(Another) Engine Management Warning light

[Rob69]

Hi Stu - Reckon you're on to something with the faulty secondary water pump and it's connection to EGR cooler and dpf regen cooling after engine is stopped.

[Stu Sheridan]

Thanks both, I'll start to make some plans to source and replace - that's if I can't find an obvious feed or plug issue first.

I'll deal with the added risk of cooked turbos, warped heads etc by letting it idle for a few minutes whenever I come to a hot stop.

[Stu Sheridan]

Your latest code is an EGR fault? The MAF faults are months old.

I'd hold off the MAF purchase just yet. The codes should be cleared and then see if any come back.

It could be that the EGR is not functioning correctly due to a faulty N18 valve.

New, you would be looking at £100 to £120 for the Bosch OEM MAF unit. The VW part number for the MAF on your car (CBAB engine) is 03G906461C which will be a Bosch unit. Cheaper versions exist but questionable quality and longevity. I always fit the Bosch.

Second hand working anywhere from £25 upwards.

Easy fit but you might need a large pair of scissor grips as the spring bands are thick and a bit awkward to manoeuvre off.

Not sure the MAF is the problem though.

I'd like a bit more advice about the N18 valve if possible - I've had another "lack of power" moment today - on the same hill unbelievably. I'm cruising happily at 70mph, start to climb a hill on M65 and I've got no power. Manually dropped down to 4th and and maintained 65mph. Allowed the car back into 6th closer to the top and after a few seconds I definitely felt a surge as (what felt like) the turbo came back in/power returned and I was able to back off the throttle. Second time this has happened and on the same hill.

Does it sound like the N18 could be responsible?

The car generally runs fine - I'm in the process of deciding whether to just go ahead and fit a new secondary coolant pump as previously discussed but feel I also need to sort this issue.

Just to recap: EGR cleaned out, MAS tested with VCDS and looks to be bang on the money in terms of predicted vs actual, still getting both codes though, EGR & MAS.

Is there a way of simply testing the N18 or ruling out the MAS? I don't have a mityvac but could get one if necessary.

EDIT: Hang on.... the egr is electronically activated, would it have vacuum hoses and an n18 valve?

[Stu Sheridan]

A bit of a further update for anyone not sick of this yet :)

I've bought VCDS and started to tinker with it a bit to try to understand my fault. Still got the MIL coming on every journey or two, causes are always EGR & MAS fault. Happily the 'Coolant pump 2' code hasn't come back!

I'm not sure I entirely understand what I'm seeing but think I'm starting to get it. Using Meas. Blocks 003 The EGR Actual (was previously MAF Actual on older versions) is almost constantly lower than specified whenever the car is under load. It never got much above 600, even when 950+ was specified. Every now and then it drops right down to about 380 even WOT and requested at +950. At these times the power drops off, hills are a struggle, then all of a sudden it comes back and I'm cruising again.

I've logged a couple of journeys, 30 milers with a mix of town and motorway (to work and back tbh...) and its really clear that the EGR actual is very low all through the periods of low power - I added actual boost & specified boost to the log. When the EGR actual comes back up, boost increases and power come back.

So I still don't know if its a bad MAS, a bad EGR or a turbo issue! would a turbo issue cause the EGR actual (which actually the MAS value, EGR cant measure airflow) to change?

As far as I can tell, its not a rip in a pipe, boost leak or anything similar and the intermittent nature of the fault (or at least time of worst performance) seems more like component failure to me.

EGR duty cycle seems a bit odd, spends most of the journey at 100% (is that open or closed?) and never drops below 40% at any time - does that sound right?

Does the graph give anyone any clues to point me in the right direction?

EGR Graph.jpgEGR Graph 2.jpg

[Stu Sheridan]

Just done 30 miles with the EGR disconnected. Car is smoother, pulls better and mpg has jumped to 47mpg from 42/43mpg.

Think I'll replace it!

Sent from my GT-I9295 using Tapatalk

[Stu Sheridan]

Really getting frustrated with this now - its still not fixed!!!

So far I have:

Had a complete EGR blank and delete
Replaced the MAF with genuine bosch
Checked (most) of the induction loop for vacuum/boost leaks - thought I'd found one when I discovered one of the anti shudder housing bolts loose - tightened but made no difference.

I can feel a difference with the new MAF, its a little better from a standstill and pulls a little better at low revs, less hesitation from the lights etc. As soon as I'm on a fast road though like a motorway or dual carriageway I'm back to the same old fault. No power in 5th/6th at 60/70mph. I can get up there if I drop to 4th and floor it. Very smokey when being booted and when trying to get up to speed, slip roads and the like. Constant "booting" and smokey driving is doing my DPF no good, its regenning almost daily and my MPG is crap.

I think a dodgy EGR can now be completely ruled out as its blanked and not bneing "looked for" by the ECU. The new MAF seems to have made some minor improvements but hasn't cured the worst bit of the fault - I've logged VCDS and there is still a big discrepancy but I am seeing reading above 800 so I think that also rules out a bad MAF.

What else can cause this discrepancy? Really hoping for advice on what else I can check and how to check it!

Still throwing up fault codes too - MIL happened this morning on overrun cycle slowing down for motorway exit (often throws the MIL in that situation). Not checked it yet but I'll bet its another P0101 - MAS Implausible signal or P0402 - MAS over/under reading. Will check it tonight.

MAF Graph.jpg

[DMitch16]

Silly question but have you checked your air filter and incoming pipework to ensure it's clear and the filter in order?

If the MAF is good has the wiring to it been checked?

Also was the EGR blank / delete a DIY job or done at a garage and have you had it mapped out?

[martin1810]

Never have an egr delete done when you are looking for a fault. That just makes things harder to understand.
How do you know the egr delete was done correctly?
To test MAF and egr you must accelerate in 3rd/4th smoothly up to 4000 rmp and log with vcds.
Post results. This cannot be done with egr deleted though.

[Stu Sheridan]

Hi Chaps, a bit of an update.

I had the EGR delete done professionally, its blanked and mapped out. My engine, CBAB, has two EGR systems however, a high pressure system and a low pressure system. It was necessary to map the 2nd system closed after the original delete didn’t cure the fault.

Agree with you Martin about fault finding methodology and if I was in a similar situation again I would probably do things differently. At the time though the procedure seemed a similar price to a new EGR and it has, eventually, worked. By the time I got it done I had checked all vacuum and boost lines for leaks, replaced fuel filter, replaced air filter, replaced the MAF, done multiple logged runs from standstill to redline up motorway hills and run out of other things to look at.

The garage assured me that it sounded like an EGR fault to them too and we should be confident that a delete would solve the problem – it did eventually when we realised that there were two systems to be taken into account.

While it was there I had a stage 1 remap too.

The fault has gone, I now have power in all gears at all speeds/revs. MPG is up both by instrumentation and real world tests.

I’m not 100% happy yet, the car is still a little smokey under hard acceleration and suffers a bit of lag (but it’s a DSG….). it actually seems to be improving the more I drive it though, I think any accumulated crud is being blasted away, the DPF has settled down and the DSG is learning to accommodate the increased power.

I have a feeling it’s possibly a little over-fuelled and I don’t think it’s delivering the kind of bhp (175) that I was told to expect so may ask for the map to be tweaked a little once I’ve driven it further and got more used to it.

[martin1810]

The garage having problems with a simple egr map out is odd. It is not a difficult job.