Immobiliser?! 1992 W124 300TD Estate

[gr33nmachin3]

First time poster here on this particular forum, but I frequent other forums and am chuffed that these forums exist! I looked through the 12 pages of posts using the search term 'immobiliser' and did not come up with a suitable answer, so I'll post this as a new thread. On to the details:

Hi All,

I have a new-to-me Benz (RHD 1992 W124 300TD Estate). I am having, from what I can tell from the research, a 'typical' problem with the car not starting, lights sticking on/flashing, until I mess about with the key fob. I've put in a new battery, but it is being drained either by the immobilizer/security system or I have a separate parasitic loss problem...HIGHLY unlikely given the known good history of the car.

I have searched for several hours for where to locate the electronic bits (ECU, wires, harnesses, relays, etc.) so I can PERMANENTLY disable the stupid immobilizer before I drive the car off a cliff. There are plenty close by.

I have seen the images on Mercedes forums and on Google images and on MercedesSource (great site!), but all of the images show the items I'm looking for either under passenger or driver's side of dash. My car has no such feature/s. Under the passenger side is a quite unassuming, but RED, harness that is for the air bags. Not gonna touch it. There is no other harness as some pictures show. There is nothing else under there but a steel panel that, once removed, shows that there is nothing hiding there but dust bunnies.

Under the dash on the drivers side are also no such black boxes or harnesses or anything that I can tell. I don't know if this is because the car is an estate and the stuff I'm looking for was moved to another location unique to an estate (like under the rear seat or in the boot) or what.

I hope someone can shed some light on this. I am also posting a similar post on the other forums I'm familiar with (peach parts, mbuk, etc.).

Thanks in advance! I think the car could be great, but at the moment it is an enormous pain in the ****!!!!

 

[Dec]

Is this a UK car?
What kind of a remote fob do you have? Describe it or put up a picture.
What kind of alarm siren is there in the car?
Have you tried to unlock the car with a key in the door lock or in the boot lock?

Dec

 

[gbjeppm]

Not sure on the 124, but it is likely that everything you are looking for is in the footwell in front of the passenger seat.

This thread should help, when I stripped mine out, I found that the fuel pump relay had been "switched", removed that an all was good.

How-to: Disable alarm on a 1993+ W124 - Mercedes-Benz Forum

 

[gr33nmachin3]

Not sure on the 124, but it is likely that everything you are looking for is in the footwell in front of the passenger seat.

This thread should help, when I stripped mine out, I found that the fuel pump relay had been "switched", removed that an all was good.

How-to: Disable alarm on a 1993+ W124 - Mercedes-Benz Forum

Thanks. See my original post. Nothing in the pass footwell besides SRS harness.

Fuel pump relay. I'll add that to my ever-increasing list of annoyances to check as I *try* to develop a relationship with this car. It's not making it easy on me!

 

[gr33nmachin3]

Is this a UK car?
What kind of a remote fob do you have? Describe it or put up a picture.
What kind of alarm siren is there in the car?
Have you tried to unlock the car with a key in the door lock or in the boot lock?

Dec

Dec:

1. Yes. UK car
2. Not sure but I'll check once I'm back at the house
3. Siren is not operable as far as I know. I'll snap a pic and post here (if I can as a new member).
4. Yes. Tried just about everything. All the doors. Lock. Unlock. Pressed the buttons on the key fob. Sometimes they work. Sometimes they don't. Next step is to get a new battery for the fob.

For whatever reason, a jump-start with cables always does the trick. Not sure what, if anything, this could mean. As I said, the battery is new as of last week, although it's probably knackered from being drained all the time. I disconnected it for now.

Cheers.

 

[Dec]

Let us know how many wires are going into the back of siren?
Is there a Red light in the cabin to indicate that the car alarm is armed when you lock the car?


Generally, with alarms that have a separate remote fob, when you unlock the car with the remote fob, you unlock the doors and you also disarm the alarm… which disables the immobiliser and allows you to start the car.

So, if you can start the car then you must have disabled the alarm and immobiliser so whatever you do, don’t lock the car again with the alarm remote fob or you will re-arm the alarm an the immobiliser.
Just lock the car with the key in the door or until you get to the bottom of the problem, it may just be the remote fob that’s faulty.

One other thing, usually, with these older alarms, when you reconnect a car battery the alarm will re-arm itself as it thinks the alarm system is being tampered with and the siren may sound and/or the hazard lights may flash.

Dec

 

[gr33nmachin3]

Let us know how many wires are going into the back of siren?
Is there a Red light in the cabin ...?

Yes.

Generally, with alarms that have a separate remote fob, when you unlock the car with the remote fob...Just lock the car with the key in the door or until you get to the bottom of the problem...

I only use the key to lock/unlock/start the car. The PO said that he has never had to use the fobs other than when the battery is swapped and/or cables disconnected. He had the car for 7 years, and his wife drove it for 2 years 80 miles round trip and never had the problems I'm having.

One other thing, usually, with these older alarms, when you reconnect a car battery the alarm will re-arm itself as it thinks the alarm system is being tampered with and the siren may sound and/or the hazard lights may flash.

The symptoms I've had when I try to start the car are:
1. Wiper randomly comes on.
2. Various dash lights light up or don't light up (ie: ABS light).
3. All corner/side marker lights come on and either stay on or flash.
4. Car will eventually very slowly turn over, even with a brand new battery, and eventually kill the battery or the car starts after 30-45 seconds of cranking.

The update for today is that I removed the glove box and found the LaserLine control box in there. It has been temporarily disconnected. There was also a cylinder in the left side of the glove box where it appears one would insert a key and that key would do something....but I don't know and the keys I have don't fit it. It is also disconnected.

I was hoping this would be the end of my problems. After disabling those items, I let the car run for 15 minutes then drove it for 30 minutes, some of that at motorway speeds. My hope was this would give the battery a decent charge. Charging it via the alternator is no substitute for charging it on a battery charger, but I was hoping for the best.

This morning I turned the key and it barely turned over, but it did start relatively quickly. The ABS light stuck on brightly, then it dimmed, then it went off. The wiper came on by itself and did a few swipes then turned off.

Do I perhaps have water somewhere it shouldn't be that is causing these electrical gremlins?

I did look under the rear seats, and sure enough under the driver's side rear seat water has infiltrated under the vacuum pump that controls the door locks. I'm fairly certain it's from the compromised rear window seals that permit water to leak down into various compartments. I digress....

Thanks for any insights.

 

[bolide]

Good luck searching for a fuel pump relay. The fuel pump is mechanical

Your problem is with the aftermarket alarm system

You probably have a bad cell in the battery and/or the alternator voltage regulator needs replacing

If the engine turns over slowly with a new battery then there's problem with the starter or wiring to it

Nick Froome

 

[Dec]

Tel us about the red light, when does it come on/go off?

This all seems to be a starting problem and seems to have nothing to do with an immobiliser, if it is an immobiliser then it wouldn’t start at all.
Open up the vacuum pump to help it to dry out and check that the vacuum pump electrical connections are clean and making good contacts.

The wiper fault may be a faulty N10 Relay …OR… a faulty wipers switch on the stalk.
See… N10 Relay, Soldering Repair, Wiper - Indicators & Hazards - Rear Window Demister. - Mercedes-Benz Owners' Forums

Have you fuses like the below, if so, ensure the are all making good contact.

Dec

 

[bolide]

Tel us about the red light, when does it come on/go off?

This all seems to be a starting problem and seems to have nothing to do with an immobiliser, if it is an immobiliser then it wouldn’t start at all.
Open up the vacuum pump to help it to dry out and check that the vacuum pump electrical connections are clean and making good contacts.

The wiper fault may be a faulty N10 Relay …OR… a faulty wipers switch on the stalk.
See… N10 Relay, Soldering Repair, Wiper - Indicators & Hazards - Rear Window Demister. - Mercedes-Benz Owners' Forums

Have you fuses like the below, if so, ensure the are all making good contact.

Dec

I don't think any of this is relevant

The only way to immobilise a 300D is to kill the feed to the solenoid or interrupt the fuel supply. If the car intermittently starts & doesn't start, and it has an aftermarket alarm / immobiliser, start there.

Does the engine turn over when it doesn't start? If no, there is an immobiliser. If yes, the engine's getting no fuel

If the vacuum pump isn't working the doors won't unlock. It could be that the vacuum fuel shutoff valve has failed, but they tend not to go intermittently "on"

Drying out the pump? It works or it doesn't

Wipers running when trying to start the car and the engine turns over slowly - classic symptoms of a dead battery

Nick Froome

 

[gr33nmachin3]

Sounds like starter/wire issue then. It's just bizarre because when I bought this car, it had been totally reliable for 2 years...then all of a sudden it's got electrical gremlins.

The battery is new...but perhaps it was not sold to me with a full charge and has not been fully charging since I've installed it.

I just did an experiment this morning. I started the car (with the 'very slow turning over will it ever catch' situation). I drove to Glasgow. I parked it and removed the ground cable and left the car to sit for a few hours.

When I returned and reattached the ground cable and tried to start the car, the battery was even less alive than it had been in the morning. (There is also a leak in the hand pump that primes the fuel filter, so air gets in and can cause starting troubles until I prime it again, but that is not an imminent cause of my starting problem.)

So it sounds like I need to find a multimeter and start testing.

 

[optimusprime]

If its a problem get it removed .I had to few weeks back .Went to the car .Spinning over but would not fire up . I did all i knew from the past problems i have had with cars ,plugs distributor ,leeds all the ideas i have in my mind . But in the end i had to call in this auto electric guy ,and he disconected immobiliser .First turn of the key it started up.

 

[gr33nmachin3]

Update: the laserline alarm has been disconnected. That has helped with *some* of the starting issues, but not all of them. The lights no longer go on/off, but now the wiper still goes on by itself and the car *occasionally* turns over quite slowly and sometimes it starts but sometimes I need a jump. Three days ago, I installed a new voltage regulator and was so certain this was the problem, but after driving the car several hundred miles this weekend, it has not started once and needed a jump and another time turned over but only eventually started.

When the car is running, according to my multimeter, the battery is at 13v. It's at 12 with the car off. So something is working with the alternator/voltage regulator, but either it's not working 100% or there is some other gremlin draining the battery while the car is turned off.

Any ideas are *greatly* appreciated.

 

[Dec]

You should open up that whole section under the wiper relay and see if anything is wet/corrosion.

Also check out the vacuum pump, open it up and check inside and perhaps leave it disconnected for a while to see If that has any effect on things.

Dec

 

[gr33nmachin3]

I see that you're keen on the vacuum pump/wiper relay theory, so just for you I'll give it a try ;-)

 

[gr33nmachin3]

Nothing wet or even damp in the wiper relay box area. Vacuum pump (under rear seat) totally dry and looked fine. What is your theory on the vacuum pump? The doors all lock fine from the driver's side and the rear boot/trunk gate, but not the passenger door.

 

[Dec]

This morning I turned the key and it barely turned over, but it did start relatively quickly. The ABS light stuck on brightly, then it dimmed, then it went off. The wiper came on by itself and did a few swipes then turned off.

Do I perhaps have water somewhere it shouldn't be that is causing these electrical gremlins?

I did look under the rear seats, and sure enough under the driver's side rear seat water has infiltrated under the vacuum pump that controls the door locks. I'm fairly certain it's from the compromised rear window seals that permit water to leak down into various compartments. I digress....

Thanks for any insights.

Because o f the water at the vacuum pump, I thought it could have been wet for a long time and caused corrosion.

The wiper relay controls the intermittent wiping so thought that might be affected by damp.

Dec

 

[grober]

I suggest you also look closely at all the main earth return paths especially the engine earth strap and its connections to the chassis. When trouble shooting electronics people often forget its not called an electrical "circuit" for nothing!

 

[optimusprime]

dont know

Google MERCEDES BENZE MODEL 124 M103 MAINTENANCE MANUAL .you will find a section in there at number 24 under electrical trouble shooting you will find a box you can change for the alarm checking. Its all in there but it can take some time to find it. It will come in for other things you will need.

 

[optimusprime]

Google MERCEDES BENZ MODEL 124 M103 MAINTENANCE MANUAL .you will find a section in there at number 24 under electrical trouble shooting you will find a box you can change for the alarm checking. Its all in there but it can take some time to find it. It will come in for other things you will need.

check it out