I have a 2002 A6 c5 2.5tdi with 344k on the clock and thought I'd do a buyer's guide. My A6 has full service history and I'm the second owner. My dad being the first owner. The engine and gearbox have never been rebuilt. 

What's the service history of the car? 

Check when Cambelt and water pump was last changed.asbrgis is a front of the car off job. Should be done at least every 8 years. 

Do all electrical items work? 

AC compressors can fail and they're expensive to fix. The central LCD screen pixels are known to fail but these can be replaced for around £300 roughly. 

Also I appreciate Spain doesn't get as much rain as the UK but water ingress culprits include the pollen filter housing and the battery tray which is located on the scuttle panel. The tray fills with leaves etc blocking the drains. These spots let water in and flood the comfort control module situated under the carpet (passenger side in rhd cars). The CCM failing can cause all sorts of electrical gremlins. And has to be replaced with a part with identical part number. 

If an auto and a CVT make sure it changes smoothly as these gearboxes are prone to failing. Make sure it's been serviced. 

Slow starting can be caused by failing glowplugs. I can confirm this engine can start with only 3 glowplugs working! As I found out. 

Smokey exhausts can be caused by leaking injector seals. 

Headlight switches have been known to catch fire and I believe there was a recall for this however facelift cars should be fine. 

I personally am finding it hard to source interior trim. You might have more look in LHD. 

As with any diesel the turbo can fail and they can whine. My car has had 2 turbo's in it's 20 year 344k life. The first turbo failed at just over 70k. 

These engines do have egr valves. These valves are known to fail on modern diesels but In my case (fingers crossed) it's still on its original egr valve. 

Knocking noises from the front can be engine mounts. Also on the front suspension arms are known to go. 

Bodywork issues are the top of the front arch lips due to the cars having a piece of foam on the inside which obviously absorbs moisture and causes the wings to rot, and bubble all round the arch edge. Also check lower does where the lower door trim is as rust can form under this trim. You'll know if you look on the inside of the door in the corner. Also l the headlights may have been affected by the sun and gone cloudy. 

Over all they're great cars I still use mine for road trips around the UK and Europe. It's due to go to Norway and the arctic circle in August 2023!

On the whole it's been reliable despite going round the nurburgring, drag strip at Santa Pod plus maxing it on the autobahn. Obviously I've mentioned some issues, of which I've had a few of the ones listed. 

A lot of people slag off the 2.5tdi as being unreliable, however I believe the unreliability comes from a lack of good maintenance and poor servicing. Mines over serviced to be honest but I want it to be on best form.as possible and for my peace on road trips. 

Just remember the car might be cheap to buy but no matter how old an Audi gets the bills remain high. 

Oh and don't forget to check out the A6 c5 section on this forum as it'll give you further helpful advice 🙂

I am thinking of buying a 2004 Audi A6 avant with 165k miles ....1.9tdi (130bhp).

I had a 2008 2.0tdi A6 avant 6 speed manual and regret selling it.

The 2004 A6 Avant 1.9tdi has had a lot of money spent on it in the past 12 months front brake calipers, discs and pads.

Full service oil, oil filter, diesel filter, air filter, pollen filter.

Cambelt, tensioners, water pump. Coolant, egr valve, shock absorbers front and rear.

As its an automatic it's had the gearbox serviced twice once at 70k miles and once at 140k.

It's dark blue and has a tan leather interior.

Air con has been serviced and works well. My only concern is the auto box.?

Should I bite the bullet and buy it..the owner is asking £1850 no offers.

What do I need to look out for?

Cheers Nomi64

 

 

Make sure all electrical items work.  Make sure carpets either front or rear aren't damp as water ingress is common and can't damage the ccm. Make sure gearbox changes are smooth. 

Thanks for the guide. I picked up a C5 Avant (2.5 diesel) recently and it has been great so far. It looks to be quite an unusual spec too. I have noticed that the gearbox (tip tronic) likes to hold all of its gears. It refuses to go into 5th until i hit 40mph. Likewise, it will not go into 4th until I'm doing at least 30 and 3rd when im doing 20. Is this normal? The car has done 135k and I don't see anything in the service history that it has had its oil renewed, so I take it it is overdue for a gearbox service.

Also, the Turbo has a faint 'whistle' to it (like an owl) when accelerating like you mentioned. I quite like it actually, but is this just a feature of this engine or a sign that it is worn? thanks.

You're welcome glad the guide was useful. I'd recommend a gearbox oil service to see if that solves the gearbox issue. I suspect though it's a megatronics unit failure. I'd recommend a diagnostic check to see if any fault codes flag up. 

 

there dont seem to be any transmission related warnings in the diagnostics apart from "17087:35" which relates to torque converter brake switch malfunction and is intermittent. A quick google search confirms it relates to the brake pedal switch that tells the gearbox the brake is depressed. Clearly not anything to do with the issue I've noticed.

I think its just due a good 'ol gearbox service which I'll do asap.

1 hour ago, WillC9303 said:

there dont seem to be any transmission related warnings in the diagnostics apart from "17087:35" which relates to torque converter brake switch malfunction and is intermittent. A quick google search confirms it relates to the brake pedal switch that tells the gearbox the brake is depressed. Clearly not anything to do with the issue I've noticed.

I think its just due a good 'ol gearbox service which I'll do asap.

Keep us posted on how you get on 

Would I be wrong in thinking the quoted gear change speeds seem reasonable? 
Regards,

Gareth.

To my mind the road speed (mph) when gear changes occur don't tell us as much as engine speed (rpm). If the engine is revving above about 2000 rpm under gentle acceleration before changing up I would suspect a fault. The most likely thing is the mechatronic control unit within the gearbox which is known to be troublesome after a great mileage.