Engine light on / alarm systems goes off

[robsm1th]

Hi looking for some help.

I have a 55 Z4 - owned it three years - very low mileage.

1. The engine light is permanently on. It's been taken to a bmw garage for an MOT (& passed) with only a warning that the catalyptic converter is on the way out but isn't a must fix yet. It's also been taken to a local garage who ran it through their diagnostic device and who found nothing to be wrong with it (not even the cat). Both garages re-set the electronics and light stayed out for a few weeks but comes back on again eventually.

2. Often (not every day - maybe every 3rd day or so) the car alarm goes off for no obvious reason. It's weirdly always about the same time of night (11.00 / 11.30 so luckily before bed time). An unlock of the door and a re-lock 'fixes' it temporarily.

I'm assuming the cat being faulty is something to do with the car alarm going off but I might be wrong (I know fjldkjflkj all about cars to be honest - I'm a petrol & water man when it comes to cars).

My questions are ......

1. why is the car alarm going off for no reason and

2. how the heck do I fix it when even garages seem unable to fix it for more than a few weeks?

A third question:

3. my old G reg Mazda MX5 didn't have a catalyptic converter thingy and it didn't seem to be a problem for the car (or me). Can the cat be bypassed to avoid having to buy a new one every five years or so?

The whole cat conv seems a backwards step to me but maybe the bmw have some sensible reason for installing it that isn't obvious?

[navid.v]

Hi Rob, you better post your issues in problems section of the forum, which you will most definitely get more responses.

I read somewhere on the forum the other day about the alarm and the issue was the bonnet sensor, do a quick search.

hopefully you get everything sorted

[robsm1th]

okey dokey I'll repost and also do a bit of a search.

[craig3.2]

2nd the bonnet catch, they can go faulty,causing "false alarms".
As for the Cat,it can be by-passed,with a cat-replacement pipe,but may then fail mot's,seeing as it will have a set emmissions limit which it wont meet??
Cats should last ALOT longer than just 5 years though. One of my old cars (which i owned new,for 4yrs) is still running around locally,with original cat,and its a 1998 Fiat Bravo