Reference meaning
What does this code mean?
The wording below belongs to the named make and communication. Match the complete code, reporting module, model year and engine before applying it.
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.
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.
Scan worksheet →Manufacturer wording
Source wording can vary by vehicle and suffix. It is shown as written, not as a universal diagnosis.
P2CEF00Electrical fault or open circuit in coolant thermostat
Manufacturer communications
3Original wording in English
LOTUS
Emira 4-Cylinder vehicles only - Issue 3 includes updated information on thermostat the testing method and replaces version 2 of this bulletin published on 05.08.2026. Diagnosing medium temperature engine coolant thermostat operation to prevent unnecessary thermostat replacement. The information in this bulletin is intended as a…
LOTUS
Diagnosing medium temperature engine coolant thermostat operation to prevent unnecessary thermostat replacement. The information in this bulletin is intended as a procedure that should be performed if a 4-cylinder Emira has generated Diagnostic Trouble Code (DTC) P2CEF00 Auxiliary Thermostat “A” Stuck Open (see image for thermos…
MERCEDES-BENZ
Complaint Customer states that the CEL is lit in the instrument cluster. Various codes may be active/stored: Stored in N3/10 in model series 206, 254 or 232: P012800 - The coolant temperature is below the coolant thermostat specified temperature. and/or P01169D - Malfunction in coolant temperature sensor 1. Under temperature in …
Check vehicle applicability
16A listed vehicle is a research lead. Confirm the engine, production range and software in the manufacturer's information.
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.