How I fixed my P0171 system too lean and car has no power X Reg

Hi All,

Just thought I'd share my personal experience with the above problem.

My wife was driving to work and about half way (15 miles) the engine light came on. She phoned me and asked what she should do, luckily she was near her mother's house at that point, so she went there and got the local garage to take a look. Their advise was 'system too lean , could be an air leak' will have to have the car in to check.

We had an MOT due soon so I decided to let our local garage take a look when that was done. Similar story, system too lean, stuff was check engine light was switched off and seemed fine for about a couple of weeks but then the engine lost power and the engine light came back on.

Not having much money, we couldn't afford to get it fixed at the garage, luckily I work at a College that teaches Motor Vehicle Maintenance, conclusion this time was that the lambda (o2 sensor) had packed up, seemed logical as the graph was all over the place on the ODB2 machine, and would have to bring the car back for more tests.

At this point I thought I'd take over and have a go myself. So i bought a 2nd hand lambda sensor off ebay for 25quid delivered, fitted that, no change. So, after a little more research found this site and the posts about problems with air flow sensors and the later K11s. Not wanting to shell out for a new throttle body, I thought i'd just check the air flow sensor myself. After disconnecting the sensor, the engine was full of life again. :grinning: So, that HAD to be the cause. To fix the problem I would have to get hold of the special 5 point with protrusion 'Torx TX' (Wikipedia) to remove the sensor, got a set on ebay again for 12 quid delivered (more than I needed, think it was the T25 size I used in the end, but tools are always useful), Removed the sensor and found it was dirty, so a can of Wynn's Fueld injection and carb cleaner was bought from Halfords, cleaned all around the wires and inside the sensor holes, refitted, reset the engine light with the battery disconnect method, and all is now fine. :laugh:

Car has more power than it has ever had in the last 3 years of ownership. Seeing as this appears to be a common, and difficult to diagnose fault with the post 2000 K11s, I think a lot of people will have spent more time and money than they should have needed to trying to diagnose and repair their cars. The thing I think that make it difficult is as the sensor is just dirty, and not actually broken, the ODB will still see it as working and not actually show the fault, only the lean mixture one.

I hope this post can help a few people out.(Y)

Wow - identical to the problems I've been having with my X reg Micra.

See my post here:

Long story short. P0171, no power, really struggles on motorway.
Cleaned sensor down air intake (with it still in place) with the carb cleaner. Was better for a while but not for long.
Gradually got worse to the point where I could barely set off.
Unplugged the sensor and it ran great.
Got the Torx TS bits and a £26 sensor off eBay.

eBay sensor runs great over 50mph, but below the power is so uneven. Accelerating is lumpy and not smooth at all. Also think it is eating fuel.

Just this morning I've cleaned the old sensor with the carb cleaner and going to see if that makes a difference. If it doesn't - I'm not paying £100's for a new throttle body and will probably just get a new car...

Thanks for sharing :grinning:
Daym.. If you were to have come into our Autofactors that would have been a first point of call...
Were a distrobuter of Wynns and atleast one of the staff has used the product we recomend! The company has been going since 1975 so the boss has the most experience!