W163 desperate alarm problem

[allias]

Hello

I recently swapped my beloved W210 V reg 320CDI on to W163 X reg 320 petrol and few problems started.

First and most annoying and loud is my alarm siren that goes on only at night time - yes only at night time. My neighborhoods are really delighted. After suggestions I decided to swap siren which was located behind wiper motor assembly and guess what - first night and it goes off again. WTF???

I tested battery as I thought it would be a voltage drop but it seems to be steady 12.3V.

What else? What part will react to day light or temperature and could effect it? How come this still goes on and on? Heeeelllllppppppp....!

 

[allias]

Tested for bonnet sensor and it seems to be fine with no circuit issues.

What else?

 

[Dec]

Did you do an autopsy on the old alarm siren to determine if it could have been causing the fault?
The replacement siren, was it new or used?
When you lock the car with the remote, do the hazards flash 2 times or 3 times?
You could try turning off the internal motion sensors every time you lock the car to see if that makes any difference.

You could, if possible, put the car battery on a trickle charger well before you expect the next false alarm to see if that makes any difference.

Dec

 

[allias]

1. Siren is brand new from dealer (I only go for MB parts)
2. How is it makeing difference if it is 2 or 3 flashes while locking with remote?
3. I tried with internal sensor few times and it doesn't seems to make any differences.
4. I tried to eliminate battery as I had once charged overnight and that did not make any difference. 12.4V and above. Tested at time if goes off and never goes below that. Is there a limit it triggers alarm? Is it worth changing battery all togheter?

I know it might sound stupid but it seems to me as it might be under influence of temperature. I tried yesterday (about 7PM) with diconnected temperature sensor (seems to be on same circut on diagram) but it didn't go of untill 10PM. As a result I had to disconnect battery again to not wake-up neighbors at night. This morning I connected battery (left sensor diconnected) and left for work. My wife called me 2 min later saying if goes off again and she can't stop it.
I came back and tried to do the same to exierience it - no luck. I was soooooo hoping it would be related to temp sensor. I got one from work today so I will see if new sensor will make any difference.

While I did checks yesterday I looked on bonnet switch and found it very oily. Someone had it treaded with WD40 before. I cleaned and I tested switch and circut with multimeter to eliminate that as well.

Im running out of ideas. I really dont want to keep siren disconnected due to area I live. I really dont fancy spending X amount of £££ for diagnosis which will tell me I need control unit above my mirror. (which I wont change anyway)

It must be something really stupid.

 

[Dec]

If a door /boot/bonnet is open (or the car thinks something is open because a door pin is not working properly)when the car is locked with the remote then the hazards should flash 2 times instead of 3 times.
Try it by locking the car while a door is open… the alarm wont go off but you should only get 2 flashes of the hazards instead of 3.

A sudden drop in voltage should trigger the alarm, for example, if someone disconnected the alarm siren or the car battery WHILE THE ALARM IS ARMED i.e. when the car is locked the alarm is armed.
Do you have any idea how old the battery is, if there is no obvious build date markings on the battery then the only way of knowing how old it is, is by looking at the underside of the battery for a moulded build date like the one in picture below.

See… Build Date

I cant see how light or temperature would have any effect on the problem , my money would be on a battery fault of some kind, I believe it does need a sudden voltage drop before the alarm would trigger.

Dec

 

[allias]

Dec


Thanks a lot for your input. I will check all of it again. For some reason battery seems to be my biggest suspect despite being tested alright. I might have a go and "borrow" battery to see if any better.


My current battery is obsolete superseded part number so I know it is not the newest one (even when it seems to be OK) - don't know the date but I will verify that as well.

 

[frog1520]

You could always leave the alarm off at night, so you can get some sleep!

With the drivers door open, lock the doors with the central switch from inside the car and then close the drivers door and lock it with the key blade....

 

[allias]

I have done this for times when I wanted some peaceful sleep. But that's not the point.

I have changed battery for brand new and alarm went off again. But at the same time a friend mentioned about sync'ing keys. Interesting thing I did sync on one of the keys over week ago. Same time when problems started. Coincidence? I did sync on both keys again to make sue they work fine. I was having alarm going off every 2-3 minutes. I wonder if it is related to keys??

While I was doing sync I looked at the back of vehicle and found something what I haven't notice before. It looked like black speaker size ~3/4 inch with + & - on it and wire going behind trim. Is it located behind seats near top trim on passenger side. I wonder if this is some kind of EDW alarm sensor? If it would be loose, it could trigger alarm as well with just small wind moving vehicle of if it is microphone it could react to noise...??? Anyone seen this before? - sorry cant get picture of it

 

[Dec]

Locking the car with he remote arms the alarm, hazards flash 3 times.
Unlocking the car with he remote disarms arms the alarm, hazards flash 1 time

Is the above what you are getting when locking/unlocking?

That “speaker” may be a motion or glass breakage sensor, the + and – may be for adjusting the sensitivity of the sensor.
There may be a hole to insert a very small screwdriver to adjust the sensitivity of the sensor, + to increase and – to lower the sensitivity… the hole may be concealed behind a rubber blanking bung.
Like the second picture here… Bert Rowe's-A-class info. Information A160/Feb 2002 Scorpion Car Alarm System.

Dec

 

[allias]

Dec: Mine does exactly as you described.

My "speaker" was all round but yes - same concept.

I got a feeling that "speaker" was causing my alarm to go off. I was hanging loose so it could be picking disruptions and triggering alarm. I hidden it behind one of the plastic trims. So far so good and no siren since morning but tonight after 11PM will be my moment of truth.

 

[Dec]

Is the car parked on a public road? Could someone be shoving the car on purpose so as to trigger the alarm, it’s very odd that it’s a night time only event.

Dec

 

[allias]

No it is on driveway and I thought about it but no influence of 3rd party people. Checked on CCTV to confirm.

I got theory which I will mention when I will know fix - I think Im getting closer. If it is correct it will either be quiet all night or should go off about 6-7AM tomorrow morning.

Will see.

 

[allias]

I was about to celebrate this morning as it was first night since previous Friday to have no alarm at night. Unfortunately is went off again about 2 hours ago. It was in very windy time so it is hard to tell if it was due to my fault or harder wind shake of my car.

Firsly I need to mentioned what I have done yesterday. I disconnected one key remotes (battery off the one I had it off when I bought the car) and re-synced other key which we used since first day.

I got a feeling it all must be linked to either keys or it must be knocked sensor Im not aware off. Does alarm system comes with shake sensor or something in this kind?

 

[Dec]

Towaway sensor and glass breakage sensor, page 36 here… http://www.mbusa.com/vcm/MB/DigitalAssets/pdfmb/ownersmanual/2001_ml320_ml430_ml55.pdf

Also… http://www.mbclub.co.uk/forums/electronics/66904-interior-monitoring.html


Dec

 

[Dec]

I wonder if the below has anything to do with your problem, haven’t got time to read it all.

See… Permanently disable tow/tilt sensor. - Mercedes-Benz Forum

and link in post #4… Retrofitted Trip Computer into ML 320 2001.. I have 9 fingers now.... - Mercedes-Benz Forum

Dec

 

[allias]

Thank Dec for all the input. It looks as I lost the battle. I will be disconnecting siren - at least for now. At the moment I use key to lock vehicle and remote to open and that keeps alarm dis-armed.

 

[Dec]

Sorry there was no solution, let us know if you ever get to the bottom of the problem.

Dec

 

[allias]

Weird...

Sunday siren went off and I told my wife (main driver) to lock with key blade to keep alarm disarmed. Yesterday I was planning to take job again to disconnect siren and right before I was about to do job we got to talk and she is like:
"...yes I have been locking by key... you know by remote with button..."

I was like

And since Sunday she was locking "by key" and me thinking - great it is quiet when it actually turns out it is fine now.
Great time for me to know I don't have to disconnect siren and wake up in a middle of a night to disconnect battery.

Bad thing - I got no idea what was the actual fix, but I figured I will create summary so someone else could use it.

1. Siren - it turns out to be fine.
2. Battery voltage was 12.35V with engine off and tested OK with Midtronics tester but I decided to change to new one and it is 12.85V at the moment. Did battery made that difference? I don't know.
3. I do have piece of "brown tape" over inside sensor but I seriously doubt it would make "such impact".
4. Key synchronization. I left one key disconnected with 2 batteries out. I Re-sync'ed other key. Somehow I got a feeling my other key is making it to go off due to fault on syncing - again don't know for sure.

When I got spare minute and I will be missing sound of ML siren I will do few tests to see if I can find fault as I can't believe it got fixed by it self.

 

[Dec]

It might be wise to leave everything exactly as it is for a couple of weeks to see for sure that the fault is fixed, I mean if you mess with it now and the fault then comes back it will just add to the mystery.

Of the four items listed above only the “brown tape” might have played some part in the problem IF it were an insect/mouse that was setting the alarm off.

Dec

 

[allias]

Oh no... problem is back. I guess the only option is to find someone with Star to scan it properly...

...or disconnect siren for good.