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Hi guys. First time posting on here so I apologize if I leave out helpful information. Anyways I recently picked up a 2004 c240 hatchback. Guy said he replaced fuel pump and then 3 months later it went out again. When I turn the key to on I don’t hear it prime. Took off the back seat and unscrewed the fuel pump cover so I could access the plug. Checked the red and black wires going into the fuel pump with a multimeter and got 0 volts when moving the key from off to on. So then I went to the fuel sending unit side. Checked for 12v on the plug on the top of the sending unit. Getting 0 volts out of the thicker green/black wire no matter the key position. So then I traced the wire to the rear Sam. I can hear my fuel pump relay click when I turn the key to ON. but when I try to jump the relay I’m still getting 0 volts out of the green/black wire that comes out of connector 1 of the rear Sam to the fuel sending unit. I have 12v at the fuel pump fuse also. I am at a loss here of what could be wrong. Bad SAM? Maybe a bad ground going to the sam? I’m getting 12v from the big red wire to the rear sam along with every other thing the rear sam controls is working fine. Any help is appreciated! Thanks!
I had the exact same car for years and years and years. C240 (Wagon) 4Matic. Had almost 300k mi on the car when I gave it away.
But, I had installed two rear SAM in my ownership time. Both were purchased on eBay with good results (the one lasted about 80k before the third). That said, the new "old" SAM's are all getting up there in age and your results may vary.
Hi the wires in the 2nd picture that look burnt is just the black sticky tape that’s dirty. I’m thinking it’s the rear Sam because I have power to the relay. Power to the fuse. But no power out of connector 1 green/black wire to fuel sending unit. But I’m not to sure if it could be anything else
Originally Posted by Plutoe
what are all those that look like burnt wires at the top of pic 2----also if you dont have a scan tool, you have to have a wiring diagram to sort out all the connections but even at that how will you determine SAM microprocessor faults??
FYI red in is power in
hi thank you for responding. I haven’t read much about the CANBUS. Is this something I can check for a blown fuse or cut wire or bad ground? I this related to the “15r” circuit or whatever the fuel system is apart of? Thanks!
Originally Posted by Plutoe
the rear SAM has its own microprocessor to switch voltages based on the CAN instructions----you and me dont have the tools to determine a faulty microprocessor--its voltage in and assuming the key is in the correct position the rear SAM gets a message to apply voltage to the fuel pump and if the microprocessor is faulty it gets the message but cant comply---why---WTFK get a new rear SAM,but remember the rear SAM must be variant coded unless you know the part number and purchase the exact part number-----all others is a FUYA and must be coded
hi thank you for the reply sir. I ended trying to get a Sam from the junkyard. It solved the fuel pump issue. But then gave me about 14 different light errors on the dash. So I took it back and tried another. Fought the trunk for around 4 hours. Finally it. Exact same part numbers as the original. Fuel pump working great. Only issues are the trunk won’t open. Right side doors won’t unlock/lock. Fuel gauge not working. And the left and top brake lights are on all the time. I’m assuming all compatibility issues? Say if I found someone that can copy the info off my old Sam and put it on the new one. Would it copy the “bad info” of the fuel pump working or no. Thank you for all the help
Originally Posted by Plutoe
Post 6--No its not---see post 5 for what you have to replace
Hello Moto, I work for MBUSA and would like to help you if you are still struggling with making the "new" Rear Sam functional. The bad fuel pump info you are referring to is a wiring issue not a coding.
Each module is coded for the vehicle via the Developmental data screen in SDS. You do not need to worry about not being able to correct or change the "info". By knowing what options are listed under your vehicles VIN we can change the wrong options to the right ones under the developmental data menu in the rear sam module.
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