Reduced Performance mode triggered under hard acceleration

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Another featurette that has started cropping up fairly regularly with my S-Type (diesel) is, when accelerating hard, it sometimes clunks into reduced performance mode....no turbo, nothing.

A couple of things I have noticed when this happens:

  1. It tends to happen if the engine is not fully up to temp and I need to overtake although it has happened later into journeys
  2. If I drop her into neutral and then engage D again, the turbo is back and performance is as before although the trip still shows the reduced performance warning until I turn the engine off/on again.

I used to have an old Skoda that did this and that was because the turbo was over boosting due to sticky variable fins in the turbo.  Not sure if this is the same sort of thing.  The odd thing is why does putting it in neutral then back into drive again return power?  Could it be gearbox/clutch related?  

Only other thing to mention which is probably entirely unrelated.  At times my speedo goes haywire (not at same time as reduced performance though, that I have noticed anyway).  Just sometimes the speedo either doesn't work or is definitely not showing the correct speed.  If I pull to a stop and then pull away again, say at traffic lights, the speedo usually sorts itself out.  I believe the speedo is connected to a sensor on the gearbox and I guess the sensor may be faulty?

Yet another thing for my man at the garage to look at but I have to take it in when the reduced performance has happened otherwise the fault code will be cleared when he gets it.


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only way to know for sure is to plug in and read the codes

could be one of many things, but it sounds like a faulty sensor

seen something as simple as a faulty ABS sensor cause this type of fault

don't think its engine related as usually you have to switch engine off for those to clear



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