My w210 (E320, 1996) Won’t start
 

My problem is as follows:

I turn the key - and nothing. Won’t even crank. My battery is new any fully charged.
The head lights do not faint during the attempt. Other electrical equipment looks fine. After several attempt usually the car starts. It cannot be the imobiliser, since the car should crank even though the key has not been identified by the system. I’m suspecting than the sensor for the gear shifter is faulty (any one know where this one is located). Any suggestions?


Thanks in advance

Did you try "N" ???????????

Sure did, however did not help.

I had the same thing happen on my 1996 E320 last year. It turns out that the relay module inside the engine compartment passenger side needed to be replaced. To get to it you have to remove the 4 philip screw holding the lid and the module that has the fuses is the one that has the relays. One of those relays is your starter relay. The entire module that holds the six relays needs to be replaced.

relay
 

it is the K40 relay, the seem to fail quite often. it is in the pass side fues box, it has fuses plugged in to it. if you apply 12 volts to the large purple wire the starter will engage.
Ray
mercedessd@cox.net

This really interesting information. I have post this issue several times without any suggestion on resolution. Bear in mind, that most often there is no problem on starting. Did you guys experience the same? How much did you play for the this part? I have enclosed a link with a picture of the module in question. Please check if it is the module, within the red circle, that you are referring to!

Link to picture:
http://hem.bredband.net/dimtri/

K40 relay
 

If you remove the plastic cover, and resolder the cold joints it may work again. Norm in FL

Not mutch to solder here : http://hem.bredband.net/dimtri/images/spool.jpg

This module looks fine...

I have the same problem with my 2000 E320 and it happened a few times now. It started after a few trial of taking out and re-insert the key. Is the relay problem the only casuse of this problem? How much is the relay?

Dimmi, If you look on the other side of the green ckt. board. You may need an eye loop to see, there are some solder connections that do not make a conn. Norm in FL

When you say "the same problem" to you mean that the starter motor DOES NOT turn ? Becuse if it does, I understand that there might be an issue with the CRANKSHAF POSISTION SENSOR (several threads on that issue).
Regarding the price of this module - I will check on Monday. However, I reside in Sweden! In addition, I am not sure that your model has the same relay (bear in mind that my car is a 1996…)

Frankly speaking, I will not attempt any soldering projects on this module (even thought I got masters in electrical engineering :) ).
I will rather purchase a new module and hope that this is the issue. However, since this problem only occurs occasionally it will take some time before I can be confident that I have found resolution.

Nevertheless, I will keep you posted...

The price on this module is 1200 SEK in other words approximately 170 $. The funny thing is that you have to return my old one to get a new one…

I paid for the module $200.00 last January.

After further investigation today I concluded that the K40 module works fine.
I removed the plastic cover on the K40 module (http://hem.bredband.net/dimtri/images/spool.jpg) and check the relays during start. The interesting thing is that the position of the relays where the same during the those times when my car did not crank (starter motor does not turn). Thus I do not think your previous problem is the one I am experiencing right now.
The K40 module does not seem to have any relation/connection to the starter motor.

Was your problem really that the car didn’t crank (starter motor dead!) or was it rather that it cracked but did not fire up?

You've got to start at the starter, and work your way back through the components. Is the starter getitng current? If so, the unit is faulty and must be replaced. If not, where does the circuit lead to? I don't know, but my first inkling is that the starter is dead. Confirm that it is not before you begin tearing into other stuff.

Starter in not dead, the car most often starts without any problem.

My issue was both the vehicle did not crank on some occasions and it cranked but it did not started. But to confirm I went out to the vehicle and installed my old K40 and the vehicle cranked but it didn't start. You maybe right you may have some other issue, unless the K 40 has two of the relays one for the ignition and the other for the starter, but I'm not sure if this is the case. Perhaps someone can let us know the systems that each of the relays in the K40 controls?

Norman

Thanks for the info and your confirmation. You are right I really need to know if there is any direct connection between the K40 module and the starter motor.

Anyone knows?

Replaced the ignition switch
 

I have now replaced the ignition switch on my car. After five days the problem has not occurred. Just keeping my fingers crossed and hope that this is resolution…

Resolution !