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Electronically Controlled (MAP) Thermostat - How it Works - Fault Codes & Testing Tips

This article describes how a MAP Thermostat Works, Fails & Test Tips

BMW models utilize an electronically controlled engine thermostat. This allows the DME to better control engine operating temperature to maintain efficiency and tailpipe emission standards.


The design of the characteristic map thermostat is similar to that of a traditional wax thermostat. In a traditional wax thermostat, the wax is heated by engine coolant, at a specific temperature the thermostat opens, allowing coolant to circulate and maintain engine temperature. The main difference with a characteristic MAP thermostat, is the DME now has influence on the opening of the thermostat. Using an electronic heater to heat the wax element, opening the thermostat as needed.

Look at the housing of the themrostat to identify it. If it lacks electrical wiring, connector or a harness, it is likely a traditional wax style thermostat.

Traditional Wax Thermostat with No Electronics

If there is wiring to the housing, it may be a MAP-controlled electronic thermostat. Confirm the wiring is not going to temperature sensors using wire color. If no temperature sensors are installed in the housing, it is likely a MAP-controlled electronic thermostat.

MAP-controlled electronic thermostat - Note the Wires at Top of Housing

When Removed, a MAP-controlled electronic thermostat looks similar to a traditional wax thermostat.

The vehicle you are working on can exhibit a fault code for MAP cooling, usually a faulty thermostat. Always inspect the wiring and connector for damage or misrouting before comdemning the thermostat.

Some of the possible fault codes are:

  • 139 Map Cooling
  • P1622 MAP Cooling
  • DMW - 2EF5 DME: Map thermostat, activation - Open circuit error code
  • 7B DME activation MAP cooling
  • 279C thermostat, map cooling activation
  • P1619 BMW - Map Cooling Thermostat Control Circuit Signal Low
When testing the circuit from the DME to the thermostat. Check for switched battery volts and ground to the thermostat. If one is missing, trace the open circuit back to the DME.