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Rattling/Knocking from Front Nearside Power Unit


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For some months now i have experienced a vibration, like a misfire, from the engine accompanied by a knocking/banging noise on light accelerator pressure around the 15-30 MPH. When the accelerator is pressed harder the noise and vibration disappears and the car accelerates well. The garage cannot trace the fault and the spark plugs and petrol treatment fluid addition has just cost £259 from a Toyota main dealer. The car is an Auris Hybrid and done 110,000 miles. it started around the 95,000 mark.

Has anyone other owner experienced problems such as these and if so what was the outcome? The car is used for my driving school business and although none of my pupils have questioned the noise/poor running I'm hoping the car can be sorted before the unit expires leaving me a hefty bill and loss of business.

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I haven't experienced this on our car.  But your symptoms seem to loosely fit this thread (there are lots of threads on that site discussing this - worth a search). I'm sure you know the Gen3 Prius engine is the same as the hybrid Auris.


The title is a little misleading, this seems to happen before 150,000 miles for some owners.

In short, they are recommending cleaning the EGR cooler (time consuming but not too difficult), EGR valve and all the small EGR passages in the inlet manifold. Especially if your car is burning some oil.  No parts needed unless something gets damaged.

Here is another thread with some guide as to difficulty, as more people do this, more legitimate shortcuts come to light and get put in these threads, so it ends up as less of a chore. e.g. The cooling system can be clamped, rather than drained completely.

Access (the major problem for this repair) is harder on a Prius, I think, so if this was your problem then it should be a bit easier and quicker than shown in these guides.


This procedure sounds like a 'when', not an 'if', on any Auris hybrid or Prius Gen3.

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Hi Greg, thank you for coming back to my plight.

I tried searching but the search function seems too basic and I gave up searching after a time.

I've seen the threads you pointed to with regards to the cleaning of the EGR but not the reason which caused the suggestion why the EGR would clog in the first place or what the symptoms were apart from poor running which as I said in my OP clears when I accelerate. It doesn't always occur either which is a pain but I can instigate it for the mechanic but he doesn't seem to be able to do it himself.

Also, it seems a definite downside to the hybrid if this EGR needs cleaning every 100,000 - 120,000 miles. One of our USA contributors reckons on a cost of $1,200 which probably equates to £1,000+ plus here.

Finally, if this EGR unit is such a problem why is it not common knowledge at least amongst the Toyota garage mechanics?

Anyway, thanks for the information.


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Hi Peter,

Diagnosing a noise remotely can be difficult.  I'm making a few assumptions here and I'm happy to be corrected; I'm not a mechanic btw, it's just a vague interest!

My thought was that the engine has suffered a build up of carbon inside the EGR circuit (and also the engine as well) that is beyond normal for a hybrid of your mileage, and that it might be down due to your usage.  Slow driving with frequent turn off (e.g. for verbal instruction?), will not get the engine fully hot. Engine deposits will more readily form in that situation, I would think your routine is badly suited to preventing this e.g. not much fast or motorway driving or heavy acceleration (understandably).

The noises might be due to engine pre-ignition or detonation.  If the car detects these (it has a dedicated sensor) it will rapidly adjust the ignition timing to stop this from happening to protect itself, the engine output will drop a little while this happens, maybe aggravating or even causing the poor running.

I would suggest using a Tesco Momentum or Shell V-Power type fuel to see if the problem is helped, this should happen as soon as it gets through to the engine.  It is the higher octane rating of these fuels that is desirable here, rather than any detergent additives. If it makes no difference then the problem lies somewhere else.

I'm assuming you haven't tried this already, and that your driving patterns are as described.  Does it use any oil btw?  Has the car always been used for driving instruction?

The EGR cleaning is straightforward, the engine is worked on from above.  The hardest/longest part is getting the crud out the cooler, this is best left to soak (Mechanic's time cost alert!) for some hours.  In an ideal situation, overnight.  Goodness knows what your dealer might charge for something left cleaning overnight.  No special Toyota or hybrid knowledge is needed for all this repair, finding out where the taxi drivers go for repairs could save you loads here.  Dishwasher powder and a wine bottle cork are what works best for cleaning the cooler. 

As a DIY proposition (i.e. no labour cost), just to give you an idea, I would look at the expense as being:  some anti freeze, any exhaust type gaskets that get damaged (maybe none), some dishwasher powder, 2 x spray cans of brake or carburettor cleaner, a suitable bottle brush, plenty of rags.

In the next generation of this engine (Prius 4, C-HR, soon-to-be-released Auris) this EGR circuit is completely redesigned for better 'efficiency' say Toyota. The EGR is now fed from after the catalyst so all the gunky hydrocarbons will have been burnt off before they can foul things up in the EGR circuit.  Problem solved.

Hopefully it won't be any of this, and it turns out to be something simpler and more interesting.

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