W203 C220D Starter Fuse randomly blows (Front SAM)

Bit the bullet and had a specialist run STAR diagnostics. Turns out I was right, multiple faults in the Front Signal Acquisitions Module (SAM), as well as a couple of other minor faults that aren't presenting any real issues. The wipers decided to play up the morning I took the car to the garage, not working at first then randomly deciding to work a few minutes later with no issue, which I later found out happened to Mercedes when they changed the ECU about 3 years ago. They thought nothing of it and returned the car to my friend, who personally never experienced the issue.
As you can hear when it doesn't blow the starter fuse (Fuse 52) it starts fairly strong, keeping in mind I've been trying to drain the battery and heat the starter motor to see if the fault will present more often (it doesn't). No loose wires and working with a scissor jack in cramped spaces isn't very enjoyable for me so removing the starter to inspect wasn't really an option I wanted to consider unless I had to. Luckily I don't, but unfortunately fixing this is going to be far more complicated than I'd hoped.
Options at this point are:
Main Dealer Replacement - about £700 supplied and fitted (quoted by local Mercedes Dealer).
Third Party Replacement - £300-400 estimated, depending on cost of unit (Local Specialist).
Repair the thing - Difficult, Can't find schematics, High chance of failure, Lots of prerequisite requirements, Time consuming, but essentially FREE or a few quids worth of minor components.
Obviously I'm leaning towards repairing the unit, so my next task is to get the thing out (as well as the ECU as I have a feeling Mercedes never really replaced it), inspect the wiring and connectors, and then attempt to disassemble the SAM and see if I can locate the fault. I'll try to upload another video in the next couple of weeks to update on the situation, and a video of what I find if/when I disassemble the SAM. Hopefully this helps someone in the future.

[@0795omega]

After seeing this, fixed my problem, much thanks to you!

[@RichardMartin-it9xy]

Had this on my 2002 one. Upgraded fuses to 20. Was ok for a bit but had to carry a box of spare ones with me. Eventually diagnosed as starter motor problem. Changed it and been fine since.

[@kabantioksolomon4780]

Thank you very much. This was really helpful. Save me a lot of money.

[@godfreymandivheyi1721]

Thanks Bro, was in the same situation just now and bought a 20amp fuse after seeing your video, back on the road. You are a lifesaver

[@David-vb6yx]

Hello, I would be wary of increasing the fuse by too much. I know an extra 5amp doesn't seem like much but if I remember correctly the circuit was originally 10amp, however I read a Mercedes Service Bulletin which claimed it should have actually been 15amp and fitting the 10amp from factory was a little mistake. I only used 20amp fuses for diagnostic purposes to try and see how much current was being drawn when the fuse blows. A lot of the diagnostic procedure was not shown in this video. Watts law should be considered here; Volts X Amps = Watts. Since these circuits are 12v then a 10amp fuse would mean the circuit is rated at 120w (watts), following the Mercedes bulletin (15amp) the circuit was actually rated at 180w, but with a 20amp fuse you're now allowing 240w before the fuse blows. Fuses are there to protect the wiring (and circuits) behind the fuse. If I remember rightly (it's been a couple of years since I worked on this) the car had a 140w Starter Motor, meaning with a 10a fuse the Starter Motor would underperform ever so slightly and only cause issues as the starter begins to wear however with a 15amp fuse it would have plenty of current and work strong until an actual fault with the Starter Motor causes excessive current draw - at least in normal circumstances. However with a 20amp fuse the circuit is limited to 240w, meaning it would take a considerable fault to blow the fuse offering the rest of the circuits virtually no protection. I would recommend dropping back down to 15amp and, if the fault persists, replace the Starter Motor. -- Having re-read this comment after posting I feel I should probably clarify that I'm taking about the current draw from the Signal Circuit of the Starter, not the Starter itself. Starter Motors usually have a pretty much direct-line to the battery and require around 2kw (2000w) for this model of car.

[@mirozaradija6865]

Perfekt erklärt 💪💪

[@oguzkocakaya8352]

Teşekkür ediyorum benimde aynı pıroblemim vardı

[@florincostache8583]

Thanks you so much for your help

[@perom]

Thanks for the tip, you saved me😀

[@dhineshkumar8407]

Thanks a lot your video helped in my critical situation

[@user-rh2rc3ow8d]

Thanks dude! I just replaced it with 15A works for now. If the fuse keeps blowing i will be pretty sure that the starter is the problem.

[@ovidiumurgu8893]

Thank You, Sir!

[@themisu1988]

God bless you !!!

[@andiexzeon1610]

Thanks you

[@jdxtube68]

Does the 15A Fuse solve the problem? Or have you tried a 25A fuse instead?

[@David-vb6yx]

Sadly not, as you can see in the video it keeps "randomly" blowing that fuse no matter what size you put in there. I did strip the SAM and located a failing Current Sensing Resistor but couldn't get a replacement part in a reasonable timeframe, so unfortunately my friend had to get rid of the car. Signal Acquisitions Modules are definitely repairable, but are by no means easy. If you're competent with electronics repair and soldering I'd say give it a go, worst that can happen is you find the component you need will take 36 weeks to get! lol Oh and definitely get some very low melt solder!

[@okeyjokey981]

@@David-vb6yx I have the same problem with my w203. If I change my starter do I have a chance to fix this problem ?

[@jamesyoung7719]

@@okeyjokey981 did it fix your problem

[@okeyjokey981]

@@jamesyoung7719 yes it was the starter. From the moisture. I have replaced it with a new one. It cost me about 100$.

[@user-xy9qx9gn2s]

真的利害師傅……勁啊

[@karinarocha8948]

I watched this vid and switched to a 15 amp fuse about a year ago but now even the 15 amp is blowing, any advice on how to diagnose it now ?

[@David-vb6yx]

It would be either bad starter or the SAM (PCB that controls fuse box), the car in the video was faulty SAM. If you can get a known-good starter for cheap enough it may be worth replacing it to see what happens. If it's the SAM it will work out cheaper to get an independent garage to do it, as you need diagnostics equipment capable of reading faults to be sure and then recoding the replacement module. Absolute nightmare. I'm experienced in PCB rework so I was able to disassemble this one (very difficult, 10/10 would NOT recommend) and diagnose a single faulty component, but due to global shortages I was unable to source a replacement in a reasonable timeframe so the owner decided to sell it for spares or repairs. In your case it does sound like a faulty starter motor though, bad SAMs tend to pop fuses regularly but not every time. Only reason I increased fuse size to begin with was because there was a Mercedes Service Bulletin that said the original 10a was a tad over cautious, and that their techs were replacing them with 15a fuses if it ever presented an issue. Hope this helps.

[@AutoGlobalZone]

Where do you buy the fuse? Hardware store?

[@David-vb6yx]

I would presume so, yes. They're fairly easy to find, search for "Blade Fuses" on eBay or Amazon and you should be able to find a pack with lots of different ones (like the one I'm using, not sure if it shows in the video). The colour/number on the fuse is the Amps it's rated for, DO NOT change the value of the fuse on a circuit unless you know what you're doing, always replace like-for-like... Your car may take Mini Blade Fuses which are the same thing in a smaller size, they're cheap enough so it's probably worth getting a pack of each just so you have them.

[@AutoGlobalZone]

@@David-vb6yx thanks for your kind reply. That's quite helpful

[@AutoGlobalZone]

@@David-vb6yx Which one is you think starter fuse? Fuse that's maybe responsible if our car engine won't start?

[@i4ko95]

So what happened? Did you fix it? What was the problem?

[@David-vb6yx]

Front SAM failure, couldn't get the components needed to fix it at the time and the customer decided to sell the car as it was. Shame really I would have liked to have fixed it...

[@i4ko95]

Thanks for the reply!@@David-vb6yx

[@marionitu]

i’m having the same issue and i’d like a bit of help, i’ve got a C200 Kompressor 2001 Automatic transmission, once in a while one of them it blows but whenever I take the black one out and I put it back in and it works fine, but then a month later or so is doing it again and while driving but it does still work, it happened again yesterday morning and i’ve done that , came back from work and when I wanted to go shopping i’ve driven maybe 2,3km and that happened again and a few times since yesterday and it’s very frustrating, can you guys help me?

[@David-vb6yx]

The black ones (and the yellow ones) are relays - not fuses. A relay is an electronically controlled switch containing two circuits - one is basically an electro-magnet, when current (electricity) is passed over this circuit it closes the second (the actual switch) allowing current to pass through activating whatever component it powers. Relays control many different functions so it depends entirely on what the relay is for. By the sounds of it you most likely have a cold-solder joint (a small break in the soldered connection) inside the relay meaning that when it gets hot it's no longer making a good enough connection to allow current to pass through. Replacement of the relay would be the first step, if that doesn't help you really need someone who knows vehicle electronics to diagnose the issue as electrical faults are a nightmare at the best of times, and Mercedes are probably the worst of them all. These cars contains miles worth of wires, 5+ different control modules, fuses, relays, and a tonne of electronic components. They're unnecessarily complicated and if you're not experienced with electronic diagnosis or repair you'll spend months scratching your head and probably end up making things worse. Sorry I can't be of more help buddy, hopefully a replacement relay solves your problem.

[@marionitu]

@@David-vb6yx I’m not sure , i’ve changed the relay that i’m usually taking it off just to make sure , it was fine for a month and then it happened again yesterday so i’m not sure what’s going on , not easy to find a mechanic that’s experienced in the electrical/wires area , I live in Germany and where I live I don’t know many since I just got here couple of months ago, spoke to someone and they said it could be the computer being faulty and it needs to get fixed and it will cost around €300 not speaking in labour as well. The car isn’t really worth to put that much money in , it’s running well but it’s also quite old , if i’m being honest i’d just rather sell it on parts and just get something else , thank you anyway you was really helpful , hope i’m not too personal but do you have any socials i can contact you at? Thanks buddy

[@zandileyabo1535]

I have a c200 2005,does the same.. But when jump started it starts. Could it be the starter? Please help

[@David-vb6yx]

Could be either the starter, battery, alternator or earth strap. Test the battery voltage with a multimeter, should be just over 12v with engine off, if not replace the battery. Jump the car and test again it should read 13.8v or higher, if not it's the alternator. Then turn the car off and connect a single jump lead from the negative of your battery to a decent ground on your engine, you should find a metal loop thing that is used to lift the engine out which is best, if it starts you have a faulty earth cable. If battery and alternator are good and car won't start with the earth bypass then you likely have a weak starter. You could also try hitting the starter with a bit of wood or rubber mallet and seeing if it will allow you to start it, if that works replace the starter motor asap. Good luck 👍

[@duskojovanovic4372]

hey bro i have problem I have w203 2001 c200cdi Before 2 years I wanted to start car and nothing happened. I just changed 15 blue fuse and car started This morning same situacion I saw that 15 fuse blue is burned Ive changed the fuse and tried to start. Nothing happened. I put new 15 fuse and again burned. I dont know what to do, maybe some relay or something. Do you have any advice?

[@David-vb6yx]

You could try a new Starter Motor if you can get one cheap enough, if the fuse constantly blows I would think that's the most likely cause. Failing that it would most likely be a short somewhere in the wiring. Hopefully you get it sorted.

[@duskojovanovic4372]

@@David-vb6yx Hey bro, I put 20 A fuse (yellow) and car is working for now. I dont know schould I visit workshop to chech everything about that or?

[@jamiekelly8548]

My fuse not blown but key is dead after changing battery it won't work doors or boot ?

[@David-vb6yx]

That's a different issue entirely. It sounds like either key battery has died or it needs resetting. It's a simple procedure but it varies from car to car. Have a google, should involve putting key in ignition and pressing or holding door lock buttons...

[@kelkitli2961]

Merci

[@GFrecovery-repair]

my engine dosent start at all i found the fuse like that put a bigger but no luck... i am thinking is the starter... what u think about this?

[@David-vb6yx]

You could try a starter but best get it on mercedes diagnostics first, if you're getting front sam module error that's likely the cause

[@GFrecovery-repair]

@@David-vb6yx is a bit tricky because to move the car will cost me a fortune. I can hear the starter engaging but not turning… will take me bit of work to take the starter out but i will go on this route for now

[@David-vb6yx]

@@GFrecovery-repair if you can hear the starter engaging but not turning the engine then this may not be the issue. First thing to check is whether or not the engine turns freely, try to see if you can rotate the engine by hand with a socket on the Crankshaft Pulley, if it doesn't move with a long bar you may need a new engine, if it does then move on with diagnostics. Using a bit of wood carefully but firmly hit the starter motor, not hard enough to knock it off but firm enough to dislodge any shit that may be clogging it, always presume you've got a flat battery with non-starting vehicles and either use a jump pack or jump start with another vehicle. Mercedes have very complicated electronic systems, often you'll only get so far with standard no-start procedures and may require specialist diagnostics, but the fundamentals are always the same - you need rotation, compression, ignition, fuel and air for the car to start and run.

[@mansuransar5534]

Hi guys I had the same issue whereby the fuses kept blowing, so I started the starter old skool way with a long screwdriver 🪛 by touching both connectors on the starter. At first there was only clicks nd eventually started, I am of the opinion the starter just jammed. It's been working 100% ever since. Thanks Guys

[@hajileserpud9539]

@@GFrecovery-repair any good news to report soldier ?!?! I'm fighting a Mercedes E320 with same problem, any info is appreciated

[@krizzomo]

bei mir war es die zu schwache batterie, laden hat auch nichts mehr gebracht, eine neue musst her. beim messen der Spannung gabs nur 10,44V!

[@David-vb6yx]

Yes that's definitely a dead battery. Sometimes with a decent smart charger they can be revived, and sometimes excessively low voltage would require a top-up of the battery fluid if it's not a sealed unit. In my opinion, though, a new battery is the way to go as some come with a 3-5 year warranty which covers you in the event of battery failure for longer than you're likely to own the vehicle.

[@zakariah6380]

les matins du saison d'hiver je tourne la clé pas de réponse le moteur ne tousse même pas, mais quand la température s'élève un petit peu il démarre normaal,tu penses le problème vient d'où.

[@aslanburst3704]

Bougie de préchauffe 👍

[@jamala7013]

Regarde ton calculateur moteur j’ai déjà eu le tour

[@Peter-it5ht]

I have the same problem at the moment, I have had fuses blow, I can turn the key several times and it will not start ,I can hear a click everytime I turn the key , then it will start, it will be at the garage on the 16th Oct, I hope it will be sorted I will post what I the garage find.

[@gjergjkastro9404]

Hello Peter. How are you? I have same problem with mine a w203 2004 model automatic transmission. It started blowing the 15amp all the time when I tried to turn on the car. With my own risk I put a bigger fuse to handle the load. It worked for some time but now doesn't work any more. It gives a click sound but without starting the starter. I think the starter has problem with the carbon brushes. Is not problem with battery because I have tried with another battery in parallel without success.

[@David-vb6yx]

It really bothers me that I wasn't able to get this fixed. There is a global shortage of electronic components at the moment and so it was going to take too long to get the specific component that I found to be faulty. Because of that I had to call it a day and my friend sold the car as it was and brought a Lexus (much better car). I am fairly confident that, in my case, this was a faulty Current Sensing Resistor on the PCB of the SAM Module. Hopefully you have a simpler issue, that me. Best of luck.

[@chilldeepcs5234]

Hello, did you get it fixed? What is the problem? I got mine burning fuse 52 now aswell. rofl

[@Peter-it5ht]

@@chilldeepcs5234 Hi ,the problem was water leaking through the bottom of the screen and dripping on to the fuse box and the ecu,the lid on the fuse box still will not fit so I have sealed the screen and covered the fuse box with a plastic bag, I have not had a problem since. Hope you get yours sorted. Pete

[@tuomasranta2885]

@@Peter-it5ht Hey pete! I have the same problem. How did you make sure that there was water in the fuse box and how did you get rid of the water. I would appreciate if you could answer. Tuomas

[@naldiponari2583]

Like this problem but me have 200kompressor please help me

[@David-vb6yx]

Should be very similar. It's entirely your choice but I'd recommend getting someone to run Mercedes Star Diagnostics on your car, if they can confirm front SAM fault then thats what it is.

[@koolumar101]

Bad SAM I believe!

[@David-vb6yx]

Yes it was, just 1 faulty Current Sensing Resistor but due to the electronic parts shortage at the time I couldn't get hold of a replacement unfortunately and the guy needed a car. Really put me off Mercedes though the thing looked like it had been soldered together by a blind monkey with no hands!

[@SamsungAs-hh5ux]

Рахмет

[@serajsweed5570]

ياريت تزيل اضافرك لأنها تحمل الكثير والكثير

[@David-vb6yx]

One of the problems with working on cars without gloves I'm afraid 😂 they do get cleaned but having nails is convenient for many things

[@petarstanic9059]

Hello. I have problem with starting the engine. Mercedes w203 90kW 2.2cm³. No cranck. Namely, I got random malfunctions on the board like: -Display faulty. -coolant -ESP etc. So nothing of this isn't broken. Electricer said that ECU is broken, second one said that SAM Module is broken. Anyone had same or similar problem?

[@duskojovanovic4372]

speak serbian?

[@petarstanic9059]

@@duskojovanovic4372 reci😁

[@duskojovanovic4372]

@@petarstanic9059 jel si resio problem haha i ja sam pre par godina imao problem.. samo zamenio 15 osigurac plavi i vozi

[@petarstanic9059]

@@duskojovanovic4372 Trebao sam zamijeniti kompjuter motora, pokvario se pa izbacivao neke random greške

[@duskojovanovic4372]

@@petarstanic9059 au matori ma sve to zavisi od majstora tesko je naci majstora za mecku da je dobar i da ti kroz dijagnostiku tacno kaze sta je kvar