Hopefully this will help other to trouble shoot. Originally the car first developed a hard starting problem, beginning it was hard to start (had to crank it two or three times before starting). Then it wouldn’t start at all by itself, had to use starting fluid in the throttle body (take off plastic plate held on by 6 screws where both intakes join) then it would start. Changed out the crankshaft sensor and it was fine for about a week (started on first crank). Finally it wouldn’t start at all even with starting fluid (dies immediately after start), tested out fuel pressure at the rails and wasn’t getting any pressure. So I changed out fuel pump and fuel filter but still no pressure at the rails.

After some research on the internet, it appeared to be the K40 relay module is the culprit. Took out my board to investigate, however all the solders looked fine. Re-soldered most joints per instructions on the internet, plugged back in and car still wouldn’t start. Called local Mercedes dealer and they wanted $190 to diagnose the board, while I found new k40 relay boards on the internet for $185. No brainer there. Got the new board in the mail after 4 days, plugged it in and it started right up!

All in all, it costed about $600 for me to get the car running again. Probably would have been the same if I took it to the dealer, but now I got a new fuel pump, fuel filter, and crankshaft sensor. Think I will be changing out the cam shaft sensor, since a lot of people says that crankshaft and camshaft sensors should be changed at the same time.

 

SLK 230 won't crank?! No start error messages
OK, straight in with the issues!

We bought our SLK from a guy who had been left it in his uncle's will, bizarrely. It's done 85k but seems to have rusty arches all round. I am hoping to god that the underneath isn't rotten.

Anyway, the car started with fairly little drama the first time, with fresh fuel and a fresh battery on it. It spluttered a bit but got going easier than I had thought it would. Happy days.

It had been stood a couple of years at this point, or so we thought. It looks like it may have actually stood for up to 6 years, going by the date of its last service. The history was pretty regular up to that point.

So the car was left at a garage for an MOT test to see what needs doing. Unfortunately they couldn't start it. I found the fresh battery drained also. My OH mentioned that the car had seemed to get worse and worse for starting as our 250 mile journey home progressed, so I wondered if the alternator was knackered. خرید خدمت Leaving it overnight with a charged battery has seen no voltage drop, so I don't think there is a parasitic drain going on. Wiring in a multimeter in series also shows a max reading of just 0.15 amps, so doubt this would drain a battery.

Anyway, I digress, the starting issue: The car would not attempt to crank, but it did not show any start error type messages, which much research has told me can happen. I messed around a lot with the battery and cleaning the ends of the cables etc. No change. I then opened up the black box next to the battery to have a look at the K40 module. I took this apart and the board is spotless, no burned or damaged solder present.

I did notice that somebody at some point has added in a cable with an inline fuse holder to the wiring within the black box No idea on this, and also there is a purple wire been added in the engine bay which I suspect may be some sort of additional earth someone has added at some point.

Anyway, I pulled and inspected all of the fuses on the K40. No problems. I put it all back together and clipped all of the connectors back on and the car started first time!

I tried it again after we took it back home, and it started no probs. I thought I had somehow solved the problem. Tried it this morning and we are back to no attempt to start or crank. Can anybody offer any suggestions? Sorry for the long post.
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from my experience, if the car cranks and doesn't start, then it could be the k40 relay. however if it doesn't even crank, it could be something like battery or wiring.