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Pete, Mercedes Mechanic
Category: Mercedes
Satisfied Customers: 28815
Experience:  Over 15 years experience as a Mercedes dealer technician
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I have a U.S. Spec 2000 Mercedes C230 Kompressor Sedan

Customer Question

I have a U.S. Spec 2000 Mercedes C230 Kompressor Sedan (W202) chassis, the last 8 of the VIN are: YA814496. My problem has to do with the siren for the factory alarm system: About 6-8 weeks ago I noticed a bizarre noise coming from the front of my car
(when the car was off). It would sound like a rapid chirping. Upon doing some closer inspections I found that the noise was coming from my original alarm siren - so I disconnected it with the intention of replacing it when I got the funds to purchase a new
one. I finally purchased a brand new siren from the local M-B dealer about a week ago and installed it today. I tested it by locking the car and then pressing and holding the "Panic" button on the key fob. The hazard lights flashed (as they normally would
and should) but yet I still get no sound from the new siren. Could this be a fuse or relay issue? I am hoping that the alarm module isn't bad as it will be cost-prohibitive to replace. Thanks, ***** *****
Submitted: 2 years ago.
Category: Mercedes
Expert:  Pete replied 2 years ago.

Hi my name is ***** ***** I will be happy to assist with this today.

Check and make sure fuse 7 (5 amp) in the trunk fuse panel is o.k. as this powers the alarm siren.If this fuse is o.k. and with what was occuring before the horn was replaced this sounds like a fault with the PSE control module itself internally as this controls the alarm siren itself.I have seen this fail before requiring replacement.

Thanks Pete

Customer: replied 2 years ago.
I went through ALL the fuses - several times - in both the front fuse box as well as the one in the trunk. I took a particularly close look at fuses 2,4 & 7 in the trunk fuse box as they are, according to the label inside the fuse box cover, the ones responsible for the alarm system. All 3 fuses are fine and intact.So am I understanding you correctly in that you're suggesting a complete replacement of the PSE module? If so, is there any way I can test it before replacing it? Is this a costly part? Is this something I can do myself (I am VERY mechanical and am doing my own brakes today, in between these communications)?Please advise re my above 3 questions.Thanks,
Expert:  Pete replied 2 years ago.

Hi Mark.

My info isn't showing how this is tested.Usually this is tested electronically with a dealers sds machine as it walks the technician through the diagosis for the alarm horn fault.The new PSE has to be coded to the vehicle using a dealers SDS machine after it is installed.In the link below you will see the location of it on your model here.Coding can generally take around a half hour to an hour to do in some cases.

Thanks Pete

Customer: replied 2 years ago.
Thanks for the info Pete as to where to find the PSE. I am going to check it tomorrow or one day this week to see if there is any evidence of corrosion around the contacts for the wired connectors.One last idea... I've been reading on the internet and it was suggested that the earth (brown wire) be tested. I see there are 3 contacts on the connector to the siren. One wire is brown - so I assume this is ground. I am not sure what the other 2 are for - is there some way I can test at the connector to determine if the ground is the problem or whether it's just a positive signal that the siren isn't receiving. I'd really like to try and troubleshoot this myself as I know bringing this to the dealer is going to cost me way more than I want to spend.Any last advice regarding possible testing procedures at the connector for the siren?Thanks,
Expert:  Pete replied 2 years ago.
Your welcome.I apologize for the delay.
Looking at the diagram info on this model here the brown wire is the ground that connects to a ground point on the body as well as ties into the engine hood alarm switch.The red wire with yellow strips is the power feed wire to the horn from the fuse listed above.The yellow wire with red stripe is the signal wire from the PSE to trigger the horn to go off.
Thanks Pete