Unlike conventional thermostat that is controlled by coolant temperature only. MAP thermostat has an additonal electrical heating element commonly mistaken for engine temperature sensor.

Wiring connection and operation of heating element are monitored by DME, through temperature the sensor located at coolant outlet (app 110 Deg C). Upon installation of new thermostat, reprogram DME. (MAP codes 139/140)

Defective DME, wiring, temperature sensor, and poor coolant circulation due to clogged radiator etc, will result in MAP fault codes 139/140 as well.

In addition to poor engine performance, if the heating element is engaged due to any of the above, engine will operate at temperature too low for proper heater operation.