I HAVE A 2004 CLK500 WHITE EXTERIOR/ BLACK INTERIOR WITH 169,705 MILES ON IT.
OK HERE'S THE STORY: I PULLED IN BP GAS STATION TO PUT AIR IN TIRE(LEFT CAR RUNNING,HOPPED OUT) OUT AIR IN TIRE THEN HOPPED BACK IN CAR. I PUT CAR IN REVERSE , IT DOESN'T MOVE THEN WHEN I TRY TO PUSH BRAKE ALL TE WAY DOWN IT DOESN'T GO DOW ITS STUCK. I TURN CAR OFF TRY TO TURN IT BACK ON IT JUST CLICKS.( I HAVE HAD PREVIOUS DEAD BATTERY ISSUES BUT RULED THAT OUT BECAUSE CAR WAS RUNNING WHEN I JUMPED BACK IN IT BUT I DO NEED TO REPLACE IT SOON BECAUSE THE GUY AT AUTO-ZONE TOLD ME I HAD A FORD CAR BATTERY WHICH WAS AN EVERSTART WALMART BATTER SMH). ALSO AFTER WAITING 5 MINUTES I TRY TO START THE CAR AND IT STARTS BUT DIES 4 SECONDS LATER I GOOGLE WHAT IM EXPERIENCING THEY SAY FUEL PUMP. LUCKILY THE BP GAS STATION I WAS AT HAD AN AUTO REPAIR CENTER ATTACHED TO IT SO I HAD THEM LOOK AT IT THEY SAID IT WAS THE FUEL PUMP. NOW THEY SAID I CAN GO 2 WAYS I CAN BUY AN AFTERMARKET BATTERY WHICH I CAN HAVE THE SAME PROBLEM IN 6 MONTHS TO A YEAR OR I CAN GET AN OEM FUEL PUMP AN SOLVE THE ISSUE.

I HAVE FOUND
Spectra Premium Fuel Pump Part Number: B5065M $222
CARTER P76560M {#2094700194} Module Assembly$220
AIRTEX E8531M Module Assembly; Includes Pump, Sending Unit, Float, Reservoir, Strainer & Tank Seal$167
I FOUND ALL THESE ON ROCKAUTO.COM
BUT AUTOZONE GIVES YOU LIMITED LIFETIME WARRANTY FOR THE SPECTRA FOR $309
I AM LEADING TOWARDS THE SPECTRA BUT IS IT AN OEM OR AFTERMARKET

BUT I FOUND ON EBAY A USED OEM Mercedes 209 CLK500 Fuel Pump Main Sender 2094700194 Oem $87 iS IT SMART TO BUY A USED PUMP
SO I WANT TO KNOW WHICH WOULD BE THE BEST FOR ME TO GO WITH I WILL PURCHASE THE FUEL PUMP IN 7 DAYS ON JUNE 4TH SO THANKS 4 THE HELP.
PLUS THE LABOR FOR 2HRS FROM THE BP MECHANICS IS $250. DO YOU RECOMMEND A DIY OR IS IT TOO RISKY SINCE WERE DEALING WITH GAS I DONT MIND TO PAY 4 LABOR RATHER BE SAFE THAN SORRY.

ASLO IM KINDA OF WORRIED AFTER READING OTHER POST READING ABOUT SAM ISSUES OR CPS. ANY ADVISE IS HELPFUL

 

If you love the car Bite the bullet and get a garage to do it all, If you have time a patience and good skills DIY. Personally if it was me I would get a garage to do it all Ive have my fuel pump reconditioned already.

 

Unless I am reading this wrong, you are taking the diagnostic advice of a place that said you could buy a new battery to cure a fuel pump issue for 6 months to a year? That is no advice at all. You may need a fuel pump, but advice from those guys is zero evidence of that. I'd be thrilled if it were a CPS instead of a fuel pump. Way cheaper and way easier. Do not let gas station mechanics work on our car. You should take it to an indy mechanic that works on mercedes and has mercedes STAR system and get it diagnosed properly. Then decide if you do the work yourself.

 

First of all, welcome to the forum! You might consider not typing in all caps - it's generally considered yelling and is harder to read. If you have a disability that makes it hard to type, then consider just using all lower case letters.

I'll +1 Yidney's post (as I usually do - he's a smart guy!). And I'll add some of my thoughts:

Is it possible the engine had died as you shifted to reverse and you did not realize it? The brake pedal should operate regardless of the engine running or not, but with the engine stopped, it gets no vacuum boost and thus would make the pedal feel very firm, like it won't move at all.

This is most likely a dead or weak battery. It's easy enough to check this for yourself with a simple voltmeter or the on-board voltmeter (search The Internet for "mercedes dyno mode" to find how to access the hidden menu on the instrument cluster that includes a voltage display). You should have at least 12.6v at rest (all consumer off, doors closed), 11v during cranking, and 14v at idle. There is nothing special about your car's battery, it's just a 12v automotive unit. However, because your car is a "network of computers on wheels", it has high electrical demands so you need a battery of the proper amperage capacity to keep all this powered. It requires 825 CCAs and uses an H8 group size. I like the Advance Auto Platinum battery - it's an AGM style so it charges more quickly, drains more slowly, and lasts longer.

While this could be a bad fuel pump, there is nothing the definitely points to that. Voltage problems can cause all sorts of issues with the car's electrical systems, including no-start, dying, or strange messages and behaviors. Also, let's make the distinction about "cranking" vs. "starting". Cranking is the rotation of the engine by the starter motor. if this does not occur, then it's either a bad battery, bad starter, fuse, relay or a serious problem with the ignition switch or other vehicle electronics. This would have nothing to do with the fuel pump. Starting is when the engine cranks and then begins running. A failure to start could be a problem with fuel delivery, bad CPS (crankshaft position sensor), or serious electronics issue (like a bad ECU). If the engine does start and runs and then dies, pretty much the same culprits as a no-start.

It is easy enough to check operation of the fuel pump with the proper tools and skills. There is a Schrader valve on the fuel rail where you can check pressure and also you can check the current draw on it's electrical connection:

http://benzbits.com/w209/FuelPressureTest.pdf
http://benzbits.com/w209/FuelPumpAmpTest.pdf

One very common cause of a no-start or engine dying is a bad CPS. This reports to the ECU that the engine is running and it's relative angle by magnetically sensing a pulse ring on the flywheel. When the ECU fails to get a valid signal from the CPS, it assumes the engine is not running so as a safety feature, it shuts off the fuel supply. Note that the fuel pump will still pressurize the system upon turning the key to the "run" position so amperage and pressure can still be checked. CPS failure often occurs at extreme temperatures. If it's heat, you can sometimes temporarily fix it by pouring cold water on it. It is located on the back of the engine, on the bell housing, on the left (USA driver's) side.

Now, with all this in mind, I'd start first with the battery. Get is checked and replaced if it is bad. After that, if you still have issues, go for a proper fuel pump diagnosis. If that checks out, then you may need a new CPS. If so, get a quality one - MBZ or Bosch from a REPUTABLE supplier (not ebay/Amazon).