w245 CDI euro5 won't start

[mattkh]

Hi everyone. Today won't start at all .

What is the temperature outside..?
Can you hear the fuel pump buzzing when you turn the ignition key..?

 

[Exp21]

18° C and yes I hear it

 

[Exp21]

Update: I had an intuition, I tried with the second key and started at first attempt. Honestly I don't know if it's a coincidence or it's compatible with symptoms.

I hope it was the key battery or the key itself not communicating properly with the electronic module. I checked the CR2025 battery voltage and it's 2.96V, probably a little low and it started giving these symptoms

 

[mattkh]

Update: I had an intuition, I tried with the second key and started at first attempt.

wow!
So from now on always use the second key.
If the problem occurs again, then we know there is something else that needs fixing.

 

[Exp21]

I'll keep the thread updated, but to be honest I don't believe that much in having solved the problem

 

[mersum1es]

Key battery has no part of starting the car. Inside the key is 'induction coil' type component which powers the key authorization, component can be loosen/bad contact on pcb.

 

[Exp21]

As I suspected, thank you.

The idea came to my mind going through the menus of my Autel, where I found a voice similar to "key authorization to starting = NO" and so it came the doubt. So, if it's the key the reason, I have to replace it because it doesn't authorize the engine to start. Am I right?

 

[mersum1es]

It might be soldered...

 

[Exp21]

In all youtube videos it seems that if key is faulty, it doesn't crank at all. Anyway only time will tell..

 

[Exp21]

After 3 years a similar problem is back.
I didn't replace anything in 2021. It came back to working fine. Now, days ago I had an event of cranking but not firing with warm engine. It started at 3rd attempt.
Now same story. No trouble codes. Car starts but not at first key turn, it requires a little insisting and when it starts, the engine works at very low rpms (about 400-500) like if it's going to shut down but then it revives and goes to a normal idle and works fine. No symptoms after the "problematic" start.

Do you guys think it's the crank sensor? With no codes it's hard to tell.
Car has 100k miles.

Thank you

 

[Exp21]

Edit: I replaced the crankshaft (CPS) sensor. It started fine for a few days, than the problem is back. Today I found the codes:

11C300 - The upper limit value of component B4/6 rail pressure sensor has been exceeded
140800 - The oxygen concentration in partial load operation is implausible (too high).

The 11C300 disappeared by itself after the car started again correctly (the error cancelled).
If anyone has a theory about, it's welcome.

Thank you

 

[mersum1es]

rail pressure in not triggering fault code during a start, but it might give a hint there is something fishy in pressure... fuel quantity valve is most common, unless it is injector excessive leak.

 

[Exp21]

Thank you. I'll wait for a MB dealer response about the diagnosis. One thing I don't get clearly: if an injector leaks, shouldn't I get an error for low pressure?
Thanks

 

[mersum1es]

sometimes you may get high pressure limit triggering even you have a leak; system overshoots when trying to compensate fluctuating pressure. True that then you usually have both low and high pressure alerts.