v40: remote locking FOB stopped working

norbertm · Nov 28th, 2017, 23:50

Remote (un)locking by FOB stopped working at my 2002 V40 from one day to the other.
Investigation of the problem showed that the RF receiver module (behind/above main control panel) is working properly. At least I was able to see demodulated bitstream using an oscilloscope when pressing FOB keys.
After some testing I found following strange behaviour:
After dis- and reconnecting car's battery the remote doorlock works exactly one time! Then ceases to work anymore and I have to (un)lock manually using key.
Dis- and reconnecting plugs of "Lock Alarm Control" module yields same as the temp. battery removal: remote locking is working exactly once. Same game with temporal fuse removal.

Central locking itself works fine -- although locking by key requires some force. Unlocking is easy, the motor supports instantly.

Does any of you Volvo experts have an idea?
Best regards, Norbert.

CharlesStevenson · Dec 6th, 2017, 00:45

Obvious question: have you tried putting a new battery in the fob?

Ours was needing to be closer & closer to the car and then died about a wk ago.

One trip to Tescos for a new battery and it's arming / disarming from via the house's window.

If in the period immediately prior to it not working you'd been having to be close to the car to arm or disarm, this could be the 'fault'.

Just suggesting ...

trufauru · Dec 6th, 2017, 21:12

I was going to sugest the same as CharlesStevenson

My fob was starting to fail, and it was getting harder to open the car. I changed the battery (not easy to find over here) and everything was working as it should.

norbertm · Dec 27th, 2017, 15:12

Thank you for your suggestions, but unfortunately new batteries didn't resolve the problem.
As both FOBs seem OK. But car will open/close exactly one time after power-cycling: Remove fuses or battery or connectors from doorlock electronics module (in middle cosole, below radio/climate). Afterwards no reaction anymore.

Perhaps some out-of-sync ?

CharlesStevenson · Jan 1st, 2018, 20:57

That does sound odd - Sorry about that as the batteries would have been a great quick-fix.

I don't have any better suggestion that to try searching back through some old posts on here (you're probably not the 1st to have suffered this problem).

Hopefully you'll find an answer.

A thought: do all the door buttons go down and up freely? Perhaps one's jammed & causing the issue? When we got our S40 the c/l wouldn't work via the fob, but I realised that the driver's button had been forced down and was "out of sync". I pulled it up with a pair of plyers and then after a few lock-unlock cycles all was well.

Just suggesting, but you've probably tried all the quick-wins already.

canis · Jan 2nd, 2018, 11:56

I believe they use revolving codes, otherwise anyone with an infra-red electronic "eye" could record your signal when you lock your car, and then retransmit it when you're out of sight. This probably explains why it works only once. Presumably the car and the fob are revolving their codes non-identically.

Perhaps if you power-cycled both simultaneously? I'm guessing though, don't know for sure.

Nov 28th, 2017, 23:50	#1
norbertm New Member Last Online: Dec 27th, 2017 15:21 Join Date: Jun 2015 Location: Garbsen	v40: remote locking FOB stopped working Remote (un)locking by FOB stopped working at my 2002 V40 from one day to the other. Investigation of the problem showed that the RF receiver module (behind/above main control panel) is working properly. At least I was able to see demodulated bitstream using an oscilloscope when pressing FOB keys. After some testing I found following strange behaviour: After dis- and reconnecting car's battery the remote doorlock works exactly one time! Then ceases to work anymore and I have to (un)lock manually using key. Dis- and reconnecting plugs of "Lock Alarm Control" module yields same as the temp. battery removal: remote locking is working exactly once. Same game with temporal fuse removal. Central locking itself works fine -- although locking by key requires some force. Unlocking is easy, the motor supports instantly. Does any of you Volvo experts have an idea? Best regards, Norbert. Last edited by norbertm; Nov 29th, 2017 at 01:36.

Dec 6th, 2017, 00:45	#2
CharlesStevenson Premier Member Last Online: Mar 24th, 2024 17:33 Join Date: Nov 2000 Location: Nottingham	Obvious question: have you tried putting a new battery in the fob? Ours was needing to be closer & closer to the car and then died about a wk ago. One trip to Tescos for a new battery and it's arming / disarming from via the house's window. If in the period immediately prior to it not working you'd been having to be close to the car to arm or disarm, this could be the 'fault'. Just suggesting ... __________________ Now: 04 reg V70 2.4 SE 2.4 auto 177k Then: Volvo, Saab, BMW, MB, Ford, Vx, Opel, Fiat, Rover, Porsche, Alfa, Austin, Renault, etc

Dec 6th, 2017, 21:12	#3
trufauru Junior Member Last Online: Aug 13th, 2020 19:29 Join Date: Apr 2017 Location: Montevideo	I was going to sugest the same as CharlesStevenson My fob was starting to fail, and it was getting harder to open the car. I changed the battery (not easy to find over here) and everything was working as it should. __________________ Current Cars Volvo V40 2001 - Daily Duties Toyota Corolla 1974 'TE27' - Restomod in progress Audi 100 1973 - Trying to get it on the road UAZ 469 2002 - Beach/Surf Duties

Jan 1st, 2018, 20:57	#5
CharlesStevenson Premier Member Last Online: Mar 24th, 2024 17:33 Join Date: Nov 2000 Location: Nottingham	That does sound odd - Sorry about that as the batteries would have been a great quick-fix. I don't have any better suggestion that to try searching back through some old posts on here (you're probably not the 1st to have suffered this problem). Hopefully you'll find an answer. A thought: do all the door buttons go down and up freely? Perhaps one's jammed & causing the issue? When we got our S40 the c/l wouldn't work via the fob, but I realised that the driver's button had been forced down and was "out of sync". I pulled it up with a pair of plyers and then after a few lock-unlock cycles all was well. Just suggesting, but you've probably tried all the quick-wins already. __________________ Now: 04 reg V70 2.4 SE 2.4 auto 177k Then: Volvo, Saab, BMW, MB, Ford, Vx, Opel, Fiat, Rover, Porsche, Alfa, Austin, Renault, etc Last edited by CharlesStevenson; Jan 1st, 2018 at 21:00. Reason: remembered what I'd forgotten initially

Dec 27th, 2017, 15:12	#4
norbertm New Member Last Online: Dec 27th, 2017 15:21 Join Date: Jun 2015 Location: Garbsen	Thank you for your suggestions, but unfortunately new batteries didn't resolve the problem. As both FOBs seem OK. But car will open/close exactly one time after power-cycling: Remove fuses or battery or connectors from doorlock electronics module (in middle cosole, below radio/climate). Afterwards no reaction anymore. Perhaps some out-of-sync ?

Jan 2nd, 2018, 11:56	#6
canis Non Fragile Last Online: Oct 13th, 2023 05:46 Join Date: Apr 2010 Location: Chadderton, Oldham	I believe they use revolving codes, otherwise anyone with an infra-red electronic "eye" could record your signal when you lock your car, and then retransmit it when you're out of sight. This probably explains why it works only once. Presumably the car and the fob are revolving their codes non-identically. Perhaps if you power-cycled both simultaneously? I'm guessing though, don't know for sure.

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