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Why are my engine fans running even when cold ?

Why are my engine fans running even when cold ?

This is commonly asked, we see it all the time.

Answer, if you have a diesel engined car or van built from roughly 2007 onwards (in Europe anyway), it will most likely have a DPF filter fitted (diesel particulate filter).

These are in addition to the cataylst and the idea is that they collect soot in the exhaust and store it up.

The DPF has (normally) 3 sensors in the exhaust and a 'pressure difference sensor' keeps an eye on the pressure before and after the DPF filter.

If the pressure drop reaches too higher a level, it will start a 'regen' process.

In extreme conditions it can also put the DPF or emmissions light on the dashboard but the idea is though that this doesn't happen and the DPF filter does a 'DPF regen' to burn off the collected soot.

To do this, the engine management system makes some changes that cause the DPF to get hot, very very hot actually. This then burns off the soot thus making the DPF clearer again and ready to start collecting more exhaust fumes to clean out.

Once these levels have been reached, your car / van will try on every journey to do a regen' right from the off and it runs the cooling fans to keep the engine temperatures under control while it does so.

These systems are not totally reliable and the sensors go wrong all the time, so if you need anything to fix yours, please use our contact us page (not all our stock is online all the time and it's VERY hard to work out which sensor you need without expert advice)



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