A6 Avant 53 plate "Vacuum Pump" recurring fault

[wilsongrim]

Hi all

I have a recurring Vacuum pump fault, however the garage have checked out the pump and it appears to function OK as does the associated non-return valve.

Due to the lack of Haynes, or similar, manual for this model I find it difficult to work on the car myself, I am also unwilling to pay my local dealership to keep their mechanics in gold-plated tools and Gucci overalls (£150 to change the oil in my gearbox of which only £50 was for the actual oil!).

I do not have the equipment to read the codes myself, but I believe that it is the same as the "17887/ p1479/005241 - brake boost vacuum system: Mechanical failure" that comes up.

Associated with this, I think, is the fact that the vacuum is not being held by the servo (i.e. the brake pedal is hard first thing in the morning before starting the engine, previous cars I have had retained some vacuum in the servo system overnight so there is a soft pedal even before starting the engine).

Is there a common fault that would cause this? Otherwise I'm guessing that the vacuum hoses, the sensor which raises the fault with the ECU or the servo is at fault.

I am in the Lytham St Annes / Fylde Coast area of Lancashire, UK. Can anyone recommend a good independent specialist in my area.

Thanks for reading, I would appreciate any thoughts you may have.

As a supplementary question, my A6 is a 2.4 Petrol with Multitronic box (it does not appear immune to the multitronic problems and jerks once in a while, in reverse only).

My question is simply this, what sort of real world fuel consumption should I be seeing and how accurate is the readout on the dash, should I be brimming the tank and clocking the miles the old fashioned way?

I currently get around 27 on my 14 mile a day commute but less than 33 on the motorway.

Thanks

Grim

[iwaters]

Sounds to me like you may have a split hose between the servo and the pump. Check these carefully.

Can't help with a recommendation in that area I'm affraid.

I have the same engine as you and a multi. I get about 17 MPG around town with a heavy foot. Motorway I get around the 35 mark if I keep to the NSL (who doesn't ). I used to commute about 30 miles mixed road and could get it as high as 36 with careful driving.

Thats a littl ehigher than you are seeing. Could be down to driving styles. Whats the service history like on yours? Might just need some new plugs and filters.

[Peter D]

Please provide the engine code from the ID label in the spare wheel bay. Is you plenum chamber retaining water ( down the side of the battery.) Regards Peter

[Peter D]

The message "brake boost vacuum system: Mechanical failure" refers to a mechanical pump as per the deisel, you have an electrical pump with a vacuum sensor and the electric pump is controlled by a relay which also may be a cuse of your problem. Do you actually run out of vacuum for the brakes with your foot off the throttle. Regards Peter

[wilsongrim]

Thanks for the prompt replies, to answer the questions both have asked:

Although the service history is a little patchy, the last service (about 4,000 miles ago) was carried out, at great expense, by the local Audi dealer (Preston Audi) the fault light has become apparent since then. I don't know about the servo not retaining vacuum, I didn't notice until it was suggested I check!

Engine code is BDV and transmission is FRY

I haven't checked the plenum chamber yet, will look later.

I have not yet run out of vacuum at any point whilst driving.

The fault code according to my garage definitely mentions "Mechanical Failure" which is why I suggested it was similar to the "17887/ p1479/005241 - brake boost vacuum system: Mechanical failure" unfortunately searching the forum I have not been able to find a post that matches my problem more closely.

Grim

[Peter D]

I suspect this is a vacuum sensor fault. Remove the black plenum cover and you will see the sensor on the pipe. Regards Peter