made from Sagem (French company... and I am french, hehe...), which came on many Scenic 1 phase 2, are really really bad. I got lucky and got mine with Denso
, they made more than 100000 kms, but only 40K for my father's Sagem ... The design is intrinscally bad as the
leaks current on the lower metal part which gets conductive. You can sometimes check with an ohmeter if they are good (connect one of top 2 connector and internal spring, then the other, you should have certain values, can be found easily on internet). But sometimes even
with good values are failed. Generally you changed all 4, but this is costly so you'd better change those actionned at the same time (cylinders 1-4 (external) and 2-3 (center)).
To check if they leak, you can plug one out and see if a spark is created between the lower part of the
and the engine block. In principle the current should only be driven internally, so if it goes outside anywhere else, your
I strongly recommend Denso or any brand with a similar design like Beru. Valeo also seems fine and cheaper. I do not recommend OEM replacement as you may end up with another Sagem... Going off
might just be a cheap replacement for 20K...
you can also replace the Torx bolts holding them by hex head bolts as the torx tend to get worn out. A set of 4 hex head size equivalent bolt with same diameter and pitch (metric obviously) should be cheap.