
• This bulletin provides information related to the Engine Control Module (ECM) software update for OBD communication test logic, and for DTC P0128 “Coolant thermostat - Coolant temp Below thermostat regulating Temperature”. There are no drivability related conditions.
• 20-FL-012H Service bulletin
  2020-12-16 · Equipment
• This bulletin provides information related to the Engine Control Module (ECM) software logic update for DTC P0128 “Coolant thermostat - Coolant temp Below thermostat regulating Temperature”. There is no drivability issue with this DTC.
• 5NP-B6N5A-04 Service bulletin
  2017-03-16 · Power Train — Automatic Transmission
• This bulletin provides the procedure to update both the ECM (Engine Control Module) and the TCM (Transmission Control Module) on some 2016 and 2017 Hyundai Tucsons equipped with a 7-speed EcoShift® Dual Clutch Transmission (DCT). The update will address: ? A slight hesitation at low speeds that can be experienced in certain driving conditions. This update improves the low speed engine and transmi
• 5NP-P9A3V-12 Service bulletin
  2016-11-14 · Electrical System — Software
• Eco, Sport, and Limited trim 2016 Hyundai Tucsons are equipped with a 7-speed EcoShift® Dual Clutch Transmission (DCT). In specific operating conditions, the transmission clutch application logic can result in a delayed engagement when accelerating from a stop. If the accelerator pedal is steadily depressed for approximately 1.5 to 2 seconds, the vehicle will begin to accelerate and normal driving
• 5NP-X7Y4J-12 Service bulletin
  2016-11-14 · Electrical System — Software
• This bulletin provides the procedure to update both the ECM (Engine Control Module) and the TCM (Transmission Control Module) on some 2016 and 2017 Hyundai Tucsons equipped with a 7-speed EcoShift® Dual Clutch Transmission (DCT). The update will address: ? A slight hesitation at low speeds that can be experienced in certain driving conditions. This update improves the low speed engine and transmi
• 5NP-V2N3H-09 Service bulletin
  2016-08-17 · Engine
• THIS BULLETIN PROVIDES A PROCEDURE FOR REPLACING THE THERMOSTAT ON CERTAIN 2017 ELANTRA VEHICLES. THE THERMOSTAT MAY FUNCTION IMPROPERLY AND MAY RESULT IN DIAGNOSTIC TROUBLE CODE P0128. NO DRIVABILITY ISSUES ARE ASSOCIATED WITH THIS CONDITION.
• 5NP-A2Y3D-05 Service bulletin
  2018-04-02 · Electrical System — Instrument Cluster/Panel
• This bulletin provides a procedure for replacing the thermostat on certain 2017 Elantra vehicles. The thermostat may not function properly and may result in Diagnostic Trouble Code P0128. Replacement of thermostat is required even without a P0128 code.
• 19-01-008H Service bulletin
  2019-03-11 · Engine And Engine Cooling
• This bulletin provides information related to an ECM (Engine Control Module) software update for DTC P0128 ?Coolant temp Below thermostat regulating Temperature? logic improvement. There are no drivability symptoms associated with DTC P0128.
• Campaign T3S Dea Service bulletin
  2019-03-07 · Engine And Engine Cooling
• This bulletin provides information related to an ECM (Engine Control Module) software update for DTC P0128 ?Coolant temp Below thermostat regulating Temperature? logic improvement. There are no drivability symptoms associated with DTC P0128.

A stored code names the test that failed, never the part that caused it. The record above is what Hyundai and its owners have filed about it; the code’s page across every make has the whole file.