howardo
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The pre-heat time is controled by the ECM using info from the coolant temp sensor. The ECM changes the pre-heat time depending on the temp of the coolant, which gives indication of the outside temps. The warning light indicates that pre-heating is taking place. Maybe on a td4 pre-heating doesn't always take place, I would wait for more replies from owners of td4s, sorry I have an l-series which is a bit simpler.