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Old 11-15-2012, 08:24 PM
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joyism5 joyism5 is offline
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Location: USA
Join Date: Jan 2011
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Mein Auto: '99 740IL, K75RT
Few things about the thermostat (map one).

The control of the engine cooling system with a conventional thermostat(regular) is determined by the coolant temperature only, while the characteristic of the map thermostat, are that temperature can now be influenced specifically within the thermostat control range.As a result the engine can be operated at a higher coolant temperature in the partial load range, on the other hand, lower coolant temperatures are intentionally set under full load operating conditions. This achieves more eficient combustion thus reducing fuel consumption and pollutant emissions.
The map thermostat is controlled by the engine control module dependent on a characteristic map, determined by the following factors: engine load,engine speed,vehicle speed,intake temperature.
The thermostat still works like conventional one (this one opens at 110Celsius degree ), however, a heating element is additionally integrated in the expansion element . In the event of control intervention by the DME control module, power (12 V) is applied to the heating element integrated in the thermostat. Heating the expansion element means that the thermostat opens at lower coolant temperatures 80- 103Celsius degrees.
The line connection and the function of the characteristic map thermostat are monitored by the diagnosis function in the DME control module. Any faults are stored in the fault code memory of the DME control module. When the coolant gauge is showing the mid-position for coolant temperature means that it reached o 75C - 113 Celsius degrees.

Knowing this , few things that will trigger the map cooling thermostat code could be :
-fault thermostat heating element,
-fault in the coolant temp sensor (the one on the thermostat housing),
-any wiring problems with the above sensor/element,
-a mechanical fault in the thermostat itself.

Any of this could cause the coolant to be out of map , and the code will be stored by the DME.

The thermostat element can be checked with a voltmeter for continuity/OHM, and if receives 12 V at the connector when temp is 73-103C. The thermostat itself can be checked using a infrared thermometer , taking values at the hose after the thermostat.
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