Car revs running slightly high with fan when engine hot or cold

[JAK68]

Hi, I have a problem with my car where the revs are staying a little bit high but the fan runs even when the engine is cold. The only way of clearing this problem is by going onto the motorway to give it a run, this will clear the problem then it the problem might return a couple of days, a week or even a month later, it is never the same. Does  anyone have any idea what could be causing this?

Thanks

[Ootohere]

Is it a diesel and is it doing regens?

[JAK68]

Sorry yes, it is a diesel, not sure if it is doing regens. How would I know if it is doing regens and how often should it do it?

 

The car runs fine all of the time and doesn't overheat or anything.

[Ootohere]

Someone will be along and explain or look through threads posts on here.

Your 9 year old TDI with a DPF has to clear soot so do regens. 

[J.R.]

1 hour ago, JAK68 said:

How would I know if it is doing regens

 

The following description as as definitive as you could get 🤣

 

4 hours ago, JAK68 said:

the revs are staying a little bit high but the fan runs even when the engine is cold. The only way of clearing this problem is by going onto the motorway to give it a run,

 

At the risk of sounding like the dear departed "Battery Man" you will find the above mentioned in the owners handbook including the recommendation to take it for a run at high revs.

[J.R.]

You dont need to do the motorway run, the DPF will sucessfully regen on the next journey meeting the requirements, after several failed attempts you will get a DPF warning light and maybe a MAxidot message telling you to go for the drive, do not ignore this.

 

I am guessing that most of your journeys are short urban ones say less than 15 miles?

Edited 18 September, 2023 by J.R.

[JAK68]

26 minutes ago, J.R. said:

You dont need to do the motorway run, the DPF will sucessfully regen on the next journey meeting the requirements, after several failed attempts you will get a DPF warning light and maybe a MAxidot message telling you to go for the drive, do not ignore this.

 

I am guessing that most of your journeys are short urban ones say less than 15 miles?

no most of my runs are motorway runs of 30 miles each way (on a weekday), could it be that the DPF needs to be cleaned, would it be worth putting some DPF cleaner in the tank?

[chimaera]

How often is this happening? Normally regen occurs every 200-400 km, depending on driving conditions. More often than that might indicate a problem.

 

If the regen starts and finishes during a motorway run, you'll probably never notice it happened either.

Edited 18 September, 2023 by chimaera

[JAK68]

3 hours ago, chimaera said:

How often is this happening? Normally regen occurs every 200-400 km, depending on driving conditions. More often than that might indicate a problem.

 

If the regen starts and finishes during a motorway run, you'll probably never notice it happened either.

It is random, sometimes it could be weeks and sometimes it could be a couple of days  with me doing 60miles a day (most of it motorway miles). The motorway journey is the only thing that will clear the problem as when city driving it just stays as a problem and the motorway drive will always sort it out

[Ootohere]

You know now what it is all about.

So how many miles has the car done? 

[chimaera]

25 minutes ago, JAK68 said:

It is random, sometimes it could be weeks and sometimes it could be a couple of days  with me doing 60miles a day (most of it motorway miles). The motorway journey is the only thing that will clear the problem as when city driving it just stays as a problem and the motorway drive will always sort it out

Like I said, you could be getting a lot of unnoticed regens while you're on the motorway. A regen only takes 10-15 minutes and could easily pass unnoticed while you're cruising on the motorway. More than likely it is regenerating at regular intervals, you're just not noticing it most of the time for the reasons I've just stated.

 

The telltales are really only noticeable at idle or if you shut down during or just after a regen. You don't need to be on the motorway for a regen to happen either, it'll happily regen while you're pottering around town too.

 

It sounds like your car is functioning normally based on what you've said, there's no need to do anything to it or put anything in it other than fuel.

[JAK68]

48 minutes ago, toot said:

You know now what it is all about.

So how many miles has the car done? 

around 130,000 miles

21 minutes ago, chimaera said:

Like I said, you could be getting a lot of unnoticed regens while you're on the motorway. A regen only takes 10-15 minutes and could easily pass unnoticed while you're cruising on the motorway. More than likely it is regenerating at regular intervals, you're just not noticing it most of the time for the reasons I've just stated.

 

The telltales are really only noticeable at idle or if you shut down during or just after a regen. You don't need to be on the motorway for a regen to happen either, it'll happily regen while you're pottering around town too.

 

It sounds like your car is functioning normally based on what you've said, there's no need to do anything to it or put anything in it other than fuel.

Is it normal for the fan to come on during a regen even when the engine is cold?

 

[Breezy_Pete]

I'd be surprised if it was possible for an active regen to be initiated with a cold engine.

[chimaera]

54 minutes ago, Breezy_Pete said:

I'd be surprised if it was possible for an active regen to be initiated with a cold engine.

It actually does. I can't say I'm a fan of it, but there you go.

[Breezy_Pete]

How odd. Thanks.

[TasMan]

Definitely sounds like the normal regen process.

You can actively monitor your regens and DPF health via your phone (if keen!).

Get a Carista or similar OBD reader and plug it in to the car.  Download the VAG DPF app and connect it up via bluetooth to your reader.

I found this link quite informative...  https://www.hypermiler.co.uk/dpf-diesel-particulate-filter/vag-dpf-review-andriod-vag-dpf-monitor-app

I try and allow my car to fully complete the regen process each time, not sure it makes a difference but I'm an engineer with OCD and it just seems like the right thing to do lol...

 

Cheers
Dave

 

[J.R.]

4 hours ago, Breezy_Pete said:

I'd be surprised if it was possible for an active regen to be initiated with a cold engine.

 

Mine became bad when Imoved to my present location because the journeys were long enough to start a regen but not long enough to complete it, when one was interrupted it would restart again the next day within a couple of miles, well before the oil temperature was at the threshold.

 

I either did an unecessary  journey extension to allow it to complete or put up with it constantly retrying, my fuel consumption went way up but thankfully the oil was not yet getting diluted.

 

I had had enough so I paid for the emissions fix to be rolled back, in the 18 months and probably 25K miles since I have only heard the fans running twice at journeys end.

[J.R.]

5 hours ago, JAK68 said:

It is random, sometimes it could be weeks and sometimes it could be a couple of days  with me doing 60miles a day (most of it motorway miles). The motorway journey is the only thing that will clear the problem as when city driving it just stays as a problem and the motorway drive will always sort it out

 

No doubt your car has had the emissions fix, mine was regenning every 180kms if not less, I could do an 800km motorway journey pulling a massive air brake of a heavily overloaded trailer, large throttle opening, WOT on all inclines, a non stop 800km passive regen yet it did 4 or 5 active regens during the journey and started another one the very next day which did not conclude and it was trying again on every journey, the software engineers who did the programming for the emissions fix recall were clowns, I have paid to go back to the software revision programmed by cheats!

 

I have been aware of 2 interrupted regens in 18 months and 25K miles since the roll back and they successfully concluded on the next short journey, its basically unnoticable as it was intended and as my old neighbours car which has never had the update is.

[chimaera]

42 minutes ago, J.R. said:

 

No doubt your car has had the emissions fix, mine was regenning every 180kms if not less, I could do an 800km motorway journey pulling a massive air brake of a heavily overloaded trailer, large throttle opening, WOT on all inclines, a non stop 800km passive regen yet it did 4 or 5 active regens during the journey and started another one the very next day which did not conclude and it was trying again on every journey, the software engineers who did the programming for the emissions fix recall were clowns, I have paid to go back to the software revision programmed by cheats!

 

I have been aware of 2 interrupted regens in 18 months and 25K miles since the roll back and they successfully concluded on the next short journey, its basically unnoticable as it was intended and as my old neighbours car which has never had the update is.

Towing a 1.4 tonne caravan, I've gone 400 km between active regens if VAG-DPF is to be believed. In normal driving (mix of urban and motorway) it goes 150-200 km between active regens. Ten minutes and it's done.

[J.R.]

Allowing for my involuntary exaggeration mine might be the same, I dont have VAG-DPF and being partially sighted would not want to look at a phone screen while driving so I rely on VCDS to tell me how many kms since the last regen and I look at the calculated figure compared to the threshold limit, the measured figure was always next to nothing which was what really peeved me off.

 

So it could have regenned twice on the journey and then again at the end, my 180kms estimated fits with yours but that was far too frequent given the measured values never ever got above 3 units compared to the estimated of 25.

 

My journeys at this end are either less than 10km each way or once or twice a week 20km = 20 minutes, the engine was only ready for the regen after say 12 minutes meaning they would not complete unless I did extra miles, 10 minutes of the proper conditions was always enough for a completed regen.

[Ootohere]

The OP says there is a problem and says why.

 

But apparently there is no problem just the car doing what the car does.    So really not that complicated.  

[3T51704x4]

The fan normally comes on when the A/C is on to cool the condenser. Try turning it off and see if the fan stops. It can also be commanded on if a fault is logged in word 01.

DPF will not regenerate until the exhaust gas temperature sensors start to read above a few hundred degrees C, with an engine check light on, with fuel below around 1/4 tank or accelerating hard.

If you have low usable charge in your battery, it can jack the idle speed up, like the others have suggested, check the owners manual for detailed info.

To see if the battery is low (as the car sees it) Check in word 61 for early cars and word 19 for later cars. Look in live data (measured value blocks) you will fine usable charge in Ah. Compare that to the rated Ah printed on the battery to see how much capacity you have in reserve. It is also possible to see the current the battery is taking to charge. A flat battery taking only 1 or 2 amps is worn out. A flat battery taking 30A and above is healthy, lots more useful info in there.

Anyway I use a piggy back device connected to the gateway to get my cars basic engine info in the DIS, some of the pages shown in the images below.