After getting a w212 2010 e250cdi manual 6 speed eclass
a few years ago as our dream car, the clutch going a week later should have put me off but we pushed on and didn’t give it back to the garage
multiple problems later and a few years
the turbo went at 120k
a man changed it for around £1300 (refinished the turbo refitted )
the battery was flat we put on a new one and it was turning over
stupidly I took out the relays without taking a pic first
i thought if they fit that meant they worked (how naive)
I’ve spent the last 3 months looking at front fuse box images,
relays
my heads blown, I don’t even know why I pulled it out as it was turning over now it won’t turn over
it originally just had grey and black ones
but I took some off a friends c250 that’s lead up
i don’t even remember all the holes being filled with relays like his was when I lent some

if someone could just tell me what relay goes where that would be brilliant ie you need …. This relay pic or link for fuse box letter K this relay for fuse box letter J

its a lot to ask but I’m just so stuck

here’s the box full with random ones that just give ignition lights
and it empty
and some just random relays I have
I have access to more



Originally it just had black and grey and I think one or two didn’t even have a relay in, the below relays are just some pics I didn’t realise just because it fits it may be wrong inside and

 

I have studied online configurations and relays for weeks and weeks and I still can’t get it right
please help

 

do you have the paper chart? I'd bet it is behind the small triangle shaped panel on the side of the dash panel.

 

WIS will provide diagrams of which relay goes in which slot. Each relay has a letter assigned to it and you can use the lookup table to see which letter is associated with each circuit. Once you know the location the relay of concern for starting. Try jump ing that relay location. They make manually switched relays which will fit into each location so you can turn the key on and flip the switch and the engine should turn over. If it does so then it tells you it was a problem with the trigger circuit. If it does not turn over the problem is not with the trigger circuit is somewhere in the power to the circuit under question.

 

Josh,

No worry, I will help you.



Not all relays are used in each car, even though it may be installed by MB.

Observe with care, which relay must be a 5 pin. Relay Q and M.
For relay M do not ever get a wrong 5 pin. Below is your relay M. P/N A 002 542 76 19. This is for engine starter.

The diode there at the pin 87 is to reduce high voltage spike when starter solenoid have stop.
The resistor between pin 85 and 85 of relay coil is used to reduce spike from the relay itself to car electrical system. All MB relay uses this special relay with clamping resistor.
DO NOT USE COMMON RELAY which DOES NOT HAVE the clamping resistor.
The voltage spike can be up to 300+ volts whenever an electromagnetic coil is de-energized and that magnetic field collapsed and has to discharge itself.
The ignition coil works the same way with a secondary coil where 20,000 volts can be produced.
See below a common relay with no clamping resistor or diode at pin 86 and 85, see its spike at 388 volts



MB relay with clamping resistor at pin 85 and 86, spike only 72 volts.





Remove this one below, do not use it. It has no clamping resistor. Also some relays pin 85 and 86 can be different location and that means pin 87 is surely wrong too and Kaboom !!!!



There is a high chance that unknown relay I marked red X is of the wrong pin assigment.




This is the danger when ANY relay pins are assumed as all the same position. See below. MB ones has clamping resistor between pin 85 and 86, but below is for pin location only.

See how some relays have different actual pin assigment of their 85 and 86 and thus 30 becomes effected.
85 and 86 are for the electromagnetic coils which pull down 30 and 87. 30 and 87 is the "switch" so to speak.
85 and 86 are like your fingers pushing down a push button switch to activate connection between 30 to 87.

....

I hope you did not YET blow up either your engine computer or the FRONT SAM computers inside fuse+relay housing itself.
The fuse+relay housing is called FRONT SAM and it has computers inside it.
This is what Relay N I marked X is for : Engine Computer

Pray hard nothing went wrong or your engine will never start.


=============================


As per my Front SAM, it would be the same as yours for sure, my part number maybe newer than yours, but these relays are the same type where I group them the same.

Relay, at Front SAM, position J, K & P A ----- 002 542 87 19 <<< a 4 pin relay with special extra wide pin 30 and 87 ( pin 3 and pin 5 )
Relay, at Front SAM, position L & N ------ A 002 542 72 19
Relay, at Front SAM, position M ------- A 002 542 76 19 << starter relay, 5 pin
Relay, at Front SAM, position Q -------- A 002 542 74 19 << 5 pin relay , for Start Stop B03 option
Relay, at Front SAM, position O & R -------A 002 542 83 19 <<< baby sized relay


=====================

PHOTO : Relay, at Front SAM, position J, K & P --------A 002 542 87 19 4 pin relay with special extra wide pin 30 and 87 ( pin 3 and pin 5 )








==========================


These are the duties for the relays for my car. It will be similar to yours and depending on your option levels.









Relay P and L is not in used in my car, but in UK with winter I am sure relay L is being used in your car.
Relay P may serve different use in a diesel engine.

==========================

See attached Fuse + relay housing document

Good luck...................

 

This is my front SAM after I audited its fuses and relay functions.











Fuses with white marker tape means it is not in use and I then have spare.
Those assist strings are for pulling out the fuses, I drilled a mini hole at fuse. Your car is RHD, you know how difficult the first 2-3 rows of fuses close to engine fiewall are to remove
where the wiper arms are blocking..

 

I forgot, there is a TSB for the baby sized relays they call micro relay, if for my car.

Relay, at Front SAM, position O & R -------A 002 542 83 19 <<< baby sized relay

See which relays are effected if for your car model and year
https://www.tsbsearch.com/Mercedes-B...54-15-P-057373

 

Attached.

 

Thank you all, especially the detail that you went in, I was blown away with the help you have given me.
thank you so so much it’s so appreciated.
it’s taught me two valuable lessons
1) don’t mess with relays unless you understand them
2) strangers will do huge acts of kindness and spend their valuable time helping someone they don’t even know

thank you

 

Come back to us when your engine can start and no issue yah.
Check all the fuses too when doing the relays

 

I did all the above made sure the relays were good, it gave me ignition lights
but would not do anything when going to turn over
i have a fresh battery on
and even used jumper leads ontop
i wonder if the front Sam is blown up
or maybe I’ve blown up the car completely (electrically) if so it’s such a shame
its been sat a while and it was a big decision to have the turbo done financially
the guy who did the turbo actually conned us then stopped speaking to us but that’s another story
is their anything I can do from here or is it now scrap worthy ?
such a shame as it’a in really good shape

 

Can you confirm this :
The engine WILL CRANK/SPIN but would not start/run or engine WILL NOT EVEN CRANK/SPIN ?

I would not declare total loss at the moment until you can check a 100% that all the relays ARE actually healthy and some big fuses at F32 Prefuse is also all good.
Also it could be some severe DTC which was triggered and which now either the ECM or Front SAM protects your engine and wont allow engine start until DTC being reset.
You need a decent mid class scanner like Autel 808 to scan the car, if not MB Xentry.
By now you need a proper workshop and an honest one.

Actually scanner price to the class of Autel 808 has gone down from US$1200 to now I think US$800 there about.
There are few variations of 808, depending on the prefix alphabeth and their capability also different.

 

Load testing a relay you need to load it at least 10 amps and see what kind of voltage drop occured and power delivery is stable and not jumpy-jumpy as in bad contact point of the relay.
Hearing just click-click-click sound is not good enough.
Like here : https://mbworld.org/forums/e-class-w...-not-know.html

Proper scanner dan do bi-drectional command, so you can tell to some degree that FRONT SAM and ENGINE COMPUTER is okey or partially defective.

How good are you electrically and what test equipment you have ?

 

Take photo of your "illegal" relay pins from bottom view with its ID number visible please.
I want to see what damage it can do or maybe just no connection......if indeed its 85 and 86 is not like MB original relay.

 

It doesn’t crank or spin when you turn the keys from ignition lights (which comes on ) it does literally nothing
I did have it plugged in pre this fuse relay situation and it had some error codes for the Sam unit hence why I started pulling relays

 

I am a bit at a loss with why you pulled all your relays from your working F-SAM.

I would advise you to....

1- backtrack to when all relays were untouched.

2- "battery reboot" the upset SAM's

3- clear all codes, drive 2 or more driving cycles

4- now *SCAN* and post the fault codes descriptions.

This may help us understand where the source of your problem may be.


FYI: "NO CRANKS" can get tricky with broken security or be as simple as brake switch, flaky gear selector PRN.

Read around the forum a little, I recall a 250-Diesel with a no-crank who found a nice quick-fix. I totally forgot what it was, perhaps a glow fuse.