Peugeot 406 HDI (year 2000) - EGR Code P0401 - MAF Sensor problem

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Fri 17 Dec 2010 12:14
Peugeot 406 HDI (year 2000) - EGR Code P0401 - MAF Sensor problem - su37

Hi all - am new user and greatly appreciate any help at all!!

My pug recently developed P0401 "EGR insufficient flow" so I removed and cleaned EGR pipe and surrounding pipes out although they were not all that clogged. This is accompanied with severe lack of power (limp mode i guess). Next I tested EGR valve vacuum operation - again seemed fine and also did basic check of elec current - seems OK. Also checked servo operation, for hose leaks down to turbo - again no probs detected.

Had fault cleared, ran car, no difference ie; no power and fault code returned. Next cleaned MAF (Airflow) sensor on engine intake pipe but also no difference.

$$$ Ran the car with MAF sensor unplugged and power fully restored again - hooray!! (not a permanent fix though).

Does this necessarily point to faulty MAF sensor though (£90 - ouch)? - you see my mate who works in Peugeot parts says they very rarely sell these. So before I buy this any ideas??? - i mean the fault is P0401 EGR...

LAST NOTE:- just prior to all this, battery totally died, so replaced it - P0401 came on very shortly after this - although I can't see a connection unless when new battery was connected it put a spike through the ECU causing reoccuring spurious code - again any ideas welcome....?

many thanks ---> SU37

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Fri 17 Dec 2010 12:30
Peugeot 406 HDI (year 2000) - EGR Code P0401 - MAF Sensor problem - Collos25

Your mate is probably correct as most people buy them from other sources much cheaper,if as you say it runs better without the Maf I think that is the problem part.

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Fri 17 Dec 2010 12:57
Peugeot 406 HDI (year 2000) - EGR Code P0401 - MAF Sensor problem - injection doc
the only way to be sure is to have a diagnostic tool plugged in and read the live data from the air flow meter to see if it responds, when you unplug the meter it goes to a defuault setting which will increase the fuelling which may in turn be masking another issue.
I would check live data first to be sure otherwise its expensive guess work!

I have experinced these loosing total power & restored it by adding fuel line cleaner neat into the fuel filter when hot, then run for 40 seconds then leave overnight Then re-start in the morning with couple of bottles in the tank & this has restored them to full power.
I have normally used Comma Injector magic 2000 diesel.
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Fri 28 Jan 2011 16:27
Peugeot 406 HDI (year 2000) - EGR Code P0401 - MAF Sensor problem - su37

Thanks guys,

Did get round to using the Diesel Magic but no noticable difference, However have since removed MAF sensor and cleaned all surfaces with solvent - reinstalled and whaddayaknow, power totally restored...!! Hooray.. (i saw a similar posting where somebody had same remedy).

Still have to sort EGR Code P0401 - so if anyone has any further suggestions they are very welcome...??

Meantime all input you kindly provided thus far is really appreciated....

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Tue 22 Feb 2011 16:21
Peugeot 406 HDI (year 2000) - EGR Code P0401 - MAF Sensor problem - su37

Had codes erased recently and touchwood no return... Seems to point that EGR Code 0401 had some sort of link with the MAF sensor problem - can't imagine why though but that's engine management for you.

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Tue 22 Feb 2011 20:29
Peugeot 406 HDI (year 2000) - EGR Code P0401 - MAF Sensor problem - dieselnut

When the EGR valve opens under instruction from the ECU the MAF should see a corresponding reduction in airflow, as exhaust gas has now replaced the air.

When it didn't see this ( due to the dirty MAF ) it threw up a EGR code thinking the EGR hadn't opened & was faulty.

Just goes to show how these fault codes are just a starting point to an investigation & may not be relied on 100%.

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