Running fan after switching off the engine 2.0 TDI CR DPF

How long after engine shutdown should the fan run? And why is this happening? The noise is quite high. It often happens in BMW, Ford, Volkswagen, Audi or Skoda cars and is normal.

The 2.0 TDI CR DPF (103 kW) engines of Skoda, Volkswagen and Audi often have a problem with running fans. The reason for this is that the engine is switched off during DPF regeneration. The regeneration starts again the next time you drive, but it is better to keep driving the car so that the regeneration doesn't switch off during the drive - it doesn't do the car's engine much good.

You can tell when the DPF is regenerating by the increased idle speed (1000 rpm or more) + a slightly different engine sound. There is no special light in the car for this.

If this problem recurs systematically the solution may be to replace the exhaust sensor (lambda sensor). This is because the fans do not know what the temperature is at the exhaust and so prefer to cool and this causes extreme fan speed. Sometimes the orange check engine light can also come on - this is related to the DPF regeneration not going as it should.

  • The price for a lambda sensor replacement is around $130 / £103 plus the cost of approximately 30 minutes labour.

Believe me, it is not normal for the car's fans to run full blast when the engine is cold. This is precisely because the lambda sensor has failed to warm up to the required temperature to allow regeneration to take place - at the same time, it is sending a signal that it is hot and therefore those fans will come on.

Another common cause is a problem in the EGR, but you

  1. should always start with a diagnostic,
  2. then possibly a lambda probe,
  3. and finally an EGR replacement.

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