TIMM'S BMW E31
AND E38
IGNITION KEY
REPAIRS
E38 keys are pretty clever things. They
consist of three separate security devices.......the cut part of the key itself,
a radio frequency immobiliser and a transponder that is coded to the car. Since
I wrote this procedure it is now possible to buy replacement empty keys (no
transponder or remote), it is simple to swap the innards of a damaged key into
the new key and then get the shank cut at any key-cutters. Usual price around £8
for the key and £6 for cutting.
My main key was getting temperamental, sometimes it would work, sometimes not.
Although the battery was new, sometimes the LED would not flash. Time to take it
apart. No need for explanations to start with:
In the previous picture the transponder can be seen, here is a close-up of it:
It is a completely self-contained wireless transponder (Phillips PCF7930SA), it
is not wired to anything, is completely encapsulated and can be oiked out.
This bit appears to be the problem. This mylar film has conductive tracks that
rely on the graphite to complete the circuit:
A close look at the graphite next to the number '29' in the centre of the film
shows that there are two worn areas where the graphite has been lost. The key
body has two small pillars that push the film against the PCB. Here is the key
body and then the PCB where contact is made:
There's an easy fix for this one.....stick a little block of foam under the
mylar film:
The foam puts a little pressure on the film so that a new area of graphite makes
contact with the PCB.
Stuffed it all back together and all OK.
My other key was obviously a lot more worn and the 'Lock' button had collapsed
although it would still work if given a hefty squash. So I took that one apart
as well. The rubbery bit had distorted so it missed the right spot:
The rubbery bit is glued into the plastic to form a watertight seal and cannot
be replaced (easily). Buying a key from Ebay (£29) would involve trying to melt
the key shank off and installing the old one, possible and might be worth a go
in the future.
However, for now I'll reshape the rubber by poking a pen barrel around the
rubbery prong, straightening it up and then give it a good frazzling from the
outside with a small heat-gun:
A bit industrial and quite a bit of smoke but it did work when it cooled down in
the right position! Recently, I have seen the rubber parts for the E38 keys on
Ebay, this might be a more sensible option rather than frying them.
While it was apart I noticed it had the transponder missing! Although it works
the immobiliser and you can turn the ignition ON, it will not turn the engine
over......good thing I never relied on that then!
All done, time for a cup of tea......