406 HDI 2.0 110HP Engine Light on- 'Limp mode'

[pugface406lx]

Hi anyone help please, my 406 HDI 110 year 2000 'W' Reg has developed a problem.....on the dual carriageway the engine light came on and stayed on. Car went into 'limp home' mode...wouldnt pull above 2600rpm which was frustrating.

Anyway I got a mobile guy to come and read the codes at home....it says 3 things..
1. 0335 Crankshaft position sensor
2. 0101 Air mass sensor
3. 0246 Pressure convertor boost pressure control deviation.

He reset the computer and the light went out and stayed out on the drive as he revved it up....it revved freely right through the rev counter, however when i took it for a run up the main road I got to a good speed and the light came on again and remained on.....and yes again the 'limp home' mode came in and wont let me drive above 2600 rpm.

Anyone experienced this? I dont want to go thro' the computer thing again as its already cost £30.......My hunch is its the Air mass sensor on the air intake near the air filter box but im not too sure. If its the crank sensor would the engine not start?...or maybe cut out?
Not sure what the pressure convertor thing is...maybe turbo?

Help very much needed please

Puggy

[TopDonkey]

My guess would be a split in one of the boost hoses or a split in the intercooler or the small pipe that leads to the boost sensor, if you loose boost, you get an overboost which flags an air mass fault at the same time because you are venting air that was measured in by the air mass sensor but not getting to the engine.

I would be checking my boost pressures under full boost when it isnt in limp home mode, I think you should be seeing about 12psi ?? (only about 50% sure about the boost, someone correct me if i am wrong!)

[pugface406lx]

is it not more likealy to be the air mass sensor at fault...i took it back up the carriageway and was ok as far as turbo kicking in until i reached 2600rpm?

[TopDonkey]

That will cost you money to find out as you would have to buy another one to swap to see if it fixes it !!, i was trying to suggest things that are free to check/fix first, but yes, it could be the air mass sensor at fault

[pugface406lx]

just dawned on me....i have access to another HDI like mine....if i swap the air mass sensor over temporarily...will it clear the fault even though the engine light remains on until i can get it reset?

[TopDonkey]

I think you need 10 succesfull stop starts without the fault before it clears the fault indicator if you dont clear it with a diagnostic machine for air loss related faults (again not 100% sure on that one), because i have an lexia and Peugeot planet its been a long time since i have had to try to get faults to clear themselves

[pugface406lx]

Hi does that mean simply starting and stopping the engine 1o times...or is there more to it?

puggy

[TopDonkey]

I've tried stop starting many years ago without driving it and it didnt clear it, it does seem to need proper little short journeys to clear the fault

[pugface406lx]

Thanks for that top donkey i will try it out tomorrow and let you know..!

puggy

[pugface406lx]

Well I did the swap over of air boxes and air mass flow meter as I said and it worked...straight away the engine pulled through the revs up through the gears ...never went into 'Limp Home' mode and after a few cycles of stopping and starting the car on short journeys the engine light went out.....Hurrah. So all I need do now is get another Air mass sensor from somewhere.....maybe a scrappy or similar.

Thanks again guys....great help as always

Puggy

[Doggy]

Sometimes they only need cleaning...

(No personal experience on 406's, but many consist of a heating element & temp sensor - the greater the airflow the cooler the temp. Some have a circuit board in the air stream & are very fragile, others respond well to a spray with brake cleaner).

[steve_earwig]

I *think* they're just hot wire (although they might not be...), if it's goosed you've got nothing to loose by giving it a squirt.

[pugface406lx]

seemed to have cured the problem guys...its the air pressure sensor located at the front (near bonnet slam panel) on a little bracket mounted to the condensor.....its a Denso item.....has an elec connector and a small air tube which connects to the turbo intercooler pipe.....swapped it out and hey presto...no more 'limp home mode'.....and fuel economy has got better too.

pugface