A4 Avant B5 LHD - Battery Drain

[jwsmith2015]

Hi Guys,

My A4 Avant B5 has a problem with the battery regularly going flat, I have observed the following:-

When the fault is there and a with fully charged battery, all doors closed, interior lights off, bonet latch 'frigged' closed, an ammeter is then introduced into the circuit without disrupting current flow there is a current drain of greater than 2A (my meter has a max rating of 2A).

Upon removing the meter from the circuit an audible click is heard, it sounds like a relay dropping out. After a 10 sec delay the meter is then reintroduced completing the circuit, the current starts off at around 0.25A and after a few seconds drops to around 0.050A.

The battery may be in a poor condition now after periodically going completely flat but it is only 2 years old. The other thing I have noticed is that the charge voltage, even with a charged battery is only 14-15v (I would have expected around 17v).

So there may be a duff battery and a voltage regulator issue, but I'm concerned about the current drain when the car is just stood.

There is another thing that may or may not be related, sometimes after starting up the dash instruments are dead with rev counter and speedo not registering, then after a few minutes the dash bursts into life, usually flashing on/off several times before settling down leaving the trip counter reset to zero.

Sorry for the long saga, any help would be greatly appreciated.

John

[scootermap]

Sounds a lot like my problem check to see if you have had water in your computer area lh side below windscreen,I found that there had been water in and had 2 rotten relays,this made the fuel pump use power when switched off.I also got a flashing heater plug light.
I replaced the relays and a new comp compartment cover and it solved the problem.
cheers
Graham.

[jwsmith2015]

Hi Graham,

I have seen relays mounted behind the fuse panel, this is on the drivers side on my left had drive model, but I haven't seen a computer module (my A4 Avant B5 is a 2000 model), am I looking in the same area?

John

[scootermap]

Good morning John mine is also a LHD 2002 strangley enough.
The relays that I am talking about if its the same are under the bonnet if you look in your right hand corner facing the car just below the bonnet you have to remove the windsreen scud panel as its called and then you have a square panel with hi torque fasteners in,beware as a couple of the fasteners are hard to get under the windscreen area.When this panel is removed if it is the same as mine you will then reveal the computer,just below the computer are some relays look to see if there is any evidence of water damage ,check all the relays and replace if nessesary.
I had a read out done and it said that my fuel pump was faulty but the reality was that the relays were rotten and not shutting the systems down.
I hope this makes a little sense if not done hesitate to ask any questions.
good luck
Graham.

[jwsmith2015]

Thanks Graham, I'll have look and report back.
John

[jwsmith2015]

Hi Graham,

Unfortunately the ECU box and relays were as dry as a bone. I tried a few more tests but the fault seemed to have disappeared. I'll have another go when I get some willpower back.

If I find anything more significant I'll post it to you.

Regards

John

[s1turbomike]

Hi John

If the drain comes back, have you tried with an amp meter on it, pulling a fuse out of the fuse box one at a time? I would do this with a fully charged battery, all the doors opened but the catches locked and then by locking the car with alarm. leave it for around 5 mins to allow the dash display to go out. the max i would recommend for the drain would be 50 milliamps/0.05amps any thing higher is excessive. The car should when running charge at between 13v to 14.5v. If it is higher than this then there is a fault with the regulator.

Hope this is of any help.

[jwsmith2015]

Hi Mike,

Thanks for that, I will get hold of a ampmeter that will read greater than 2A and the do as you suggest. I will contact you with the results.

Regards

John

[delta925]

Charge voltage should be around 14.4V.

17V would boil battery as well as blowing all your bulbs and other electrics.

[jwsmith2015]

Well gentlemen, I think I’ve found the problem.

There was a missing bit from the puzzle that I forgot to mention, there was an intermittent problem with the front passenger door (LHD Avant) where upon closing left the interior lights along with the red door lamp on a slow flash, this fault eventually stopped when the door lamp failed.

While investigating the battery drain fault I replacing the lamp and the fault reappeared, so biting the bullet I removed the door trim and investigated, everything looked ok but on following the wiring harness as it emerged from the flexible hose into the door cavity it passed over an unprotected 4mm stud attached to the door frame about 30mm below where the harness entered the door and the harness was rubbing right over the top of the stud.

I couldn't feel any damage to the harness however it fitted the bill directly, I fitted a plastic sleeve over the stud and so far no flashing interior lights and no battery drain faults.

I do still have a problem with my dash instruments however, this seems to get worse with cold weather and as the rev counter, speedo, fuel and temperature gauge are all affected I'm suspecting a dodgy earth point in the dash area.

You guys out there have been extremely helpful with my previous issue - can anyone help with the location of this dash earth point.

All the best,
John

[j7uga]

hi I have a q7 had same problems changed 2 new batteries changed relays and still was causing may new baterie to go out off power the one day I decided to switch off the auxiliary heather on the car and my problems are now gone no more problems with batterie hoppe it helps you