Solved: Volvo Guard 1 remote C/L range.

[James_EG_940]

Hi all,

I've been holding off on posting this for a few weeks because I didn't want to claim something without thoroughly testing it but I think I might have solved the problem that Volvo Guard 1 systems have with their remote range deteriorating over time.

My remote fob was intermittent at best, non functional at worst and usually required that you hold it right up to the windscreen near the triangle on the A pillar. However for the past month or so it has consistently worked every single time I have used it and the range has increased to certainly >10m.

The best part about this fix is that I only used a screwdriver to achieve it.


** You can skip this next bit if you just want the fix and don't care about how the system (probably) works.

With some speculation, what follows is how I believe the system to work.

So the system works by your keyfob repeatedly sending out a unique code when you press the button and it sends this out over a very specific radio frequency; 418.05MHz to be precise.

The receiver in your car then acts as you might imagine a regular radio would, it is tuned in to listen to signals in a very specific band. Much as you would need to tune your radio to, lets say, 97.9MHz to hear Radio 1, your alarm system is tuned to 418.05MHz to listen out for any unique Volvo Guard codes it can 'hear'.

Doing some digging into the component inside the keyfob that generates that 418.05MHz frequency I found that a) it is no longer made and there is no suitable replacement and that b) time since manufacture and temperature affect how accurate the frequency it produces is. So, a 20 year old keyfob may no longer be able to send its codes out on 418.05MHz, it might now be sending them out on 417.55MHz or 418.55MHz.

This would explain why the fob's effectiveness deteriorates rather than simply stops all together. If we go back to our Radio 1 example, you could slightly detune your radio and still be able to hear Radio 1 but it might be a lot less clear and probably has lots of static etc.

So, we have two possible solutions. Either 1) we could replace the degraded component. (they aren't produced anymore but can be found as n-o-s, I have 4 sat on my desk right now, but I have not tried replacing one to see if it makes a difference) or 2) we could retune our receiver to 'listen' on the new frequency.

I have found that by simply retuning the receiver my ailing and old VG1 alarm system has been given a new lease of life; once again I can scare passers by by locking and unlocking my car from stupid distances!



** The fix

Taking a small flat head screwdriver, like an electrician's screwdriver, gently pop off the cover of the black triangle on the A pillar. There is a tiny amount of glue to defeat but the cover snaps into little notches in the backing so will not need regluing. This is relatively easy but can be a little delicate, so some patience is required.

Once the cover is off look closely at the uppermost corner of the circuit board underneath, you should see a small blue (or possible some other colour) square component with what looks like a + (plus) sign inset into a white circle on the top.

This component is probably covered in a layer of lacquer but it is easy enough to gently chip off with the corner of your screwdriver blade and is probably just there to stop things moving over time.

Once you have most of this off, turning the + section will basically tune your alarm receiver. Make a note of exactly where it is before you move it, just in case you need to put it back. I found that rotating it anti-clockwise 1/4 turn was all that was needed to make my fob work again, turning it further than this or clockwise made it perform noticeably worse so a bit of trial and error may be required to tune it to your particular fob.

That's it! Once you have tuned it and checked that you get a better range and it all works etc. snap the cover back on and you're done.

Like I say, mine has been working faultlessly now for over a month since I did this, so I'm pretty sure (despite speculating a lot over the reasoning) that this might have cured it. Which is great, cause it sure as hell annoyed me and I'm sure it would make other people's remote central locking a bit more functional. Even if there are only about 7 of us with VG1 alarms left!

[Forrest]

Thanks for a useful write-up which I might try when I am feeling brave enough to try to pop the top off the receiver on the A-pillar.

If your theory is correct, I wonder if it is actually the receiver that goes out of tune over time rather than the transmitter. The reason I say this is that when mine first failed Volvo still sold the grey single-button fobs and I bought two brand new ones from the dealer. Annoyingly, they behaved in exactly the same way as the originals.

[James_EG_940]

Given that evidence, you could well be correct Forrest but I have no way of proving it either way. My contradictory evidence is that I have two fobs from separate cars and are slightly different inside (same component that generates our 418.05MHz frequency though) and one has a noticeably shorter range than the other. My main fob will work from my kitchen at the back of my house to the car parked on the street at the front. That's about 15m through 3 solid brick walls and a row of trees.

There are many electronic components that will degrade over time although capacitors in particular are definitely high on that list and old fashioned radio tuners were in fact variable capacitors...

I need to take a couple of pictures on my next day off to really round off the article but I have also added a massive aerial extension round the entire headliner of the car (predates discovering this "tuning" method) and with pictures I can illustrate where to solder it onto the receiver.

[Clan]

Originally Posted by Forrest

Thanks for a useful write-up which I might try when I am feeling brave enough to try to pop the top off the receiver on the A-pillar.

If your theory is correct, I wonder if it is actually the receiver that goes out of tune over time rather than the transmitter. The reason I say this is that when mine first failed Volvo still sold the grey single-button fobs and I bought two brand new ones from the dealer. Annoyingly, they behaved in exactly the same way as the originals.

yes there was a known problem with the receivers for lack of range , Volvos cure was to fit a new receiver complete .

[TonyS9]

Interesting work. I was fairly certain the problem occurred at the receiver as outside temperature and humidity affected it. A check with a spectrum analyser should give an idea.

Given the effect of humidity I expected there would be some corrosion or electromigration but noone has found any yet. I shall have a go sometimes and your tuning issue is a good start. I also have access to some rf equipment.

BTW electrolitic caps degrade because they dry out, a variable cap will be a dry type, it should not degrade although humidity might affect it more. Other types are more reliable but mechanical stress can cause temperature related changes.

[Forrest]

With the (slightly) warmer May weather I decided it was time to try this fix and I can confirm it works exactly as described.

I used a flat bladed dinner knife gently to pry the cover off. The insides were as described, even down to the dry glue covering the potentiometer screw - top right in my second picture.

Both fobs are now working from a decent distance for the first time in about ten years.

[Clan]

Originally Posted by Forrest

With the (slightly) warmer May weather I decided it was time to try this fix and I can confirm it works exactly as described.

I used a flat bladed dinner knife gently to pry the cover off. The insides were as described, even down to the dry glue covering the potentiometer screw - top right in my second picture.

Both fobs are now working from a decent distance for the first time in about ten years.

These remotes have the greatest range of any volvo remote when working properly , if you can see the car the remotes should work

[TonyS9]

Finally got around to doing this, and pleased to report it works for me too. Cover popped off quite easily, removed glue from the screw in the blue component and a tweak anti-clockwise as little as I could turn it while holding the fob about 1m away. Working well now 10m+, before was right up on the windscreen.

[rogerthechorister]

Wonderful explanation - but my system seems to be different.

My 940 remotes have two buttons. Am I to infer that they are a different system?

On one car they work OK although range is pretty short.

On the other - totally nothing. Yes I have changed the batteries.

What do I do next?

[TonyS9]

Yes the post assumes you know the difference between guard 1 and 2. AFAIK this is only relevant for Guard 1 (grey singe button remote), however the same type of thing may apply to guard 2 but I couldn't say where the receiver is exactly. There is a controller of some sort behind the glove box below the A pillar.