Maf/ait or coolant sensor

Afternoon guys, I was just wondering if anyone can clarify which sensor is responsible for sending the temperature signal to the ecu to activate the glow plugs on a 2003my td4. This is the engine with combined maf and ait sensor next to the air filter or is it the coolant sensor that sends the signal? I only ask as the glow plugs are working after start up to help with emissions but do not work to pre heat. Any input would be greatly appreciated

RAVE says
The ECT sensor is located in the engine block at the front of the engine. It provides the ECM with engine coolant
temperature information. The ECM uses this ECT information for the following functions:
l Fuelling calculations.
l Temperature gauge.
l To limit engine operation if coolant temperature is too high.
l Cooling fan operation.
l Glow plug operating time.

But I think the MAF air temp has a say in it as well !!

td4 glow plug operation ..
see attached pic :

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which sensor is responsible for sending the temperature signal to the ecu to activate the glow plugs

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coolant temp. sensor
if that sensor doesn't work .. a.i.t. sensor data is substituted ..
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