A headscratching key/ignition problem - Mercedes Benz SLK Forum

SLK R171 General Discussion SLK 200, SLK 280, SLK 300, SLK 350, SLK 55 AMG

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#1 Old 1 Week Ago
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A headscratching key/ignition problem

Hello all,
I have a headscratcher for you.

When I put my key into the ignition and turn it, itís approx. 50:50 as to whether it fires up straight away (ie that the starter motor turns). If it doesnít then I switch back to off and back on again and itís 50:50 again. So it does always start eventually but I have no idea whether itís going to be on the first, second, third or fourth go.

I should add that thereís no problem firing up once the starter motor is engaged but sometimes it seems like the message isnít being sent to send the electricity to the starter.

Since it does always start, I can kind of live with it but it would be nice to just be able to twist and go. Plus Iím guessing that whatever is causing the problem might eventually fail permanently and then Iíll be stuck somewhere.

Iíve done a search but it doesnít seem to be a common problem. Has anyone else experienced similar and resolved it?

Thanks guys!

Chicken
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#2 Old 1 Week Ago
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EIS needs replacing

Electronic Ignition System

Electronic ignition system is the type of ignition system that uses electronic circuit,usually by transistors controlled by sensors to generate electric pulses which in turn generate better spark that can even burn the lean mixture and provide better economy and lower emission.

some threads from our site seaarch

https://www.google.com/search?ei=hIN...rPgtO_QyY&ved=


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#3 Old 1 Week Ago
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I will start by scanning the car with xentry/das, and see if any errors are present, then you can do the test for eis, autorisation etc.
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#4 Old 1 Week Ago
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Sarge, it also could be the transponder chip in his key. @Chicken, have you tried another key?
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Before you go for EIS...

Try spare key.
Try new fob batteries.
Clean key.
Clean ignition where key goes.

There are threads: https://www.slkworld.com/gtsearch.ph...%20start%20car
It's one of those item where you have to word play to get a list.

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#6 Old 1 Week Ago
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Wow - you guys are the best! Literally one toilet break and four replies already!


Jeff, there's no issue with the running of the engine once it gets started - it's just getting the signal to the brains in the first place that I want to start the car.

i860, good idea - she's (over)due a service so I'll have them run for error code.

Mensra, it does the same thing with both of my keys (both with new batteries) so I suspect the issue is more likely to be with the car rather than the keys.

Avel Du, thanks for the suggestions - I've tried all apart from cleaning the ignition switch so I'll give that a go!
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#7 Old 1 Week Ago
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I thought the key Transponder was passive - i.e. doesn't need battery power, a bit like the RFID chip in a credit card.

Certainly I recall opening my car with the metal blade key and starting the engine (2006 R171) when my battery was flat and wouldn't unlock
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#8 Old 1 Week Ago
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Just to add, it sounds exactly like the problem that Guentha had here (https://www.slkworld.com/slk-r171-ge...turn-over.html) where the solution was to clean the socket with a q-tip and some alcohol so I'll give that a try and report back!
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@MarkChat Yes, the transponder is battery-less. It is an RFID type system. Cleaning the interior of the ignition switch assembly is not going to affect that. IR in the key is used for opening the top through the factory installed option if he has it. I think at this time, heís looking at some diagnostic system analysis. DAS/STAR.
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Never hurts to try the free/cheap options first.

If you get it scanned make sure it is the MB system.
This is more likely to get to the bottom of the issue.
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#11 Old 1 Week Ago
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Also check battery terminals including acc connection. Had a similar situation in that if I turned the key to ignition and waited a second, then turned to start it would trigger.

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If you hear the steering column unlock, the transponder is working fine. That sounds comes as soon as you insert the key, no twisting required.

You need to watch the "terminal 15 - terminal 50" actual values to see if the EIS is detecting the changes as you twist the key. Terminal 50 is the "start" position. This should be be a good clue.
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#13 Old 5 Days Ago
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Update:

I cleaned the ignition switch with a couple of q-tips (a bit dirty but not that bad) and she fired up on the first go.

However, since it was 50:50 before, I might have got lucky so I tried a few more times and....... it's still 50:50 😞

BUT...I then realised I've been putting the key in and turning all the way over in one move. Between what Osi and efair said, maybe I was doing it too quickly for the EIS?

So I tried Osi's delay method. I turned the key to the second click, then put on my seatbelt, then turned to start and it's fired up first go each time since Friday night.

So I've not fixed the "problem" but I've found a workaround that isn't too inconvenient - do the engineers here count that as a win? 😄
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I'm having the EXACT same issue and found the same work around. I'll delete my other post and follow this instead. Bustin' out the Q-tips at lunch.
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I always say a Hail Mary before I turn the key and never had a problem. Always chalked it up to the Holy Virgin but hmmm.....not sure anymore.....
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I'm always chuffed to be useful. This one will go on my tombstone.. ' here rests Osi, discoverer of the delay method'.

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It's now known as the "ODM". Here's how to use it in context:

A: My car doesn't always start when I turn the key.

B: Before you go down the expensive route of replacing parts, have you tried cleaning the ignition switch and employing the ODM?
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I have a similar issue with my just bought '05 slk55. The steering unlocks but engine doesn't turn over. If i try it repeadedly it works. I remembered the previous owner mentioned an issue with one key so i tried the other and its ok now. I assume a weak battery in key but i guess thats not it. Going to dealer next week for 80k service will ask them to check the key.
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#19 Old 5 Hours Ago
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Quote:
Originally Posted by jpm995 View Post
I have a similar issue with my just bought '05 slk55. The steering unlocks but engine doesn't turn over. If i try it repeadedly it works. I remembered the previous owner mentioned an issue with one key so i tried the other and its ok now. I assume a weak battery in key but i guess thats not it. Going to dealer next week for 80k service will ask them to check the key.
They need to run a star diagnostic on it, it could be you have an intermittent transponder chip in the fob. It also could be a weak EIS transponder coil, $$$. The transponder chip in the fob, as previously noted above, does not use a battery. So a weak fob battery would not cause this to happen.
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