2008 yaris loses power on the motorway no fault code

[Andyc77]

Hi all, Im really hoping someone can help. My wife has a 2008 yaris d4d 1.4 diesel, we bought it from my parents who have owned it from new, it has a full toyota main dealer service history and is on 85k miles, its a lovely little car and in Toyotas own words “mechanically impeccable “

My wife drives the car and on occasion at motorway speeds the car loses power and will not shift down gears to compensate, even manually. My wife has to wait for a lay by and pull in, losing power all the time. If she turns the engine off and waits a few seconds then restarts, its fine again. There are no warning lights, no fault codes, toyota had a look and couldn’t find anything. It can happen hot or cold engine temperatures, and very sporadically, eg it recently went to cornwall and back (300 mile round trip) no problem But it just happens so sporadically.

ive gently cleaned the MAF, its not air filter etc as its just been serviced at Toyota. Its really quite dangerous and my mrs is losing faith in the car. Ive read a bit about the accelerator sensor but there are no fault codes or anything, it truly is an enigma and id be grateful for some help please 

many thanks

[jthspace]

Fuel flow being interrupted? Fuel filter? Does amount of fuel in the tank affect when this happens?

Many years ago I had an Austin that did similar and it was the fuel filler cap that was at fault, probably not this issue but it triggered "fuel" as a possible cause in my mind.

[Andyc77]

Thanks Jeff, the fuel filter was replaced not so long ago and we dont run the car lower than 1/4 tank. 

The best way my mrs can describe it is that the car gets ‘lost’ in where its gears should be shifting, it wont shift down automatically or manually when it happens and seems to go into a limp mode, but with no emergency lights or codes!

i really don’t want her to get rid of it as its a solid little car and its been well maintained since new!

[Stevie J]

I seem to remember reading somewhere on here that someone had issues with the fuel pressure regulator going faulty on his d4d causing issues, as these cars dont seem to have tank mounted fuel pumps and rely on a system than sucks fuel out from the tank, and use a pressure regulator, if this regulator is going intermittently faulty, it may well lead to the engine becoming fuel starved.   

I assume from what I am reading the car has a semi auto transmission - ie, multimode. These transmissions do tend to be rather unreliable and suffer with a high failure rate - if there is no issue with the fueling system, then it may be a problem with the transmission not shifting properly or the clutch slipping, although in this instance, with the problem being intermittant and not throwing a fault code, proving a transmission fault would be quite difficult as intermittent problems are always the hardest to resolve. In the first instance, it would be best to see if the problem lies with the fuel supply system and regulator.

[Andyc77]

Steve, thank you so much for your reply, yes its the semi automatic gearbox, she cant shift it down when it happens to get a higher rpm, this definitely sounds like its worth investigating. Ill start researching now! Thank you again. 

[Stevie J]

If the car has done 85K and is still on the original transmission, and this has never had a repair before, then really it has done very well. They were not the best transmissions Toyota ever produced and there are many threads on these forums about the multimode and problems owners have had with them. If the problem does turn out to be with the control system for the multimode transmission, as is often the case, a word of warning is they are pretty expensive to repair and not all garages will repair them. You may well have to consider carefully that the car being 16 years old soon, and with 85K on it, it may not be worth the expense of repair unless it is in exceptional condition and only the transmission is at fault. But at this stage, we cannot prove a fault with the transmission and without any fault codes being thrown or warning lights, the cheaper solutions should be sought first such as testing the fuel delivery system before starting down the road of fault finding the transmission, as I said, not many garages will service the multimode and those that will will likely want high prices for their services.

[Andyc77]

Steve, thank you so much for your reply, yes its the semi automatic gearbox, she cant shift it down when it happens to get a higher rpm, this definitely sounds like its worth investigating. Ill start researching now! Thank you again. 

 

Thanks Steve, sorry i cant quote your second and very interesting reply! 

The weird thing is it only does it on the motorway, we regularly drive on local de restricted roads and even though it gets to 5th gear on these roads, its never list power at these speeds.

i saw something about the accelerator position sensor can throw the gearbox out of sync but this is only what ive read. 

Its so frustrating as the car is absolutely immaculate, its been owned since new by my parents who garaged it, i think it had a recall at some point but im not sure what for. 

Very much appreciate your time, thank you