Out of the blue, my wife's ML320 won't start. It cranks strong but won't fire up.

After searching the forum for similar problems, looks like fuel pump relay is logical place to start. Ordered one from my favorite supplier here in Virginia. She had to order it from California though....

My question is she said it looks like a relay that serves a lot of functions besides the fuel pump. I checked on the web and the description from a supplier below is what I found:

"Parking light : Horn : Fuel Pump : Blinker : Starter Motor : Circulating Pump : Foglight : Rear Defroster "



Looks like a multipurpose relay alright. But can the fuel pump function in this multipurpose relay go bad alone without the rest going bad as well?

Or am I replacing the wrong part?

Also, if it's not the relay's fault, where should I look next, and next after that?


Pls. help!!!



thanks!!

It may be a problem with the DAS function of the key. Using your other key may allow it to start, in that case the key you have been trying is "bad'.

Gilly

have you attempted to jump start her?

Battery?

Gilly

I'm going to check if the fuel pump is functioning or not.

Gilly, how do I diagnose this? Will I be able to hear the pump buzzing when I turn the the ignition on?

I understand it's beneath the left rear seat.

Have you tried the other key or not?

Gilly

No, Gilly, I haven't. I bought the ML used but had only one key.

I had a second key/remote combo cut but have not had it activated by a dealer yet. So I saw no need to try it.

By the way, what is DAS and how does it affect the keys? Frankly, I think Mercedes has gone too far here. I can't think of any benefit this gives the owner. If it is to prevent theft, how is it activated?

Thanks,

Jim

OK first of all, the dealer only has to activate the new key to get the remote unlocking/panic alarm to work. It will start the truck "right out of the box" just not unlock it. So DO try that first, worth a shot.
If there is a DAS problem, when you attempt to start it, you will normally see "start error" in the odometer, so watch for that too.
There is one other way I know of to check for DAS release (approval to start)
DAS is "driver authorization system". Many manufacturers use systems similar to this now, such as GM's "TheftPass" and "TheftLock" systems.
The chrome ring around the ignition switch is an antenna. It receives information from parts inside the key called a "transponder" (It's only vaguely similar to the transponder aircraft use to report aircraft identification and altitude info to radar units). The transponders in the key emit a fixed code, for key identification, and a rolling code (like garage door openers) for security authorixation to start the truck. On this particualr model, if there is a problem with authorization (like a transponder is shot, hint hint) the engine will get the authorization to crank, but the engine management system won't be authorized to operate. The starter operates to the end of the tip-start cranking time (I assume you know that the engine usually starts itself using tip-start, if not, ask for more info) and then stops cranking.

If you try the new key with no luck, then in answer to your previous question, you can remove the engine trim cover (just pull off carefully) and you will see the fuel rail. There is a brass covering over the fuel gauge port, has a schrader valve under the cover (don't lose the copper seal ring). A gauge can be put on the schrader valve, or as a simple test (be careful here) push in on the center of the schrader valve core and see if there seems to be pressure. The gauge is a better way of course, most people don't have one in their back pocket though. If you push in on the schrader valve core and "0" comes out, you can bet that you're on the right track. If "something" comes out, the results are a little inconclusive because you know something is there, but you don't know if it's enough for the engine to run on. Just don't get gas in your eyes, use goggles or something.

Gilly

Dear Gilly i have the same situation. my question is if the DAS don't recognize the key code it will stop giving instruction to the fuel pump to pump ???or the fuel pump in any case it shall pump fuel

i have only one key so i don't have the option to check if the key is valid, how shall i diagnose if the key is bad or its the fuel pump? is there any way to check if the car (DAS) is still recognizing the key code?
please help.

No telltale signs from the dash panel (and odometer), Gilly. I guess the original key is OK.

So it's off to check for fuel delivery like you said.

BTW, I would have had the truck towed to the dealer days ago except for a peculiar dillemma. It's in an underground garage w/a verrrry low ceiling and....... you know the rest.......

I'm checking to see if one of those "low-rider" towing trucks might be able to do it w/o scraping the roof off the ML! shish...!

If it gets complicated, I'll have to hijack a mechanic to do the work
on the spot.

I'll let you know what comes up. Thanks, Gilly.

Jim

Try the other key anyways, I've had them where you won't get the warning in the odometer.

Gilly

Gilly,

I forgot to say that I will try to start the truck w/ the second key before checking fuel.

Crossing my fingers this will work. Thanks.

Jim

Sounds good. Just unlock it with the key you have already (the one that won't start the truck) and try the new key in the ignition.

Gilly

Gilly,

No luck on the truck starting w/ the spare key.

Proceeding now to check fuel delivery.

Actually, Gilly, I'm just gonna have the pump replaced. Let you know what happens.