PLease help. I have a volvo S40 2000 model. Central lock suddenly failed completely. All was working fine then suddenly after a ride it completely stopped working. completely meaning its as if there's no power going to the system. Not even from the dashboard button. I have to do everything manually by key. And with the key it opens manually; just that lock of that door goes up, as if there's no central locking at all. The fuses are all ok. What could be the problem?

SOURCE: REAR DOOR LOCK

you either have a faulty central locking motor or the wiring harness may be damaged.
Remove the door panel and check if you have a live feed to the central locking motor when you use the fob to lock or unlock. If you have power, then it will most likely be the motor that is at fault.

SOURCE: My central locking was working

Hi Pirates901.
The most likely cause is a faulty Central Locking Pump. I had this problem recently and it is apparrently quite a common fault on the A4. When you use the key manually can you hear a kind of humming noise for about 20 seconds or so coming from the rear of the car? If you can it indicates that the pump is trying to open the doors but something is preventing it.It might just be a leak in one of the air hoses but more than likely the compressor wheel inside the pump has disintegrated. I posted a solution to this the other day so I will just copy/paste it here for you.

There are 2 ways of solving it. The first is to pay your Audi Service Centre £350-£550 to replace it for you and the second way is to do it yourself which will cost well under £100 (depending on ebay). Firstly check the Central Locking Pump to make sure the hoses haven't come off. This is located in the very back right hand corner of the boot so you will need to remove the carpet and internal trim and you will see a block of sponge. Carefully lift the top off this and you will see the pump sat inside it.
Actually there is a great set of photos online to help you and I will add the link for you at the end. If the hoses are still connected and not leaking it is very likely that the internal compressor wheel has shattered (quite a common fault). I believe it is possible to open the pump and replace this wheel (in fact there is one for sale on a very popular auction site at the moment) but my own preference was to simply buy a whole new pump and replace that (£16.00 + £8 p+p off the same auction site).
The most important thing for you to remember is that when you look to buy a replacement pump you need to find one with the EXACT same serial number. The one in the diagram shown is
8LO 862 257 N but I have a sneaky feeling yours might end in an A.
Anyway, I hope this is of some help and dont worry about the connections as both air connectors and all 3 electrical ones are different sizes and will only fit in one place each.
Good luck.
Rik

http://www.audiworld.com/tech/elec131.shtml

SOURCE: Volvo S40 OBD II P0171 & P0237

for p0171 it could be a few things like intake/exhaust leak,air system,map/vaf sensor,fuel presure/pump,injector(s),ho2s(heated oxygen sensor.

Paul W

• 404 Answers
• Posted on Jan 18, 2009

SOURCE: Maintenance light reset

Hi,
I've reset this particular model I held down tripmeter button turned on ignition whilst still holding it down for 20 seconds at least then Bingo sorted.
If unsure hold all buttons on speedo face down.
Good Luck!
Paul 'W'
Onyer~EDson(:0) {#><U.K.

SOURCE: volvo s40 1998 bulb warning light on, what does

If by that you mean:

"warning light goes on when I start the motor, and goes off after first time I use the brake pedal"

, don't worry, it's normal, it's how it work. If it stays on even after the use of brakes, you have a bad bulb on brake tail lamps