Help with Mercedes W202 C200 - Immobiliser Stuck on

tunzafun001 on 03/06/2025 - 15:31
Last edited 03/06/2025 - 16:12

My parents old Merc (late 90's) Infra red only remote didn't work.
They got stuff out the boot using the key instead. Replaced the fob batteries. Did a resync procedure. Doors now open / lock fine with the remote… BUT..

The rearview mirror flashes green and red alternatively and the car will not start. It cranks, but won't fire.

Pulled stuff under the dash off. I found a factory Siemens immobiliser unit, but no other alarm or after market security.

The car cranks, which means the ignition lock is happy, but a signal isn't getting to the immobiliser. Looks like it shuts off
the injectors and coils

Read 100's of webpages, youtube vids and redits. Going in circles. There is a way to bypass the immobiliser, but the forum posters are all secretive about it. That was back in 2009. This car is now old….no one is stealing it, nor will anyone use this method to steal a car.

Try pulling a Merc dash and floor apart….and you still need the IR key anyway to release the steering column.

Rang Merc direct. They no longer have anyone who knows anything about the 90's cars!

So the car has now been sitting for 3 weeks, mid driveway.

I'm hoping someone here has done the bypass, or knows where to find some wiring diagrams the 1996 W202 C200. I'm guessing we just need to power the immobiliser relay permanently..just need to know what relay that is and where.

Cheers all.

Automotive Car Mercedes-Benz

Comments

  • mapax on 03/06/2025 - 15:48

    Unresolved Reports
    1 for Illegal/Banned Item
    Last reported 12 min ago

    lol at the reporter.

    Sorry I can’t help tunza, but you know what’s really shit? All the scumbags on the streets with canbus/obd hacking tools that can easily bypass all kinds of immobilisers yet the dealerships pretend it’s the hardest thing ever or that they can no longer do it.
    A friend had his Rav4 stolen last week and another had an old Vitara stolen a few months back.

    • tunzafun001 on 03/06/2025 - 16:11
      +2

      This is true.

      My parents are near 80.

      Their pride and joy brown Merc wagon is worth nothing. No one is going to steal this now. Everything is perfectly working….except for an immobiliser.

      If we can't find a way to bypass the immobiliser (still need the IR key to get in and release the ignition lock), then this thing will need to go to scrap. Pensioners will have no car.

      That is the true crime here…

  • brendanm on 03/06/2025 - 16:18
    +17

    This particular problem drove me CRAZY for a year! I had the red green red lights flashing in the mirror. I could crank but not start my 1995 C220. I thought it was an immobiliser issue. I replaced the fuel pump, fuel relay, fuel regulator, crankshaft sensor, sent the Engine Control Unit (ECU) to America for modification (immo off) got the MB dealer out (who couldn't diagnose the problem or even read the codes BUT still charged me $190! From checking many,many websites and Youtube I finally found one comment - just one line that said check your Over Voltage Protection (OVP) Relay. (relay in that silver box with the fuse next to OBD port).

    I did and that was it! That was my problem fixed! Easiest way to check the OVP is to open the relay case and push the bottom relay with a plastic pen (with key in position 2) and you should hear the fuel pump and injectors come to life…and you can start your car. Order a new OVP relay (around $100) and you are good to go!

    I hope my post helps someone as this was a major, major issue for me and i hope I can save another member from all this heartache! I was about to junk my car and send it to the wreckers as no one - not even the MB Dealer could diagnose the fault!

    From digitalkaos forum.

    • CheapandUsed on 03/06/2025 - 16:40
      +13

      The world is much worse off with the declining popularity of forums

      • brendanm on 03/06/2025 - 16:42
        +7

        Way better and easier to search than Facebook groups.

      • Clickbait on 03/06/2025 - 19:07

        Way way better

    • tunzafun001 on 03/06/2025 - 16:57

      Unfortunately the fuel pump runs. It isn't the OPV.

      Injectors and coil disabled. Ie. Immobiliser hasn't got the signal from the ignition to turn off.

      If I can find a half decent wiring diagram for the W202 infra red only c200 (that was sold in Australia), then I'm set.

      • brendanm on 03/06/2025 - 17:12
        +1

        I could be wrong, but the immobilizer should check the key and send a signal to the ECU to tell it to run. I'm fairly sure Mercedes wouldn't have bothered going that far if you could do something simple to bypass it.

        There are ways to get the factory manuals, I've used it before for w204 stuff, it's possibly a small fee, I honestly can't remember.

        • tunzafun001 on 03/06/2025 - 20:22

          There's an infra red receiver in the mirror.

          If it's see's the rolling IR code it opens the door, and allows the steering lock to release.

          If the key matches the tumbler it will allow the engine to go to accessories, and signal the immobiliser to power the injectors, turn further and it will crank.

          The signal for some reason isn't getting from the receiver downstream to the immobiliser.

          Not sure if they released the wiring diagram showing what wires do what to the immobiliser.

          • sprocketoctopus on 04/06/2025 - 17:02

            @tunzafun001: Just a way out there suggestion -perhaps the receiver was the fault, not batteries.

            Perhaps try another receiver/rear view mirror from the wreckers?

            Other than that, I just don't know.

            • tunzafun001 on 04/06/2025 - 17:19

              @sprocketoctopus: Cheers for the thought.
              Yes, the receiver is on the list of checks. I'm 99% sure it's a relay inside the ignition security module that is failing to provide the communication to fire up the ECU…but I do have the receiver as a 1% back up check.Someone wrote a post saying the com signal doesn't have the current to clean the relay, and will eventually fail. Question is, how do you bypass/ short this relay? Its a sealed cast alloy module. I need to know which wire is the signalling wire.
              It will be an old school signal at least (ie. a few volts).
              The receiver (mirror) currently picks up the IR code to open the doors and release the steering lock, so I dont think it's the receiver…but you never know, Merc may have a seperate receiver inside there for the immobilser. So will keeo it up the sleeve.
              Cheers again

  • CheapandUsed on 03/06/2025 - 17:27

    You may have already found this thread but sharing if not
    https://forums.mercedesclub.org.uk/index.php?threads/w202-el…

    This seems to say that there is a circuit board in the siren that relates to the alarm and immobilizer.

    Probably worth a look to see if any connections are loose at a min.

    • tunzafun001 on 03/06/2025 - 20:24

      Only for models with alarms and external immobilisers. Unfortunately, no alarm fitted to this, and only the factory built in immobiliser unit.

      Thanks for looking.

    • tunzafun001 on 03/06/2025 - 20:30
      +3

      This is the problem.

      No one cares that there are perfectly working 30 yr old cars out there that are arguably still a better ride than many new cars.
      People worked decades at $5 an hr to buy such cars. Now it costs $2000 for someone just to look at it. Those $5/hr workers don't have it.
      Sadly, it's the tech side introduced to them that has failed.
      But, the knowledge around this has been lost (ie. This uses Star, where modern cars are OBD).

      • Ade99 on 04/06/2025 - 07:46

        Makes you think what the "modern cars" with Ipad screens stuck all over the dash will be like. Almost certainly after a decade the parts (and more importantly now) the Software will not be available…

    • tunzafun001 on 03/06/2025 - 20:36

      Thank you for your time.

      You can hear the fuel pump running on their car. From my understanding, if the OVP is faulty then the fuel pump won't run?

  • Protractor on 03/06/2025 - 18:19
    -2

    If you do get it going,disable (bypass) all the security shit (if you can) and stick to manually opening doors, starting etc. Like you said no-ones go to pinch an obvious problem.Anyway your parents won't be driving for much longer.The roads are too bit a battlefield for octos.If you must make it less "pinchable" put a hidden inline isolation switch on the fuel pump circuit, somewhere under the dash, or a similar set up onto the starter solenoid feed wire

  • Clickbait on 03/06/2025 - 19:20
    -2

    I have a 2005 Chrysler 300C, derived fro the Mercedes W210. The original key was about to fall apart so I got a new key. These Chryslers will start three times with a fault key, then shut down. so after the locksmith left my car wouldn't start after two tries. He had re-coded my existing key in an attempt to fix whatever he had screwed up.
    He said it was a pre-existing problem, and he had no interest in fixing. So I found that I had a "Steering Control Lock" error, and have been up and down Google , Grok and Chatgpt. with no luck
    Two other Mechanics had a look and ran for the hills. Apparently I have to spend $2000 for parts to fix a software error that no-one can explain
    Thanks tunzafun001
    You have breathed new life into my quest

    • Protractor on 03/06/2025 - 20:00
      -1

      Bugger

    • tunzafun001 on 04/06/2025 - 22:08

      @clickbait Might possibly be a shared solution here.
      Does your key fob have a RFID chip that fell out? New fob won't have the correct RFID.

  • Protractor on 03/06/2025 - 20:06
    -1

    Looking fwd to seeing how AI solves problems like this, if the humans with the know-how are long gone.

    • tunzafun001 on 03/06/2025 - 20:42

      Put human into the car, crush the car. Make more AI.

      • Protractor on 03/06/2025 - 20:53

        I'm easy,it's your car.

  • mshanann on 04/06/2025 - 01:47

    Check Commandonline.co.uk or Vagtronics.co.uk. Offer cash.

  • Bart29 on 04/06/2025 - 08:30
    +1

    Hi,
    Check inside the key fob to make sure the imoboliser chip is still in place. It may have fallen out & won't start as it doesn't recognise the key without it.

    My car key fob needed a new battery and I changed it myself.
    Tried to start the car, started no problem, but cut out straight away.
    After roadside assistance couldn't find the problem, I got a tow to my Mechanic & after checking all fuses, starter motor & whatever else he could think of, checked the key fob & the chip was missing.
    Found the chip on my lounge room floor. Got him to him the next morning & started no problem been good as gold ever since.

    Good Luck, let us know how you go.
    Cheers

    • tunzafun001 on 04/06/2025 - 13:38

      Cheers.
      That would be a newer remote with RF (radio) and IR. This car is just IR only.

    • tunzafun001 on 04/06/2025 - 22:12

      @Bart29
      Might be something in this. Another user below pointed me to a document that shows this IR only remote does have an RFID chip on the back side of the key fob holder. I just assumed since it isn't an RF remote, it won't have RFID. But its an in-between model…they were just starting to introduce RF via this chip. Might be it.
      Cheers.

      • Bart29 on 05/06/2025 - 20:32

        Hi tunzafun001,

        Hope you get it sorted soon, must be a pita having the driveway blocked.
        Let us know how you go.
        My car is a Mitsubishi Lancer 06 auto wagon if maybe you or any one else was curious to know.
        And yeah the immobiliser chip is tiny, about the size of half a finger nail.

  • atrolgehapis on 04/06/2025 - 08:48

    If you've exhausted options and are looking for a mechanic and are in Sydney, Serge from Merctalk in Botany is great, and regularly works on older cars.

  • shirtz69 on 04/06/2025 - 12:55
    +1

    get a haltec?

  • Grunntt on 04/06/2025 - 14:23

    Doubt it's this simple but someone posted at Benzworld

    The first thing I need to figure out is exactly how the immobilizer (security) system is supposed to operate. The battery in the trunk was bad and the batteries in the remote fob were dead. Both were replaced. Even though the starter spins the engine over really fast…
    …Finally to disable the immobilizer and get the engine to start, I had to close all the doors - then use the key from the outside to lock the doors - and then use the key to unlock the doors. After just a few tries with it sputtering and dying it finally started up and kept running.

    further along in the thread someone also posted -

    there is a procedure to follow if the battery in the fob goes bad or is removed. This is described in the owner's manual but not obvious. Once a good battery is installed in the fob you must point it at the mirror and click the fob twice, then within 30 sec you need to insert the key into the ignition switch and turn it to the #2 position (on/run). That action resets the anti-theft function.

    Also DigitalKaosForum - check OVP

    I finally found one comment - just one line that said check your Over Voltage Protection (OVP) Relay. (relay in that silver box with the fuse next to OBD port).
    I did and that was it! That was my problem fixed! Easiest way to check the OVP is to open the relay case and push the bottom relay with a plastic pen (with key in position 2) and you should hear the fuel pump and injectors come to life…and you can start your car. Order a new OVP relay (around $100) and you are good to go!

    • Protractor on 04/06/2025 - 14:30

      On page 56 it says the alternative, if this procedure fails, is to push it off a cliff.

      • Grunntt on 04/06/2025 - 14:31

        On page 56 it says the alternative if this procedure fails is to push it off a cliff.

        A month or so after taking out an agreed value policy I assume.

        • Protractor on 04/06/2025 - 14:32

          Either way, it sounds like a win.

    • tunzafun001 on 04/06/2025 - 17:24

      Cheers for looking.
      Already been through these unfortunately. Key bit of information will be a wiring diagram (and ideally a schematic of the immobiliser unit itself).
      Sadly, second part is somewhat accurate. If someone breaks in / sets off the immobiliser… and like this, it doesn't release. Then the car is technically a write off.

  • Grunntt on 04/06/2025 - 17:40
    +1

    haven't spent any time looking but maybe something here?

    https://wiki.rusefi.com/Vault-Of-Mercedes-OEM/

    • tunzafun001 on 04/06/2025 - 18:56

      Nice one… I'll have a look through.

      • Grunntt on 04/06/2025 - 20:05

        There also may be something here.

        https://www.scribd.com/doc/279970157/C200-Wiring-Diagram

        Maybe something here too - https://autokeymaster.ru/fbs2-mercedes.html

        • tunzafun001 on 04/06/2025 - 21:00

          Ooooh..nice mate 👍

          Guessing I need to sign up to download from scribd?

          • Grunntt on 04/06/2025 - 21:11

            @tunzafun001:

            Guessing I need to sign up to download from scribd

            Haven't used it for anything myself.
            It may be worth a visit to those alternative places for an evaluation copy before you have to spend money on something that may or may not be what you need.

            • tunzafun001 on 04/06/2025 - 22:13

              @Grunntt: That second link is a gem. Huge thanks for that one.

              • Grunntt on 04/06/2025 - 22:15

                @tunzafun001: Hope it helps. I see what you mean about the general lack of useful information out there.

                • tunzafun001 on 05/06/2025 - 14:23

                  @Grunntt: I think it's due to not understanding the correct terminology.
                  I was looking for 'immobiliser' when I needed to be searching IFZ, EIL and EIS, HFM.

                  Your links helped greatly with this.

                  I also looked up some car clubs (that do motor swaps), so need to fake the Merc security/ CAN signals. Also got insight from car theft. These guys are the mechanics we really need!

                  The old join a few wires / Bypass an immobiliser is now generate a CAN high/ low signal down x wires.

  • 2esc on 04/06/2025 - 19:23

    A couple long shots to try.

    From what i understand the batteries in the remote are to operate the central locking and have nothing to do with the immobiliser.
    The presence of the remote fob in the ignition switch disables the immobiliser…

    Open the remote and inspect the coil at the end of the key, if the key is dropped then the coil can be damaged so key wont work in the ignition ( a mate worked in the UK for a while and his merc (Different model but in the 90s) had this problem.

    The other long shot is disconnect the alarm siren, its located (should be) behind the front wheel arch liner on passenger side there is a plug in the back of it, it could possibly play a part in the problem so best to disconnect it.

    Contradictory but batteries in the alarm could also be flat (Different car but our Audi tt had corroded batteries even the wires were rusted for several inches).

    Its a long shot as the alarm shouldnt talk to the immobilizer but its worth a look.

    • tunzafun001 on 05/06/2025 - 14:17

      Cheers for this.

      Not sure what you mean by coil at the end of the key?

      It's just a return spring for the flip key around a pivot.

      BUT.. as per a link from the comments above, I did see they do have a chrome ring at the start of their ignition. I thought this was just decorative. But looks like it is a RFID aerial. So will need to check inside key to check the chip (apparently the size of a grain of rice)!

      As for the alarm. I looked under the dash and engine bay. Never thought it could be in the wheel arch. There is no alarm sounds, but I'll put it on the list to check anyway.

      Let me know about the coil.

      Cheers

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