Unpredictable limp mode

[pat123fish]

Hi,my on going problem!!!
I have a Passat 170 tdi sport 2006.Bought 2008 with 40,000 and 8mths warranty left.
In early 2009 i had a prob with the limp mode coming into play with the usual message and symptoms.
I pulled off the motorway and restarted the car and all was well.
I took it to the main dealers for a read out three days later.
On picking it up they informed me that nothing had been listed as a fault.
A few weeks later while driving on motorway again at steady 80 Cruise control on and it went again.Pulled over and turned off (reset) then on way again.After several times during a couple months driving i went to dealers and told then all was not well.
Car now out of warranty.
They put in a new throttle sensor switch and said thats what they THOUGHT it could be as they could not get the car to go into the limp mode on a test drive.
It happened again weeks later,they then reimbersed me for the sensor they had put in as it had not cured the problem and said it was wiring from the glow plug harness and they changed it and a sensor(not sure which sensor they replaced)All the time it was their opinion on what was wrong and not a fault that they could find.
The next few weeks were fine until it went again,this time I managed to get to them with the flashing light,limp mode and the fault message still showing on the MFD.As if i turned the ignition off it put its self right and it didnt register a faulf on the VCDS.
They refunded me all the costs so far and told me they could not find the fault.
So i went away with the car still with this intermittent fault that does not show up on main dealers vagcom(or what they use).Nor can i get it to do it on command
The car then was fine for 4 months and then on the motorway 75-mph last week it did it again.
Has anyone any ideas what i should look for or suggest anything please.
Apart from this it is 100% and i love it.Just at the back of my mind i always wonder when it will happen again.I know basics with cars and wanted to try and solve it without the price of the dealers.Even though they could not find the fault.
Thank you

[Quatrelle]

I suppose you can't knock the dealer if he's refunding you each time!

However, are they a genuine VW dealer and are they using genuine VagCom?

[Tups1974]

We are in the process of having the turbo changed on my wife’s 2.0 TDI (140) SEAT Altea, we would be travelling down the motorway and then limp home mode would kick in, pull over, turn the car off and restart it and it would carry on as if nothing had happened. Normally this fault happens after about 45 min of motorway travelling.

This has now happened three times in two weeks so it was a trip of to the dealers - no fault found whilst on their computer. However during a road test the fault happened, which has lead them to believe that the car has a turbo vane fault causing the car to switch into limp home mode – hence the new turbo. I have also heard that the turbo pressure value can get coked up causing limp home mode as well, but in our case they feel it is the turbo – good job it’s still under warranty!

[pat123fish]

Quatrelle,Tups1974,
Thank you both for your replies.
Yes it is a genuine VW garage.Alexanders VW Leeds.They are very good(usually)and i cant fault them with the refunds.My only concern was they put the parts on with a hope through experience that these parts were to blame.I appreciate experiance is great but with these modern engines and computer systems ,i am not happy that if a fault is not found then they replace what they think is the problem.I has tacken it to JCT600 in Wakefield once and asked for a check on the system ,they also confirmed that no fault had been recorded but to fetch it back in limp mode if possible and they can hook it up then without me stopping the car.But this has already been done and still nothing registered.
Not too sure its the turbo sticking as it is only once a blue moon that the limp mode comes into play and i drive the car daily at least 50 miles.I often give it some stick to burn the carbon off and have not had Turbo issues,Turbos usually just go rather than be intermittent ,i am wondering if there is a connection somewhere that is slightly loose but cant think on where to start looking,or what would trigger the limp mode off.I drove down to Northampton Monday there and back 260 miles ,not a problem and as i say it can go for months without an hiccup,then when it does, i turn it off and back on and its reset ????????Then drives like nothing happened.It never happens more than once on a journey i.e if it is reset then it is alright for weeks/months.
I am genuinely stuck with ideas on what to do next.

[martin1810]

The B6 can't really go into limp mode and not set a fault code. Any turbo limp problem will set a code. You can have faults that don't set a code but the ecu won't go into limp mode for these.
Sounds like the car is not going into limp mode, just not running properly. Fuel delivery faults can do this as can MAF sensor faults BUT they won't get better when you switch off and on....usually.

[pat123fish]

Thanks Martin
The car will flash the glow plug sign,message of Garage workshop(or similar)comes up on the MFD, it will lose its power and slowly decrease speed.I can get it to cruise along at about 50mph but if i try to accelerate it will not let me.If i press the clutch in and try to rev the engine it will not go over 3,000 revs.
When i have taken it to the garage,at the earliest opportunity they say it has not registered a fault,hence thats why they put the replacement parts on.When i questioned why they had changed the throttle sensor if it was not showing as being at fault they stated the engineer had 30+years in the trade and the item he changed was the usual thing that caused the problems.On going back to them when it happened a few weeks later they said that it could be a wiring loom fault on the glow plug harness,or a sensor,i wish i had asked which sensor they changed,the bill was £136 for both items,if that makes any sense in valueing the sensor and the harness??
As i was driving to work it happened again.The VW garage is on my way to work so i managed to drive it to them in this state.They gave me the courtesy car and kept the engine running on mine and said they would keep it running and do it the next job.When they phoned later on they said it was not showing as a fault,they could not understand why and i decided that i would take it elsewhere.After an argument they refunded the money as the problem had not been fixed and the proof was that the car was in limp mode and the parts they fitted made no difference.They also mentioned that when the ignition is turned off then back on that no fault has been logged??
If it does it again and i am close to home i will take it to a different garage but as everything is running well and i have been told it does not register a fault i feel like it would be wasting money.
In your experience,what would you have a guess at?Or the possible causes?
Thank you
Pat

[pat123fish]

Martin just to add to my last post.It last happened on the motorway and i put the car into neutral (road was empty and i was in full control and under the speed limit)and turned the ignition off then back on as it was moving and it reset itself as well.I drove a further 60 miles with no further problems,no glow plug symbol lit up and no message on the MFD.What the heck is up with the car?? So frustrating.

[martin1810]

The garage should have run a complete engine measuring block scan whilst the engine was in limp mode. This can be done with VCDS and might show up any odd parameter. In theory your problem can't occur because the ecu should log a code when it goes into limp mode. A problem in the ecu can screw this up. Has the car been remapped ? The strange thing is the way it resets. A faulty MAF sensor can cause your problem and not set a code, but it will not usually reset when you switch off.

[pat123fish]

Martin ,i really do appreciate your replies and time spent answering.
It has not been remapped and was a company car with full service History with only 39,000 miles when i bought it.
The History shows it had 2 front suspension arms fitted,a lower turbo boost pipe and two rear parking sensors at a service when 34,000.
Since then and apart from the cam belt and water pump change at 57,000 and oil change every 10,000 it has been 100%.
these repairs and services(apart from oil changes by myself) all done by main VW dealers.
You mention the MAF sensor?Is there a way i can either test this or clean it out,or does it just develop faults.
I have tried my hardest to get the car to fail on my days off work,just so i can take it to the VW garage near me,for a read out (not the one that has done the previous work).However it will not fail on command.This is the confusing part as i know there is a fault but not sure on when it is going to go again and how important it could be if it did not reset itself.
I mentioned that on the motorway when it went into limp mode, that i turned the ignition off and back on in probably 3 seconds,still travelling at 70+ and all was well again for the next few weeks and has not done it since,what ever the weather or my style of driving has been.
What would you be doing next if it was your car?
Thank you again for your time
Pat

[martin1810]

I don't think there is anything you can do unless you buy vcds and a laptop and keep it in the car ready to run a log as soon as the limp mode happens. It is strange because switching off and on should not reset the problem if it hasn't set a code. A faulty MAF sensor can produce your symptoms but it doesn't reset with ignition off/on. Cleaning the MAF is not likely to help. You can't test the MAF unless the car is in limp mode and you have VCDS handy. You may have to ignore it until something gets worse and sets a code.