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 communications
13Original wording in English
RAM
Reported code forms P0128
Flash: Powertrain Control Module (PCM) Updates Customers must experience a Malfunction Indicator Lamp (MIL) illumination and the vehicle must exhibit/set one or more of the following Diagnostic Trouble Codes (DTCs): ●…
RAM
Reported code forms P0128
Flash: Powertrain Control Module (PCM) Updates *Customers must experience a Malfunction Indicator Lamp (MIL) illumination and the vehicle must exhibit/set one or more of the following Diagnostic Trouble Codes (DTCs): ●…
RAM
Reported code forms P0128
Flash: Powertrain Control Module (PCM) Updates RAM 1500 PickupThis bulletin applies to vehicles within the following markets/countries: North America, APAC, EMEA and LATAM. This bulletin applies to vehicles equipped…
CHRYSLER, DODGE, JEEP, RAM
Reported code forms P0128
Customer complains of a MIL-on condition. Upon further inspection, there is a Diagnostic Trouble Code (DTC) P0128 Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature) set in the PCM.
RAM
Reported code forms P0128
Flash: Powertrain Control Module (PCM) Updates This bulletin involves reprogramming the PCM with the latest available software. Customers may experience a Malfunction Indicator Lamp (MIL) illumination. Upon further…
RAM
Reported code forms P0128
Flash: Powertrain Control Module (PCM) Updates This bulletin involves reprogramming the PCM with the latest available software. Customers may experience a Malfunction Indicator Lamp (MIL) illumination. Upon further…
Check vehicle applicability
4A listed vehicle is a research lead. Confirm the engine, production range and software in the manufacturer's information.
Historical vehicle association; OBD-II compatibility is not established by this record.
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.