Grinding noise

[WazWii]

Hi,

 

I was hoping someone could help me. Two weeks ago I had a terrible grinding noise coming from the engine bay when returning home from a drive-out in my Toyota Aygo. It is an MMT gearbox version. The grinding sounded like two metal parts clashing and grinding on each other. It was loud. Interestingly this first happened when I came to a near standstill when lifting off the accelerator (no brakes were used for this) and as the gearbox was automatically downshifting. I immediately pulled over and then continued for a little while longer (no noise at idle). The noise sadly returned when driving off again and I swiftly returned home. Luckily I was just a street away so was very very lucky otherwise I would have been in deep trouble stranded far away from home. 

 

So was this a gearbox problem? Some issue with the selection of the gear? Or the clutch? As I completely slowed down after hearing the noise I could not tell if there was a loss of power but I think there was. I trickled my way home. Perhaps I did smell a slight whiff of burning but hard to be 100% sure. No warning lights came on the instrument dashboard and I know the Aygo has transmission (failure/excessive heat) warning lights built into the instrument dashboard. 

 

Interestingly I have now had three drives since testing for the issue again and it has disappeared. The initial test was to see if the car would start as my TOYOTA dealership was stating I have to get the car to them myself. Later they agreed to have someone sent out to collect it. However it is worth stating that the car had an MOT at this dealership (which it passed) and the noise only came after the first drive since the MOT. So I was very upset and personally I find it a bit strange that such an issue would appear since the MOT.

 

Sadly (and I should not have told my dealership in hindsight) at the MOT I told them to investigate a slight burning smell from my clutch when the MMT gearbox automatically downshifts on steep hills (thus making the engine rev excessively). This was not a major issue and I lived with it for three plus years. It was only on the off-chance I told them to investigate. Someone did therefore take the car out and test for this issue and they did state they also smelt something and that it needed further investigation.

 

As stated no noise now since the incident and I would rather not send the car in because it will have to be stripped perhaps and who knows what other damage could potentially occur. I am not happy at the way I was treated by the TOYOTA dealership but I will have to manage this myself. I was hoping someone on the forum could potentially shed light on what engineering problem this seems to be.

 

Thank you.

[martswain]

It is not an issue that is likely to be covered by an MOT test, so the dealer is not to blame for anything and seems to be pretty much on the ball.

If you have had a burning smell on and off for more than 3 years and not done anything about it you are walking on thin ice.

The dealer has assessed the issue and advised it needs further investigation, so you either do that with the associated costs or risk a major failure.

I fail how to see any damage could occur in a strip down, they may find other issues but you would need those to be fixed anyway.

 

 

 

[WazWii]

Thanks for the reply.

Can anyone else help out? I am still trying to understand what happened that day. 

The burning smell only happens on rare occasions when for instance going up-hill. The MMT downshifts, revs go high, and once over the hill when you can upshift due to revs and hill angle dropping the burning smell enters the cabin. I assumed it was a design-flaw in the MMT, engine and hill angle that the computer/engine could not foresee, i.e. just the way this car is designed from manufacturer with its small engine. 

Car is under official TOYOTA warranty. No problems up until this point. Dealer has recently advised car can be driven without worry as problem has not come back.

Other day was thinking maybe it was a fault in the transmission itself. When I slowed down obviously the MMT automatically had to downshift and it did. The MMT can be clunky doing this when reducing speed approaching a T-junction and it does make some clunking noises. Maybe something went wrong there with automatic gear selection and all I had to do was to move the shift level to neutral to de-select everything and then noise would have gone away? That is, it was a gearbox timing issue, an error.

Reason I am hesitant to go back to the garage is they may bill me for something that does not need doing or find associated issues. This will then bring many arguments to the fore because said issue only happened on the first drive out since the MOT which is odd. Car is under warranty but after said episode not sure I want to go back to this dealership - I am looking at my options elsewhere.

 

[Chris Boddum]

The burning smell and the fact that there are grinding noises from the engine bay all indicate some kind of transmission or clutch issue to me. I've heard that it's relatively normal for the transmissions to sometimes go into N (neutral) and just not do anything. However, I've not heard of the above. It sounds like the clutch is not doing its job properly causing a burning smell and grinding gears. I can understand your hesitation from taking it in to Mr. T, but this might be something that will be worth the money having looked at.