What does this code mean?
The warm-up performance did not meet the monitor's expectation. Check coolant level only when the engine is cool, compare temperature readings from a cold start, and assess the thermostat and cooling-fan operation. Climate, sensor accuracy and vehicle calibration matter. Never open a hot pressurised cooling system.
Sources and interpretation [1]
A code identifies a detected condition, not a part that must automatically be replaced.
Manufacturer wording
Source wording can vary by vehicle and suffix. It is shown as written, not as a universal diagnosis.
P0128Coolant Thermostat (Coolant Temp below Thermostat Regulating Temperature) logic revisionP0128Coolant Thermostat - Coolant Temp Below Thermostat Regulating TemperatureP0128Coolant Thermostat (Coolant Temp below Thermostat Regulating Temperature) logic improvementP0128Cooling System MalfunctionView all · Manufacturer wording →
Manufacturer communications
248Original wording in English
HYUNDAI
Reported code forms P012800
Certain Santa Fe Hybrid (TM HEV), Santa Fe Plug-in Hybrid (TM PHEV), Tucson Hybrid (NX4 HEV), andTucson Plug-in Hybrid (NX4 PHEV) vehicles may experience intake air line freezing and Exhaust GasRecirculation (EGR) valve…
HYUNDAI
Reported code forms P012800
Certain Santa Fe Hybrid (TM HEV), Santa Fe Plug-in Hybrid (TM PHEV), Tucson Hybrid (NX4 HEV), and Tucson Plug-in Hybrid (NX4 PHEV) vehicles may experience intake air line freezing and Exhaust Gas Recirculation (EGR)…
HYUNDAI
Reported code forms P012800
Certain Santa Fe Hybrid (TM HEV), Santa Fe Plug-in Hybrid (TM PHEV), Tucson Hybrid (NX4 HEV), and Tucson Plug-in Hybrid (NX4 PHEV) vehicles may experience intake air line freezing and Exhaust Gas Recirculation (EGR)…
SUBARU
Reported code forms P0128
This bulletin announces the availability of new reprograming files for the Engine Control Module (ECM) developed to remedy the following DTCs: P0016, P0017, P0018, P0019, P0014, P0024, P0128, P2109. If any of the DTCs…
MITSUBISHI
Reported code forms P0128-00
This Service Campaign Bulletin sent to dealers provides instructions to reflash the ECU to address fault codes P0128-00, P2096-00 and P050A.
MITSUBISHI
Reported code forms P0128-00
This Service Campaign Bulletin sent to dealers provides instructions to reflash the ECU to address fault codes P0128-00, P2096-00 and P050A.
Check vehicle applicability
839A listed vehicle is a research lead. Confirm the engine, production range and software in the manufacturer's information.
| Make | Model | Model year |
|---|---|---|
| Acura | CL | 2001 |
| Acura | NSX | 2017 |
| Acura | RSX | 2002 |
| Acura | TL | 2001 |
| Acura | TL | 2000 |
| Buick | ENCLAVE | 2021 |
| Cadillac | CT6 | 2020 |
| Cadillac | CT6 | 2019 |
| Cadillac | CTS | 2003 |
| Cadillac | XT5 | 2021 |
| Cadillac | XT6 | 2021 |
| Chevrolet | BLAZER | 2021 |
Historical records · 4 · Historical vehicle association; OBD-II compatibility is not established by this record.
Before replacing a part
Record codes and freeze-frame data. Check battery condition, related codes and visible wiring or hose damage. Follow the vehicle's diagnostic procedure and test results before replacing parts.
Sources and interpretation
These explanations are editorial summaries of the linked manufacturer material. PDF page numbers count from the first file page. Original publications are in English; translations are reference aids. A cited edition is not a claim that it is the manufacturer's latest instruction.
- 2024–2025 MY OBD System Operation Summary for Gasoline Engines ↗
Ford Motor Company · PDF page(s) 71 ·
Source check date · 2026-10-27
Can I keep driving?
A code alone cannot establish whether driving is safe. A flashing malfunction light, severe shaking, overheating, oil-pressure warning or loss of braking or steering needs prompt attention. Stop in a safe place and seek assistance when control or engine safety is affected. Follow the vehicle handbook.