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Peugeot 206 car key replacement error highlighted using SDRPlay

My car key was falling to bits. The unlock button had long since given up on the remote control. Things were getting a little bit inconvenient!

Time to go and get a new key.

A quick trip to Timpsons informed me that the key would have to be taken to a main dealer as they couldn’t copy them them due to a transponder inside the key fob that had to be matched to my car. Of course there’s always the electronics for the car as well that needs to matched, otherwise anyone could break into any car! A little annoyed I went off to the local Peugeot dealer and asked for a price. After being told that a replacement key would be £80…… VAT, I exited the reception before I was in need of a qualified first aider to perform the Heimlich manoeuvre on me.

A quick internet search revealed that the Newmarket Tesco had a key cutting stand in it that specialised in car keys….but even then I was quoted £64 inc VAT. Surely it couldn’t be that much. Just open up the case and transfer bits to a new empty case…surely? Ebay to the rescue seemed to think is was possible with key blanks being sold for under a tenner. I ordered one.

2 days later it arrived. I swapped out the electronics and the blade into the new case and voilà…. it didn’t work! Engine turned over and it refused to start. Typical immobiliser type of problem. What was going wrong?

The car unlocked correctly with the ‘plipper’ operating at 433MHz. Using the SDRPlay receiver, I could clearly see the signals being sent. No problems here. In fact 1 press of the button results in the unlock code being sent multiple (normally 2 or 3 times). The engineer in me realised that this was probably a trade off between battery life for the ‘plipper’, and reliable unlocking of the car. Of course I still haven’t worked out why people press buttons harder when they know that the battery is weak or flat? Do you do that?

Next I knew that the key was energised by a coil in the ignition at 125MHz, which was easily detected.

The response at 315MHz from the key was missing. A quick check of the old fob revealed that there was a separate ID 46 transponder chip in the key. This was pretty much the same colour as the plastic that encloses it and looks almost as if it is part of the key fob. Swapping it over resolved the problem and my car burst into life once more.

Radio frequency visualisation with the SDRPlay

I was given the opportunity to play with the SDRPlay software radio. Radio frequency visualisation is traditionally impossible to do without expensive equipment and a fair amount of technical knowledge. As a result ut’s one of those areas that normally when faultfinding we rarely have direct visibility of.

I’d just been given a ‘dead’ remote controlled car. Dusted down car, changed batteries and nothing.

……so today was the day to try out the software radio. A quick check of the controller showed that the transmission frequency was 17MHz.

Installation of SDR Sharp was reasonably easy, and a quick check at 17MHz showed that the controller was transmitting something. This gave a good indication that the fault was likely to be at the car side of the radio bridge. A little disassembly showed no power to the motor that was traced back to a broken solder joint at the battery holder.

This is just one example of how the SDRPlay software radio can help simplify the fault finding process by providing an additional cost effective tool that helps to speed up location of a fault.

We now use the SDRPlay software radio for helping children to visualise what is being transmitted when building a 868MHz radio link using RPis and a USB  radio serial link.