HomeP0128 · Coolant temperature below thermostat regulating temperature
Powertrain

P0128

Coolant temperature below thermostat regulating temperature

P0128
Reference meaning

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.

A code identifies a detected condition, not a part that must automatically be replaced.

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A listed vehicle is a research lead. Confirm the engine, production range and software in the manufacturer's information.

Manufacturer communications

4

Original wording in English

MERCEDES-BENZ, MERCEDES-MAYBACH

Reported code forms P012800

Complaint Check Engine Light ON with DTC P012800 "The Coolant Temperature is Below the Specified Temperature" active and/or stored in the ME (N3/10). There are no drivability concerns related to this complaint. Cause…

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MERCEDES-BENZ, MERCEDES-MAYBACH

Reported code forms P012800

Complaint CEL ON with DTC P012800 "The Coolant Temperature is Below the Specified Temperature" active and stored in the ME (N3/10). There are no drivability concerns related to the complaint. Cause Root cause varies…

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MERCEDES-BENZ, MERCEDES-MAYBACH

Reported code forms P012800

Complaint CEL on with Code P012800 "The Coolant Temperature is Below the Specified Temperature" Cause Under investigation. This is not an issue that affects drivability or performance and is not a safety concern. The…

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MERCEDES-BENZ

Reported code forms P012800

Complaint CEL on with Code P012800 "The Coolant Temperature is Below the Specified Temperature" Cause Under investigation. This is not an issue that affects drivability or performance and is not a safety concern. The…

Read communication ↗

Check vehicle applicability

4

A listed vehicle is a research lead. Confirm the engine, production range and software in the manufacturer's information.

MakeModelModel year
Mercedes-BenzAMG C63S2018
Mercedes-BenzAMG C63S2017
Mercedes-BenzAMG C63S2016
Mercedes-BenzAMG C63S2015

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.

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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.

  1. 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.