WFS Transponder: Troubleshooting Age-Related Issues

Hello,

Take a look at this:

http://www.motor-talk.de/t168537/f146/s/thread.html

Is there any truth to the information provided by Bosch that key transponders weaken over the years and need to be reprogrammed, or is it just nonsense?

If that's the case, then why did a re-encoding help?
According to my understanding, the STG (Steuergerät - control unit) is only told "If a key sends this or that code, it is authorized to start." And the key draws the energy to send the signal from the magnetic field of the reading coil just before that moment... or am I mistaken about the basic function of transponders }? (If so, please explain it to me!)

I don't want to deny that the transponder in the key is aging.
The signal could actually become weaker due to mechanical aging.

The thread's factual competence can be seen in the statement '...Magnet [...] This induces a voltage in the small reading coil.'

If the WFS is malfunctioning, I would also recommend having the keys reprogrammed first; 'coding' is, in my opinion, the wrong term. It sounds like the transponder is being coded to release the WFS, which isn't the case.

Okay, okay...

I have found the glass tube transponders to be exceptionally robust.
They are almost impossible to kill. Especially not in the key, it's far too well-padded .

It's possible that solder joints could crack due to thermal stress over time. However, this is relatively rare and, with good manufacturing, should take a very, very long time.

You've correctly identified the principle of operation. The reading coil induces a voltage in the transponder, which it stores in a capacitor. After the induction is switched off, this voltage is sufficient for the transponder to send its code, which the reading coil then receives. This process is repeated a few times.
We had something similar as a final exam .

CU Gremlin.

Hello,

Quote:

I have come to know the glass tube transponders as being extremely robust. They are almost impossible to kill.

"I feel the same way. During my test series while I was studying, that was the only constant."

Hello again,

Thank you for your answers.

I'm trying to imagine what might be behind the story from the link, if it's true.

So, if the transponder itself isn't aging, but still needs to be reprogrammed, then something else must have changed.

*Speculation mode ON*

For example, the WFS module connector to the reading head corrodes over time.

Episode 1: Due to a reduced current flow in the coil, the transponder receives less "transmit power."

Episode 2: The WFS receives the signal again, but even weaker this time, causing the response code to be read incorrectly at some point -> a re-initialization is necessary.

*Speculation mode OFF*

Would that fall within the realm of possible explanations?

certainly...

The reading head has appeared in workshop documents on several occasions .

Sure, here is the translation of the text from German to English:

'Cu Gremlin'

Hi,
The component most likely to be affected by aging is the storage capacitor.
in the transponder. If it weakens, this can affect the transmission power and the...
Affects transmission duration.
If contact problems then arise in the receiving coil, it can eventually lead to these issues.


Best regards, Rudi.

Rudi wrote:

Hi, The component most likely to be affected by aging is the storage capacitor. in the transponder. If it weakens, this can affect the transmission power and the... Affects the transmission duration.

Hi Rudi,

Do you happen to know if the capacitors that are prone to drying out are µ-Elko or film capacitors?
(Just out of curiosity, I definitely won't be replacing those things in the transponder ).

Hi Ulf,

Unfortunately, I don't know.

Since all the electronics are encased in a glass tube approximately 1 cm long.
(with an outer diameter of just under 2mm) and occupying most of the space for the antenna.
If a lot of space is used for other components, there isn't much room left for the capacitor.
If you also consider the relatively small number of charge/discharge cycles, then...
Could a transponder also be considered very reliable if it uses an electrolytic capacitor?
(especially if it's tucked into the folds of a dachshund's back or in the pocket of a pair of pants).
A car driver endures their existence in temperatures of 20-30°C.


Best regards, Rudi.