My lovely 2.4 2005 Alphard has failed its MOT on emissions and we would like some help with what else it could be. It's failing on running too rich, fault code is P0171 running too lean. It has been coming up with that fault code for 18mths, we have had the following done; 

* Airflow sensor changed (18 mths ago) 

 

failed MOT last Friday on emmisions, so my mechanic did the following;

* MAF sensor changed

* spark plugs & air filter changed 

* smoke tested for airleak and nothing is leaking

* cleared fault code 

 

Retest today - failed on emmisions...

 

What else can cause it to be running rich - I'm thinking Lamda sensor but believe there is 2 of them, any ideas? Please help. I've 5 working days for a free retest! 

 

TIA - Kate 

 

I was getting P0171 "system too lean (bank 1)" also and cleaning the MAF didn't help - the error would come back.

What fixed it for me was changing the fuel Lambda sensor which, on mine, was a struggle as the previous mechanic had forced the sensor into place and had damaged the thread.

An M18 x 1.5 tap and die cleaned up both the thread on the exhaust and the new sensor which I purchased - I would warn to be on the lookout for ones with the correct plug on the end as the cheap ones come with bare wires that need to be housed in the original socket (as the supplied ones don't stand a chance of fitting) and are bound to cause issues.

I ended up getting this one:

https://www.autojapspares.co.uk/toyota-alphard-anh10-anh15-24-front-fuel-ratio-sensor-34437-p.asp

Which is rather expensive but arrived quickly and was a straight plug in.

 

If you haven't located the fuel lambda sensor look at the exhaust manifold cover behind the radiator.

 

I also changed the fuel filter and the air filter - which may have helped but less so that the sensor I would say.

 

Edited August 8Aug 8 by Gamith
Rotated the picture.

Hello Kate you got 2 sensors one is called a fuel ratio sensor which is top one close to manifold this is the most common one to bring the code up if this failing it will run rich if you pm me your reg no. I will give you part no. And drawing where located and link where you can buy it 

The link gamith gave you is the correct sensor 

You should be able to find the correct sensor with the correct plug. The number for my 2007 was the part number that Picasso gave me. The ones with bare wires are for the sensor after the Cat.The wiring for that is quite long and needs to be connected to the old plug and wiring. I had purchased a new after Cat sensor prior to having the stainless exhaust system, but the wiring was too short and I had to purchase the one with  bare ends and fit myself[the new sensor included wire connectors and connected colour to colour using to original plug.  I hope this makes sense!!

Oh - I also found one of these very useful, together with a standard socket wrench.

https://www.autodoc.co.uk/yato/13648886