Fried K40 relay or is it ECU ECM? - Mercedes Benz SLK Forum

SLK R170 General Discussion SLK 200, SLK 230K, SLK 320, SLK32 AMG

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#1 Old 07-06-2019
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Fried K40 relay or is it ECU ECM?

My K40 relay and ECU got wet, very wet.. in my '01 R170 230
I had pulled the battery negative for the winter. When I re-attached it this spring a ticking sound came from the control module box ( plastic box with ECU inside ). I grabbed the box cover and the ticking stopped. Once it was open I could see everything inside the box was soaked from condensation. The K40 relays, ECU, everything inside the box was soaking wet. I pulled the neg. again and dried everything out and cleaned with CRC cleaner. There was no obvious damage to the K40 board or the ECU board.

Now:
Turned to start position nothing happens; no crank or other sounds.
In position 2 all dash lights are on, engine cooling fan on high.
Cheap code reader that has always worked on slk and still works on other cars says " cannot communicate with computer".

Question:
Does the fact that the code reader cannot communicate with the ECU mean that the ECU is definitely fried or is it still possible the K40 could be bad?
Second: If the ECU is toast, does anyone know of any threads on replacing the chip so I can buy a used one?

Many thanks
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#2 Old 07-06-2019
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#3 Old 07-06-2019
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Check for voltage at ECU input.
I have a new contact that can Virginize ECUs if needed, although in a 170 I'm not sure that is needed.
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#4 Old 07-06-2019
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Quote:
Originally Posted by litlann View Post
In position 2 all dash lights are on, engine cooling fan on high.
That ^ is classic K40.
I take it that you've read 'THE K40 STICKY' posts 11, 25 ...
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#5 Old 07-07-2019
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Hi,

I have to agree with @M4rCu5 , and a lack of communication is very often due to the loss of one or more +ve feeds to ECU, which would make me look at K40 and all fuses related to ECU feeds

I am almost certain you would need to have a used ECU Virginised before you can synch it to the rest of the Immo, although I have never cloned the earlier ones, all V6 M112 R170's and other MB's with either CDI's or V8 / V12 ME2.8's that I work on here.

I think your Car has ME2.0 IIRC, @Turdo2 can likely confirm or refute that

I can now successfully clone the ME2.8's fairly easily without the risks associated with chip removal procedures

HTH, Cheers Dave
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#6 Old 07-07-2019
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Quote:
Originally Posted by Dave2302 View Post
Hi,

I have to agree with @M4rCu5 , and a lack of communication is very often due to the loss of one or more +ve feeds to ECU, which would make me look at K40 and all fuses related to ECU feeds

I am almost certain you would need to have a used ECU Virginised before you can synch it to the rest of the Immo, although I have never cloned the earlier ones, all V6 M112 R170's and other MB's with either CDI's or V8 / V12 ME2.8's that I work on here.

I think your Car has ME2.0 IIRC, @Turdo2 can likely confirm or refute that

I can now successfully clone the ME2.8's fairly easily without the risks associated with chip removal procedures

HTH, Cheers Dave
Oh Dave how I Love to refute your info!

I believe all post-facelift cars are ME2.8.

It is true that you will need to have an ECU virginized in order for it to get along with the immobilizer. Beckmann Technologies can do that for you, they are in North Carolina.

If it was me, I would get the whole set off ebay. Key, immo, and ECU!
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#7 Old 07-08-2019
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Dave2302, Turdo2
Thanks so much for the info.

Considering its purpose, would replacing the immobilizer be intentionally difficult? If so it may be above my pay grade. I can see your point of just replacing the key immob & ECU & being done with it; great tip thanks, I'll look into it. If the ECU can be virginized or cloned, that sounds pretty strait forward. I still don't know if I should try to replace the K40 first. When it stops raining I guess I'll try & see what I can figure out with a multi-meter. I'm on a budget so I hate to just through parts at it until it works.

Thanks to all who post
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#8 Old 07-08-2019
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Quote:
Originally Posted by Turdo2 View Post
Oh Dave how I Love to refute your info!

I believe all post-facelift cars are ME2.8.


It is true that you will need to have an ECU virginized in order for it to get along with the immobilizer. Beckmann Technologies can do that for you, they are in North Carolina.

If it was me, I would get the whole set off ebay. Key, immo, and ECU!
Hi Aaron,

That is exactly why I mentioned you, because I have very little knowledge of such specifics on 4 cylinder MB's

To OP, the way to confirm whether it is K40, Fuse(s) or ECU is to get the wiring diagram specific to your cars VIN, (from Mercedes WIS Discs), and then see whether all the powers and earths are present at your ECU

Work backwards from there if not

HTH, Cheers Dave
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#9 Old 07-08-2019
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Thank you Dave2302 for that very specific, detailed answer on K40 vs. ECU. Seriously thank you very much
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Even with the virginized ECU, I believe you still need SDS to finish the mating process. eBay or a parts car will be your best route in my opinion.
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#11 Old 07-08-2019
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Hi,

Yes you do need SDS to match a virgined ECU, but not a cloned ECU .................... (Not relevant here, but that statement would be incorrect if doing an engine swap like the V6 to V8's btw) !!

Right now, until the feeds / earths are confirmed, I think it is more likely K40 or Fuse, or a corroded terminal somewhere in between

Just in case you are a purist I would just advise that if you do go the used "Theft Relevant Set" route, your Car will report the wrong VIN every time it goes on a diagnostic

If it turns out to be dead ECU, the best way, (assuming she is indeed ME2.8 as we now suspect), would be to have your existing ECU's EEPROM Data dumped and cloned into a used ECU ................

Used ECU on it's own is always cheaper than the complete set :wink

HTH, Cheers Dave
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#12 Old 3 Weeks Ago
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Thank you, No (0.00) voltage @ ECU input. I don't have a wiring diagram but checked red/blue and red/green wires, which I believe are the power inputs to ECU. Also checked all other ECU input wires and no power there either. All k40 fuses check out ok. Only other fuse I know to check is #11 in engine compartment fuse box ( engine control 4 cyl. ) and it reads 12v with key turned, 0.00v with key out.
Don't know what to do next. Replace k40?
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#13 Old 3 Weeks Ago
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Hi,

Personally I like to verify by proper Diagnosis exactly where the fault lies before buying and changing parts

When checking for 12V and Earths I prefer a 5w test lamp, multimeters can report a useless "feedback" voltage because they do not load a circuit, the test bulb must light brightly

It does sound like K40 area, so first up (if you haven't already done so), get the correct Wiring Diagram for your Car's VIN, (Mercedes WIS diagram), "generic & pin out" type diagrams often lead one up the garden path !!

Check V Inputs and outputs to / from K40 using Wiring Diagram to find the appropriate pins / wires.

Strip K40 and Inspect the solder joints with a good magnification, dry joints show tiny cracks not always obvious to the naked eye, re flow them.

Test all the K40's relays, (Coils and Contacts).

Bell out Wiring between K40 and ECU for good continuity.

By the time you have done this you should know exactly where the fault lies.

HTH, Cheers Dave
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