Ever felt being a wally? Wondered what you did wrong?

So, I'll set the scene.

You of course have fully read and inwardly digested your Croma (other) owner's handbook, especially the section about the remote not working.

So it happened to me.

Zimples!

You try remote nearer the car, under the wheel arch, in the windscreen etc. Try all remote buttons incase one was duff.

Now you resort to the emergency key. Yes you remember that your remote fob contains a mechanical key that you can use. You lift the door handle, find the lock, insert and turn......nothing! You now try clockwise and anti-clockwise....nothing again. Bang / shake the fob and try remote again. Nothing. But the led on the drivers door is blinking so there must be some power in the car.

Call wife, bring spare key. Bingo and return home. When you get home the once duff remote is no longer duff and battery checks out OK.

Where for me it all went wrong was the emergency mechanical key usage. I was expecting some reaction from the car door locks when I inserted and turned the key. WRONG.

Firstly the manual is wrong. It suggests an anti-clockwise key turn. For me it was clockwise. Also a rather null, dead, etc. operation and feel, almost like you are forcing something that was never there.

In addition, and this is the killer, having had no obvious response from the emergency open operation when you get home and play you find that you have to remove the key, drop the door handle fully home and THEN, and only then, lift the handle again.

I initially thought that because I had set the deadlocks that this was fully locking me out. WRONG!

I strongly recommend all you Croma owners go and play at "emergency key entry" so that if you ever need to do it for real you know what to expect and how to do it properly.

NOTE! On entry the car alarm will go off! I've cancelled this with the remote to not upset the neighbours. I'm hoping / guessing that once you are in the car, with the alarm going off, that inserting the fob/key into the console and turning the ignition on will cancel the alarm. Next time I'm in a remote area/car park I'll check this out (unless someone beats me to it).

Sounds like a right pain.

Perhaps preventative action might be the way to go - replace the battery every few years before it dies. Maxell CR2032 batteries are from 99p delivered on ebay, less if you buy more at once.

Doofer said:

Sounds like a right pain.

Perhaps preventative action might be the way to go - replace the battery every few years before it dies. Maxell CR2032 batteries are from 99p delivered on ebay, less if you buy more at once.

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Well I now have a spare battery in the glove box dated 2018. Assuming come 201x I can remember the fiddle of the emergency key procedure I should be able to get into the car and use the new battery.

As for battery life I should have realised that my battey was ok and it was most likely a dirty connection. I panniced without thinking.

I tend to always use remotes several yards, sometimes >10m from the car and in the past this has provided a good indication of a weaker battery because distance usage reduces before final failure.

s130 said:

I tend to always use remotes several yards, sometimes >10m from the car and in the past this has provided a good indication of a weaker battery because distance usage reduces before final failure.

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I replaced my two last night after reading your tale anyway.

Watch out for the rotating codes on the key. I don't know about this car, but my previous car would only allow 3 misses in a row (i.e. button pressed but car not receiving it), before it considered the codes to have gone too far out of sync. You then needed to open manually and go through some procedure to allow the car and the key to make friends again.

Same as my old VW. The Croma system is different, you don't have to synch the key to the car - I used my spare remote the other day and it worked straight away, I don't think the system uses rolling codes. No doubt some geek-type person will be along soon to elaborate further

I think the Croma does use rolling codes but I believe that modern rolling codes, taken from an initial seed value allow pseudo random sequences so many thousands (if not more) codes can be missed or skipped.

Theory - chose a random 64bit (or more value). This gives you a 1 in 1.8*10^19 (very very very large number - 180000000000000000000) chance of having the same number as anybody else. Now implement a random but known rolling code on top of that (eg. increment code by a count of 261 every operation). As far as the decode receiver is concerned in only needs to know if a remote code is in a 261 increment sequence from the known random seed value. Allow for wrap and job done. By the way a simple 'n' increment is so trivial to implement for modern systems that complex incrments based on other more complex algorithms are readily implemented.

I'm not a mathematician but the likelyhood of false code recognition is low. Even if there were other remote fobs that hit the 261 increment (or other more complex increment) sequence from the random base code, then all that gives is physical access to the car. As all modern cars then use RFID codes on top to free the ignition then the likely hood of getting all codes correct is, well, not worth worrying about.

The only reason remotes use rolling codes is because the code has to be transmitted and could be sniffed so this has to be protected against.

A physical key supported by unique RFID code that is only detectable with a few inches of the key secures the end game. i.e. vehicle abduction by driving away.

Sorry, not right - then you'd be able to use a sniffer to get in.

A good article:

http://auto.howstuffworks.com/remote-entry1.htm

They do use rolling codes but these days up to 255 misses are allowed. I guess there's little security risk in having a higher limit, as there are still only 256 codes out of over a trillion (40 bits) that will open the doors.

My previous car was VW group too. 3 misses was a bit mean.

According to Wikipedia, Fiat and VW both use the KeeLoq system.

Oh, and the receiver has a seperate memory for each key. You could use key 1 an infinite number of times and key 2 would still work.

Doofer said:

Oh, and the receiver has a seperate memory for each key. You could use key 1 an infinite number of times and key 2 would still work.

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Exactly as it should be becuase each key has to be registered.

Just reviewing your last link.

Doofer said:

Sorry, not right - then you'd be able to use a sniffer to get in.

A good article:

http://auto.howstuffworks.com/remote-entry1.htm

They do use rolling codes but these days up to 255 misses are allowed. I guess there's little security risk in having a higher limit, as there are still only 256 codes out of over a trillion (40 bits) that will open the doors.

My previous car was VW group too. 3 misses was a bit mean.

According to Wikipedia, Fiat and VW both use the KeeLoq system.

Click to expand...

Were you refering to my Post Doofer?

s130 said:

Were you refering to my Post Doofer?

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Yes, although I didn't intend it to sound as agressive as it reads!

It doesn't allow an infinite number of misses, as your post implies. Just a sensible number (255), not the 3 that VW used to allow.

Doofer said:

Yes, although I didn't intend it to sound as agressive as it reads!

It doesn't allow an infinite number of misses, as your post implies. Just a sensible number (255), not the 3 that VW used to allow.

Click to expand...

Wasn't aggressive at all. Just a little vague which confused me as to what you were refering to.

Ok. I can see why limiting to 255 is an advantage, especially when/for performance of locating a missing / skip code. Also limits the chances of encountering somebody else's code.