Engine management light / limp mode

[williamg1988]

Hi there, I've been reading on the forum for years but just making my first post here, thanks for all the advice on many issues, and thanks in advance for anyone who may be able to shed some light on my current predicament!  

For a while my van has been going into limp mode (the revs are limited to 3000rpm) it usually will happen after driving for about half an hour and then when accelerating up a hill it will loose power and go into limp mode along with the EML coming on.  If I switch the engine off and back on it comes out of limp mode but the EML stays on.   Occasionally the EML will be go off again, but then soon enough its back on along with the limp mode. 

I finally got round to buying a code reader - there were I think 7 codes present, which I cleared.

I then drove a few miles and checked the codes again before the EML came on, the codes present were - 

P0409 - EGR sensor A circuit
P0401 - EGR Flow Insufficient
P1162 - manufacturer control
P0490 - EGR control circuit A high
P1351 - Manufacturer control

Amazingly it has then stayed like this for almost a month without the EML coming on.  Then yesterday the EML came on again along with the limp mode.  I stopped and checked the codes which were as above but with the additional ones below

P0234 - Turbochager / supercharger overboost condition

P0100 - Mass or volume air flow circuit


So I would guess that this means its the P0234 or the P0100 that is causing the limp mode?  Does anyone have any experience of this and where I should start looking in order to fix the issue?  

And with regards to the EGR codes, how serious do people think these could be, there seems to be conflicting advice on EGR blanking... If the EGR related codes arn't making the EML come on are they really much of a problem and can I just ignore these ones....?

My van is a 2007 1.6hdi

Many thanks if anyone can share any advice on this.

[Sol]

The M59 can have the EGR blanked, with no fault light coming on but that would cause a fault code to be stored for incorrect airflow, which you would only notice in a scan. Hard to say, could be a boost error in reality as the EGR wouldn't cause limp mode but boost errors will. Problem with a code scanner, is you can't read live data like actual boost Vs requested etc.

You could do that with a Bluetooth OBD adaptor and an app on the phone, like Torque Pro or FAP pro. Not as good as DiagBox but lets you see boost as you drive.

I'd suspect the MAF too, what to try is unplug it when the ignition is off, then start the van and drive it for a while. You'll get an EML but it might pull fine on the default map for airflow and that could point to a bad MAF. This can cause errors and limp mode from a bad reading, sticking as the revs rise.

[jj9]

If you've been reading the forum for years you can probably guess what my fist step with this problem would be..... and if you can't I bet Zion can. 


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[Sol]

Oh yes, and correct too I bet JJ, fit an EGR blank plate first and see how it behaves after that.

If it all goes away, happy days. At least then the EGR is out of the loop.

The intake and EGR et al, will be coked up with sticky soot deposits so it's a wonder diesel engines work at all with a good few miles on them.

[jj9]

Oh yes, and correct too I bet JJ, fit an EGR blank plate first and see how it behaves after that.

If it all goes away, happy days. At least then the EGR is out of the loop.

The intake and EGR et al, will be coked up with sticky soot deposits so it's a wonder diesel  engines work at all with a good few miles on them.

Give that man a Cigar . . .     


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[williamg1988]

Many thanks for your replies. I don't have a full understanding of how the EGR works... is it the case that the EGR is putting dirty air into the MAF sensor and the turbo? So although its the P0234 and P0100 codes that are triggering the limp mode it may be that the EGR is the root cause of the MAF or the Turbo getting bunged up?

So there seems to be three areas I need to look at -

1) Blank the EGR - I see you are a fan of this JJ thanks for the advice! I ordered a blanking plate a while back but never fitted it as I started getting confused wether it was a good idea or not... well I'll give it a bash then and see if this helps.


2) Vacuum Actuator - Since posting this morning I went and checked the Turbo wastegate actuator, it seems to be springing back fine and the vacuum is working. I am still to follow the vacuum line back to the Vacuum actuator at the back of the engine and also check out the vacuum actuator itself (I read another post suggesting to check the pipe from the vacuum actuator leading to the top of the engine, which can often get blocked)


3) MAF - I'll try unplugging as you suggest.

I guess I do one thing at a time and drive it for a bit to see what happens so I can eliminate each thing..

Does it sound like I'm going down the right route here and is there anything obvious that I'm not getting? Sorry If I'm not quite getting it, I'm pretty new to this level of engine stuff....

[Sol]

Yes, one at a time. Blank the EGR first, then see how it runs. Manky sticky soot from the EGR, clogs it and the intake but it bypasses the turbo and MAF, they don't get the sooty sticky mess BUT it does clog the inlet manifold, reducing 40mm inlet ports (for example) to the thickness of a pencil. Not good, so blanking it is the way to go. No EML but you will always find a "phantom" code for airflow higher than expected but ignore that. It's because more of the airflow is measured through the MAF after the EGR is blanked, and if it still runs shitty, the MAF is probably bad. Especially if it won't rev above a limit and then cuts in with a limp mode error as the throttle is telling it to add fuel but the airflow stops increasing part way up.

[jj9]

All good points.

The problem with fault codes is that they aren't always precise and a lot of the time they can be a red herring.

There's been a few occasions on the forum when members have had problems similar to yours and it's turned out to be the EGR valve even though the valve had been recently cleaned etc.
Fitting a blank isn't a guaranteed fix but at least you will have ruled out a sticking EGR valve and then you can take it from there.

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[Sol]

Just to make clear the rules on EGR blanking, I'll post the official legal guidance on the subject below. All discussions regarding this topic in any thread or in any section of this forum, are based on the personal opinions of the individuals discussing the subject, and are in no way endorsed or encouraged by http://www.berlingoforum.com.

[Sol]

From an article printed in Car Mechanics Magazine:

Car Mechanics asked the DVSA for their response to fitting an EGR blanking valve and they said : "DVSA's priority is to help you keep your vehicle safe to drive, ensuring that it meets required roadworthiness and environmental standards. Vehicles may fail the MoT where emissions control equipment has been tampered with but irrespective of the MoT such modification is an offence*. DVSA continues to work with DfT to persue such offences, including taking disciplinary action against any MoT garages found to be conducting modifications."

* Road vehicles (construction and use) regulations (Regulation 61a(3)). Removal of an EGR valve, diesel particulate filter etc. will almost invariably contravene these requirements, making the vehicle illegal for road use. The potential penalties for failing to comply with Regulation 61a are fines of up to £1000 for a car or £2500 for a light goods vehicle.