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Before starting to describe the problem, I need to say that this is my first time posting on electronics.stackexchange. I don't have a deep knowledge of electronics but I usually can diagnose a problem. I work as a software developer for a company that works a lot with electronics, so my limited knowledge comes from that.

That issue that I bring you today is more of a personal one. I bought a used vehicle a couple of months ago (Peugeot 207) which came with two keys.

  • One key without remote control (only opens doors by using the lock). The only electronic aspect of this key is that it has the immobilizer needed to start the car.
  • One key with remote control (the original key from manufacture).

Right after buying the car, I noticed the problem. The remote control wasn't working. Nothing would happen whenever I clicked the buttons. It was only some days of persisting with methods of "synchronizing the key" that I found that the remote control was actually working, but only when right next to the steering wheel. I quickly found that the receiving module of the car is located on the steering wheel, so it made sense, the remote control was working but with an extremely low signal.

After searching the topic for some time online, most people with identical problems found it to be an issue with the battery contacts or the battery itself. At this point, I had already changed the battery to a new one, but for the sake of being sure, I changed again. I changed batteries twice with trusted brands and I even tried using a power supply directly connected to the contacts. Nothing different happen, the remote control would still work only next to the steering wheel.

At this point, I gave up for some days, I was wasting too much time on this issue and I was having no progress. When I decided to try again, I found that the remote control was not working at all now. Not even next to the steering wheel. I thought that maybe I had to synchronize the key again but that didn't work either.

This made me even more persistent in finding the source of this problem. I was yet to understand if this issue was from the key or from the vehicle module. I have no other key with remote control to compare with. Luckily, I work in a place with a lot of electronic testing devices. So I decided to use them to diagnose this problem.

I started with the basic, is the PCB even reacting to the button presses? I used a multimeter to compare the consumption whenever I clicked a button. It was pretty obvious that it was working. When I click a button the consumption peaks at 11mA.

Great, that is good. But now the real test. I have the luck to have an RF analyzer at my work, this is the best I could have asked for. So, I configure it to 433Mhz and place the key inside the chamber while I press the buttons. That when I noticed, no RF is being transmitted at all. None that can be detected. I compared it with a key from a colleague and it was pretty obvious that the machine was working correctly.

So, this is what I have, a key with remote control that in every way seems to be working, but not transmitting any RF signal. I thought to myself, it is probably the antenna, but where is the antenna (I am not great at electronics sorry). From online sources, everyone refers that the brown component (left top corner) is the antenna coil. But from what I found, that is the antenna for the immobilizer. The immobilizer is working great, so I don't think that will solve my issue.

I can't find anything online that tells which component can I try to replace. What are your thoughts on this? Any professional opinion is welcome.

PCB identical to the one I have

Thanks for your time!

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    \$\begingroup\$ antenna is the topmost component in the picture, the black block with the copper colored rectangle ... i had an issue with my fob when one end of the antenna detached due to fob being dropped ... pressing the antenna against the PCB pad made it work ... you may have a detached antenna or a broken PCB trace \$\endgroup\$
    – jsotola
    Commented Mar 9, 2021 at 20:20
  • \$\begingroup\$ The ferrite rod is a precision L inductive antenna. Call the dealer and ask 1st. We have had a rash of weekly neighbourhood car thefts because technology exists to sniff RFID tags and clone them because they broadcast too far. But yours has a button which helps security for the interrupter under the hood. Check the frequency stability against spec in PPM error and how much that changes with hands around case. Something may have also drifted off a very narrow band. or it works differently by Rx before Tx. Use a long wire into SA for Antenna if necessary. Then find how it is supposed to work. \$\endgroup\$ Commented Mar 9, 2021 at 20:29
  • \$\begingroup\$ That means you need to borrow the SA and see if your steering wheel is pulsing bursts of RF. Or use a portable EMI field meter. If battery Voltage doesn’t change more than 5% when button is pressed, it’s OK. weak batteries have higher ESR. \$\endgroup\$ Commented Mar 9, 2021 at 20:31
  • \$\begingroup\$ Can you post a bottom side of the pcb as well? \$\endgroup\$ Commented Mar 9, 2021 at 22:16
  • \$\begingroup\$ The picture quality isn't great, but the solder joints on the black component to the right may be questionable. I suspect that this is a ceramic resonator used for the radio, but I'm just guessing really. If my guess is correct, you will be able to put an oscilloscope probe on either pad of that component, turn the time ref down to nanoseconds and you should be seeing a sine wave. If you don't see anything there on one board but a sine wave on the other board, then that's the problem. In case the oscillator is missing, then the radio won't function at all. \$\endgroup\$
    – Lundin
    Commented Mar 24, 2021 at 9:59

1 Answer 1

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I am thinking it might be the coil. If the coil works fine, using the multimeter, measure its resistance on its two 'legs'/points. It should be something like 1 ohm, 3 ohms, 5 max. (Measure the resistance with the battery disconnected or you might damage your multimeter)

Check some videos with people repairing wireless car keys online, it might help:

https://www.youtube.com/watch?v=RRtFrShU-mk

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