203 Alarm

[david b]

C-Class 203,
On returning to the car I sometimes find the indicators flashing as if the alarm has been triggered, this tends to happen once or twice a week for no apparent reason, and ideas?

 

[Nibbo]

Usually indicates that a motion sensor has been triggered. This can often just be a spider.

 

[ROBB]

could be the alarm siren back up battery on its way out. if it is - the silent flashing should start sooner and sooner after you lock the car

 

[david b]

Still same problem indicators flashing on return to car about twice a day now, any ideas please?

 

[Shude]

Try turning off the internal motion sensors (there is usually a button for this on the dash). If this fixes the problem then there is likely something crawling or flying around in your car while you're not in it, causing the alarm to go off.

Mine did this for ages a few years ago, the stupid spider used to make webs OVER the sensor on the door pillar!

 

[david b]

Tried it last night the indicators flash but siren doesn't sound,
when I press locking button on fob it flashs 3 times to set it then if I press locking button again it flashs indicators like a strobe light.
Q: should siren sound when triggered?
Q: where is alarm control unit located?
Q: where is siren located?
Q: is there a separate fuse for the siren?
Any help please.

 

[david b]

Would a faulty siren trigger the alarm?
Has anyone taken the siren off and dried it out and did it work?

 

[AndyPCD]

Yeah a faulty alarm siren would cause the alarm to go off as it thinks the voltage has been diconnected.
There is no point trying to dry out the siren as the water ingress damages the internals.
If you replace the siren i would check the wiring as this can corrode as well and will need replacing as well

 

[david b]

Can't find where siren is located any ideas anyone?

 

[alexander patie]

n/s (possibly o/s) wheel arch at the back/bottom behind a plastic panel.

as above it will be your trouble - the fact that it does not work is the clue...............

 

[david b]

Would the car run with siren disconnected?
Is it easy to change the siren?
Has anyone replaced the siren with a different one?

 

[ROBB]

n/s wheel arch at the back/bottom behind a plastic panel.

as above it will be your trouble - the fact that it does not work is the clue...............

under n/s wheel arch. have to remove fair amount of pannelling to get to it. Yes the car will run with it removed. problem is not moisture but built in backup battery. as backup battery fails - alarm is triggered (silently).

once panneling is removed - 1 TX30 (i think) is all that is holding it on.

you will need to have the codes reset via star once it is replaced. mine was approx £80 - but these are common across lots of models.

 

[david b]

It's not just a case of removing the old one and replacing it then?

 

[BlackC55]

No, the wiring tto the siren often corrodes too and mor often than not the plug connector has to be replaced too.

 

[ROBB]

No, the wiring tto the siren often corrodes too and mor often than not the plug connector has to be replaced too.

i must have got lucky

should be simple to r/r a connector though (cut/splice new?)

 

[BlackC55]

The pins have to be removed with a special tool and then new pins crimped and soldered. Fiddly little job too.

 

[ROBB]

The pins have to be removed with a special tool and then new pins crimped and soldered. Fiddly little job too.

But aside from that (might not happen) it is a fairly simple DIY job

 

[BlackC55]

yes

 

[david b]

Sorry didn't understand why I would need to have it recoded if I just swapped the siren?
Would it be most likley that the siren would cause the problem of indicators flashing with no sound from the siren?

 

[ROBB]

due to the ecu detecting low/no voltage from the alarm siren backup battery (on account of it being knackered ) a fault has been triggered in the ecu - which manifests itself as silent flashing. once the siren is replaced - STAR is required to clear the ecu of all stored faults. as the siren fault will not exist after changing it - the ecu will ot keep triggering the flashing.

further to that i cannot explain; why is grass green?? why do women know everything??

thats just the way it is