Bill Matheson

I have an 04 clk500 that's having no start no crank issues.
The key unlocks the ignition lock, and turns to the start position.
The interior accessories and headlights all work.
The battery tests at 12.4v.
I've checked every fuse, the starter wires, and changed key batteries.
The instrument cluster does not come on at all.
No clicks or anything when turned to the start position.
It seems like there is no power to the ecu.
All the wires, and connections appear clean and unbroken.
This just happened without warning.
No faults or idiot lights beforehand.
Any ideas?

Anker

As Rodney says, ECU not active until engine starts. You should check the starter circuits. I would start with the ignition switch and work from there. The circuits come together st the starter solenoid. There should be 12 V directly from the battery at the thick cable and 12 V from the ignition switch at the thinner cable when the key is moved to the start position. Not terribly complicated, but easiest with the help of a friend.

If the the solenoid connections show the correct voltages you have a defective starter/solenoid.

Bill Matheson

I appreciate the help!
I'll test the starter hot leads this weekend and let you know what I find.
The thing that has me confused is the instrument cluster not coming on. Normally, it illuminates so you can interface with the computer.
I get nothing in an key position.

Anker

Do you have a wiring diagram? I would definitely start with the ignition switch and move from there.

Bill Matheson

Yeah, that makes total sense.
Thanks!

Rudeney

12.4v is a little low. Does it drop even more when you turn the key to the start position?

Bill Matheson

Not sure. Haven't had a second person to turn the key while I watch the mutimeter.
I'll have a hand on Saturday.
I'll let you know.

Rudeney

Use the built-in voltmeter on the "hidden" MFD menu. Search "dyno mode" to find out how to enable it.

Bill Matheson

Wish I could.
I'm getting no power to the instrument cluster.
I can't interface with the cars onboard computer at all.

Bill Matheson

Hooked up the multimeter to watch the battery when I turn the key to start.
The car actually started!
Now, I still have no instruments or gauges, and the wipers don't work!
I'm thinking maybe a couple overlapping issues?
Or, could it still be a key switch issue?

Anker

What voltages did you see when cranking and when the engine was running? It could still be a battery voltage issue.

Bill Matheson

12.4 mean
10.1 cranking
14.4 running

Anker

Cranking voltage is on the low side, indicating a weak battery.

When you say mean, is that when the car is shut off? If it is, its also on the low side.

The running voltage is just right, indicating that the alternator and voltage regulator are working fine.

Personally I would remove the battery and take it to a battery shop and have it tested before doing any further diagnostics. When replacing the battery make sure everything is clean and tight. A post and terminal cleaner is a cheap investment.

Bill Matheson

Yeah, 12.4 resting, or shut off.
I will have it load tested.
It's probably a good idea just to get a new one.
We had an unusually cold winter. That probably didn't help.
Thanks for the response.
I'll let you know what happens.

Rudeney

This could be an issue with the EIS or the key. A key that won't properly "handshake" with the EIS can act like this, too. But first - fix the voltage issues - 12.6 at rest, no less than 11v during cranking.

Bill Matheson

Went ahead and bought a new battery. The old one was a bit week under load
New one installed, car starts right up, but still no gauges.
This time the wipers came on for a brief second to park themselves in the up position.
Things are getting weird!

Rudeney

Do you have a spare key and if so, does it do the same?

Bill Matheson

No spare key.
I might end up dropping it off at Mercedes.
I was hoping to avoid the huge dealer service rate.

Rudeney

You need a spare. Before spending any money on a service visit, I'd get a spare key. You need one anyhow, and it may be that your key is defective. Got to "parts" and get an "additional" key.

Bill Matheson

Do they have to sync it to the car?
Or, will it come synced based upon the cars serial number?

JimVonBaden

No, it works out of the box. I recently purchased one. $280. Took 3 days.