Transponder Key Probs

[slymiloni]

Hi all,

Previously had a problem on the wife's '97 Rav4 where one of the transponder keys stopped working over a year ago. Didn't do anything about it then as we had another key and the master key that both still worked. The spare key has stopped working now so I only have the master key. With the dud keys the ignition still comes on and the engine still turns over but just won't fire. I think the imobiliser is cutting the fuel and not the spark as if the engine has only just stopped, it will fire with a dud key but only for a second, tell me if you think I'm wrong there.

Toyota want £22+vat for each new key and £35+vat to reprogram them. There's a local guy who specialises in this kind of thing who may be able to do it a little bit cheaper but will the problem come back again? Do these transponder keys just have a finite life, they've lasted 13 and 14 years, how long will the master key lasr? The keys don't have a Battery as far as I can see so how does the transponder transpond? If it's totally electonic with no moving parts, what goes wrong? I'm convinced it is the keys because I only have to hold the master key next to the ignition to make the duds work. Does the immobiliser register the keys or are they themselves programmed to the immobiliser code? Has anyone simply reprogrammed the keys succesfully or would new keys be in order?

The big question is would it be easier to just rip it out?!?!? I've seen several posts by Bothwell Buyer (are you out there?!) about removing alarm/immobiliser systems but was wondering if on this model the immobiliser and alarm/central locking are independant systems or are they linked? I have seperate fobs which operate the locks and alarms and these both work as advertised, it doesn't matter which one unlocks the car to affect the starting problem. I see it only takes a couple of hours to remove the whole lot but don't really want to lose the blippy unlocking side of things. Has anyone removed just the key transponder side of the immobiliser and left the alarm and remote central locking in place?

Cheers in advance...

[bothwell_buyer]

Morning. There was a post on here just a few weeks ago about someone who had a car stuck in Europe (I think) with much the same problem about the transponder but they didn't have the master.

Yours sounds like the slightly later version of the alarm system - ie the early ones that had the transponder thingy in the key. I have a Previa 1997 that seems to have a similar system. I got spare keys cut at Timpsons and they fixed the transponder thing...seem to have a wee gadget for it. I guess its a bit like the tags you get in shops that set off an alarm if taken thru the doors. From memory, which is becoming poorer, the keys for the Previa were maybe around..... naw...can't remember but it was more than a normal key. I'd guess less than £35 but. Defo get a couple of spares done while you still have the master.

I think its a bit more work to remove the immobiliser system, but as we all know, there are experts out there who manage it when nicking the car !!

[shcm]

The keys don't have a battery as far as I can see so how does the transponder transpond?

There is a usually coil around the ignition switch barrel. The coil is energised @ 125kHz. There is a corresponding 125KHz circuit in the key, which picks up the 125kHz field generated by the coil, rectifies it to DC, which provides power for the transponder electronics. I suppose it could be considered a bit like a transformer, or similar to the way a cordless tooth brush is charged.

The car side of things also modulates the field generated by ignition switch barrel coil, which is how it communicates with the key. It's Amplitude modulation if you like. The transponder talks back by "disturbing" (it changes the effective transformer impedance of the coil) the 125kHz field generated from the coil. The "disturbance" is very small, but can be detected by the car. The fact that is small is one of the reasons why it's quite difficult (but not impossible) to eavesdrop on the communication.

Well you did ask!!!!!!!!! :).

If it's totally electonic with no moving parts, what goes wrong?

The transponder contains "Esquared" (EEPROM) memory. A bit like Flash memory - which most people have heard of (i.e. USB memory sticks). Both Flash and EEPROM memory do eventually "wear out". EEPROM is guaranteed for something between 100,000 and 1,000,000 write cycles (I've seen transponders spec'ed to 100,000). Depending on how the security is implemented, the EEPROM in the transponder, could be being written to every ignition cycle.

I'm convinced it is the keys because I only have to hold the master key next to the ignition to make the duds work.

?? Are you sure it is not just talking to the transponder in the master key? i.e. the duds are still dud and the transponder in the master is actually doing the mobilisation?

Does the immobiliser register the keys or are they themselves programmed to the immobiliser code? Has anyone simply reprogrammed the keys succesfully or would new keys be in order?

Each transponder usually has a unique ID, which the immob electronics has to learn and store. For most systems the procedure is something like - the system is put into programming mode with a master key (which the immob already knows the unique ID for) to prove you have the right to add new keys. Then the new transponder is presented so the immob can learn its ID.

[bothwell_buyer]

don't you just love a know-it-all ???

[headhurts]

Phew!

Fair wore me out reading this, the price being quoted by dealership seems reasonable to me and you would know (hopefully) a proper job will be done.

Try talking to Jag dealership re keys and programming it's eye watering.

[slymiloni]

I think that's just about covered everything then?!?! That's cool though, it's told me what I want to know, probably not worth trying to recode the old transponders. Going to Toyota tomorrow to get new keys sorted, guy with van that does them locally was pricier would you believe?

But then, does that mean the master key only has a finite life as well then? Should I not be using that day to day as I have been? I know you can still get new keys done so long as you have one working but it's apparently easier and cheaper if you have the master.

Cheers, will let you know when it's all sorted...

[slymiloni]

Oh dear, it's all gone wrong! What I thought was the working master key as it has the key cutting code attached to it is actually the grey valet key and is only a sub. The two black keys that don't work were the masters. So I should have got something done when one of these masters failed last year.

So Toyota guy informed me that you can't recode new keys from a sub key and I will have to have a new transponder computer + new keys + coding + labour all for £359.02!

So, I'm gonna have a coffee then rip the immobiliser out...

Wish me luck!

[slymiloni]

Update, I've ripped the car to pieces and have found that the immobiliser seems to be factory fitted hardwired in so there's no obvious joins or splices that could be unspliced to simply remove it. The alarm unit seems to be a seperate bolted on unit but that's not the problem.

If I take the immobiliser ECU out once the engine is running then it carries on running so I deduce that it must only send an enabling signal to the engine ECU to get it started. Could this be as simple as earthing/living a pin on the engine ECU. Anyone got a pinout for one of these engine ECUs? It'sa 89661-42190 3SFE.

The case continues.

[slymiloni]

Leaving it there for tonight with all but 3 of the immobiliser wires accounted for which all go off into the engine bay. Still can't find a link to the engine ECU, could really do with a wiring diagram now but all the ones I found online seem to be for later years. Mine's a '97 but is a Spax special edition so may have the next year's kit fitted.

I'm left with a green/red which is constant 12v out from immobiliser ECU, a green/yellow which seems to pulse 12v for half a second every second and a blue/white which doesn't seem to do anything, perhaps an output to the immobiliser ECU.

All is not lost as I can always tape the remaining subkey inside the steering column near the sensor ring and use the other two keys to my heart's content although this is not permanent as the key could also die putting me back to square one. Ideally I'd just like the immobiliser gone/bypassed permanently. Any ideas before I get back on it tomorrow? Any budding car thieves out there wanna point me in the right direction and do something good in your life?!

[bothwell_buyer]

Given my physical infirmity and lack of patience and escalating intolerance, I'd hit the car with a branch from abirch tree....I can supply them free of charge ... and consult my local friendly garage. Any garage specialising in Jap cars should be able to help you out. Dunno where you stay so can't recommend any but there are loads about - maybe on ethat imports Jap cars ????

Its not rocket science as the design will be older than schm's age I'm sure.

Some owners of modded Jap cars get a specialist to change the alarm and immobiliser system to kick in after the car has travelled a short distance if stolen...so the thieves just abandon it rather than trash it.. so these things can be done.

[slymiloni]

What's your shipping rate on that birch branch?!?!How on earth do spotty hoody teenagers manage to drive these away without permission?!?!

Spoke to a local auto-key specialist who sounds confident that if any of my keys work then he should be able to reprogram the ECU and all the keys for £120 which he won't charge me if it doesn't work but he does sound confident. If the keys are dud then carkeyhelp on t'internet will supply two cut and ready for programming for £35. If I just use the grey valet key it will cost me nothing but loss of pride and feeling of being beaten by technolgy (albeit 14 year old technology!) It appears it actually is comparable to rocket science!?

Going away with work until end of July so I'll leave it until at least then and see how flush or interested I feel on my return.

I did discover accidentally that your Battery must have a really good charge for the immobiliser to work. After testing this key then that key repeatedly they all packed up despite the engine turning over nicely. A quick recharge with the Battery disconnected did the job, for the grey valet key at least. Just one for you to try before ripping all your wiring out!

[zimboy]

Hi All, i've just had a similar problem, our Rav4 keys apear to have been dropped one to many times (considering i've been banished to the motorbike i've been make to take collective responsibility anyway, the plastic part that holes the imobiliser buttons has split around the screw thus not really holding the fob in any more. Thinking i'd be clever i jumped on eBay and then spotted "flip out key" blank. i tried to drive the car today with the fob in the new key holder (but i haven't had it cut yet) used the orignal key without the fob and it doesn't start, so do i bother getting the key cut will it work? (i had to resort to the spare without the fob (this works)

thanks

[junebug1701]

Hi All, i've just had a similar problem, our Rav4 keys apear to have been dropped one to many times (considering i've been banished to the motorbike i've been make to take collective responsibility anyway, the plastic part that holes the imobiliser buttons has split around the screw thus not really holding the fob in any more. Thinking i'd be clever i jumped on ebay and then spotted "flip out key" blank. i tried to drive the car today with the fob in the new key holder (but i haven't had it cut yet) used the orignal key without the fob and it doesn't start, so do i bother getting the key cut will it work? (i had to resort to the spare without the fob (this works)

thanks

You need to transfer the immobilizer chip from the original key to the flip key. The chip is a tiny thing that looks like a bit of black plastic glued into a slot. It has nothing to do with the buttons or the remote fob transmitter.

[zimboy]

Hi Junebug,

thanks for the info, at least now i sort of know what i'm looking at, tiny problem... i used the old key to try start the engine, with out the fob, and it didn't work. i have had look inside the old key but there isn't a chip there. i know the keys were dropped outside, how strongly glued in is that imobilizer chip? it looks quite tiny so the chances of locating it outside (on a gravel driveway) looks slim?

no idea if it makes any difference but i have the two button remote (i assume the all work the same)

thanks again

[zimboy]

Right, i popped the fob back in the broken set of keys and it works, but doesn't work without the fob?

[junebug1701]

Right, i popped the fob back in the broken set of keys and it works, but doesn't work without the fob?

Well, that's strange. Makes me think the chip is in the fob. But if that were the case, you would think the fob in the flip key would work as well. Unless the chip is too far away from the transponder ring surrounding the ignition. Examine the fob transmitter and see if the chip isn't there. Oh, and the chips are glued very well in my keys--no way could they fall out.

[zimboy]

Hi Junebug,

thanks for the advice i will see if there is anything i can do to make a plan, not sure what yet :) but there has to be a way, it's better than being told a new key will cost £150.00 to cut with a new chip in it. (local locksmith wont' cut keys' they don't supply)