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I bought a used Volvo V40 (2002). It worked great for about two weeks, after which the central locking stopped working. The FOB doesn't do anything, and each door has to be locked and unlocked separately like back in the old days. The worst thing is that the passenger-side doors are completely locked and I can't open them at all.

Anyway, I suspect the problem lies either in the relay or the central locking control unit. How would I know which one is it? I already checked the fuses and they're all OK.

I know where the control unit is located (under the CD player) and is seemingly easy to take out and replace, but they're not really available anywhere. I personally suspect the relay more since there's no relay clicking when the locks are used. However, I don't know which relay it is or where it's located. I also couldn't find any "central locking relays" in the local shop's catalog - I hope it's a standard relay you can buy anywhere.

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  • Did you check all the fuses too? – JPhi1618 Mar 18 '16 at 17:43
  • And you know for sure the fob is working? – Pᴀᴜʟsᴛᴇʀ2 Mar 18 '16 at 21:23
  • @JPhi1618 Yes, I checked the fuses and they're all fine. – manabreak Mar 19 '16 at 5:43
  • @ᴘᴀᴜʟsᴛᴇʀ2 The fob might or might not be working, but the central locking should work with the key or with the lock button as well. – manabreak Mar 19 '16 at 5:43
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There isn't a mechanical relay it's all controlled by the Guard Lock and Alarm module.

Gain access to the module and test for power on pins A26 (green/red) B1 (red) and B8 (white). Test for ground on pin A1 (black)

If you don't have power on those pins check fuses 7 & 8 in the under dash fuse box. And fuse 9 in the engine compartment fuse box.

If you don't have ground in the left kick panel there should be a ground splice.

If you have power & ground at the module check pins B2 (gray/white) and B12 (green/gray) for output when pressing a lock switch. I believe gray/white will be power and green/gray will be ground.

If there isn't any output likely the GLA module is bad and needs to be replaced. This may be rare.

You can check the switches by pulling the driver switch and checking for ground on pin 2 (black) and when pressing a switch ground on either pin 1 (brown/gray) or pin 3 (yellow/gray). And checking pins A16 & A18 at the GLA module.

Most likely you're going to have a fuse or wiring issue.

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  • Wow, thanks for your answer! I've checked all the fuses and they're all fine. It'll be another week until I get to check the pins and the wiring, but this will definitely help. I'll let you know how it ends. :) – manabreak Mar 19 '16 at 5:40
  • I checked the wires, and A26, B1 and B8 all have power. B2 against B12 is zero when ignition is off, and constant when ignition is on. The unit itself doesn't have any visible burns or anything. – manabreak Mar 28 '16 at 13:14
  • @manabreak What happens on pin B12 when you press a switch? It should ground the lock actuators if the switches/module is OK. You should also check pins A16 & 18 (driver switch pins) for ground when the switch is pressed while you're at the module. – Ben Mar 28 '16 at 22:25
  • It was a tad difficult to hold the pins and press a switch, but as far as I was able to check that, nothing seemed to happen. I found a cheap unit that was taken out of a crashed Volvo so I'll check with that unit as soon as I get it. Meanwhile, I'll try to check the A16 and A18 tonight. – manabreak Mar 29 '16 at 5:44
  • @manabreak pick up some sewing pins from a hobby shop and some alligator clip test leads that way you can easily backprobe connectors and test switches and stuff. – Ben Mar 29 '16 at 12:43

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