Okay, vehicle died on the freeway the other morning. Went and got an OBDII reader, and got code P0335 which is CPS. I changed that, no luck. Tow it to the house, and I can hear the fuel pump is not kicking on. fuse is good, relay is good, pump comes on with jumper, there is also about 8 volts on the energizer circuit and 12 volts on the the contact circuit. no voltage at the pump. Nothing apparently wrong with the SAM, everything else that it controls functions properly, i disconnected all of the connectors and everything looked very remarkable, actually...no signs of damage. I just bought this vehicle, and I am not very familiar with Mercedes.. The battery seemed kind of weak, so I went and bought another one, also bought new batteries for the key. What are my next steps?

 

A Crank. Position Sensor code will shut down the fuel delivery. Did you clear the code after the repair?

What fuse did you check, fuse # and where?

 

no, i actually did not clear the code... i didn't even think about it, i just figured the ECU would check for a signal the next time the key was cranked...wrong assumption? lol.
I did check the fuse, it's a 20 amp just right next to the relay, i've swapped the relay with horn relay, and that checks out good. I guess I'm gonna go borrow the obd2 reader again and clear the code to see if it starts... if that's all it is, i'll be rather let down about all i've done trying to chase this down...but relieved all at the same time... thank you!

 

I asked you a specific question, "What fuse did you check, fuse # and where?" and you didn't answer. How could you miss the question?

 

clearing the code didn't change anything.

 

i didn't miss the question, just didn't have the information... it's #57 in the fuse box next to the rear SAM.

 

I've actually checked every fuse in the fuse/relay box under hood, the rear fuse/relay box, and the fuse box on passenger side in dash... everything looks good.

 

1. what does this mean......there is also about 8 volts on the energizer circuit and 12 volts on the the contact circuit? Do you mean that there is 8 v on circuit 15 and 12v on cir. 30?

2. did you check to see if code P0335 is still stored?

3. Does the eng. crank when turning the key or nothing at all?

4. did you check to see if the connector is snapped in on the CKP Sensor?

5. also check fuse 51 in the cargo area fuse box.

6. is the relay you checked KO in the rear fuse box?

 

1) i don't know what circuit 15 and circuit 30 are... if you could explain to me which pins of the relay to test to measure voltages, I will. I've taken measurements, but if they don't make sense to you, they probably aren't the right ones..

2) p0335 is cleared. It also had other codes related to the fuel circuits, i cleared those, and figured they had occurred due to all of my plugging and unplugging for testing.

3) the engine cranks just fine, will start with a little gas put in the throttle body, and after i jumped relay "O" across pins 3 and 5, fuel pump kicked on, and i was able to start vehicle with pressure after i removed jumper, but still wouldn't remain running.

4) the connector is in as far in as it will go on CPS (i would like to check the other end of the connection to where the CPS sends it's signal to check for continuity/signal, but I do not know where it goes)

5) 51 fuse is good.

6) i'm not sure what relay "KO" is... I have relay "K" which is for power seats and relay "O" is for the fuel pump. relay "O" is identical to the horn relay in the front compartment, i swapped to verify relay is functioning.

 

after completely removing the rear SAM, there is water underneath it, and after removing the cover, there is some type of residue... nothing looks burnt or damaged, going to clean and put back together and see what happens.

 

still doesn't work... i just don't believe it's the rear SAM because nothing else is malfunctioning that it interfaces with. I would like to know about the voltage on pin 2 of the "O" relay... why is it ~8v dc instead of 12v dc (with key turned to position 2)? is it supposed to be?

 

Maxwell, you have found your problem. Rain water entry due to faulty tail lamp seals. This must be addressed first to stop future water entry. When you remove the lamps you will see that the seals are attached to the lamp instead of the body opening.

Did the residue look like this video? If so, the SAM must be completely disassembled towers included and cleaned with toothbrush & electronic contact cleaner.

 

Post your full vin# for diagram purposes.

Here is the location of the KO relay.

 

What were the other codes that you erased? Very important.

It is impossible that there are no codes stored in the 25 or so modules in your vehicle. If you are just using a cheap code reader, it is useless.

You must have a scanner that will scan the entire veh. They even have codes for the fuel system.

 

vin# 4JGBB86E56A053506 ...KO relay is the one that i've been working with... i went to bypass it again, and the pump wouldn't come on, so i took the mallet to it and it kicked on. also, there was some voltage at the leads for the fuel pump this morning when cycling the key... but it's only 2 or 3v dc vs 12v if i jump the KO relay across 3 and 5 pins.. i should clarify, i got an 8v reading across pins 1 and 2... but i've realized pin 1 has 12 v on it, and pin 2 has 3.5 volts... it almost seems that whatever is sending that 3.5 volts, is what is not letting the pump kick on since a 9 volt battery across pins 1 and 2 closes the relay... i'm guessing the 3.5 v is coming from the SAM, but I would think that it would receive a signal from the ECU telling it to send it? schematics would help...lol

 

it not an MB STAR, but it was $250 buck deposit to borrow it from the parts store... it had picked up fuel system codes, but as i said previously, i cleared all the codes because you told me the p0335 code would not allow the vehicle to star, and i was so excited that it was something stupid silly that i overlooked, i didn't bother paying attention to the other codes, I just cleared them.. they weren't there when the vehicle initially broke down, just after i had got it home and started testing the fuel pump..

 

I thought we had some understanding that everything would be addressed.

You just supplied your vin# but completely ignored the rest. If you do not have a scanner everything will be guesswork.

 

the board for the SAM didn't look nearly that bad, but i'll take it out again and do a more thourough cleaning job...by towers i'm guessing those are plug recepticals? i did not take those off last night... so maybe my issue is under them..

 

i did not ignore the rest! i addressed your questions from that post with answers! I have replied to your other questions with the best answers i could give... man, i'm trying to be as detailed as possible with the information that I am giving you, and also reply in a timely manner... i don't know why you keep coming back to this "you didn't tell me what i asked" nonsense... if you need another piece of information, just ask and i will gladly give it to you.... it's just like with when you asked me which relay and fuse and i told you the fuel pump relay and the 20amp fuse right next to it, but that wasn't good enough... but it's funny you send me a picture of a fuse box, pointing to the SAME relay i was talking (that we've collabed and identified as "KO") about that has ONE 20 amp fuse right by it, also for the fuel pump... sorry i didn't have the designations, i wasn't at the fuse box, or a diagram, but i thought my description would be sufficient to tell you what i was looking at... i'm under enough stress already and i came here for help, and i figured by answering all these questions you've asked, you'd be able to help provide some new information (like the voltages, and the sources, or a schematic, which you said could be posted with using vin, which i provided and got this response instead of the schematic).... hopefully i have found my problem, as you say... but i'd feel more confident in your answer that the SAM is the issue if you could explain to me how it operates the relay, what wire to look at, and what voltage it carries (for fuel pump on and fuel pump off)... i'd also like to know what pin the SAM receives the signal from the ECU from, and what the "ON" signal looks like vs the "OFF" signal... so i can test if it's the SAM or the ECU... because if the SAM isn't getting the correct signal from the ECU, it's not going to matter if i buy a pure gold SAM from MBZ for $200k, it still isn't going to close the relay. I know if I could take get it on a STAR, it would tell me more, but I really don't have that option... it's not guess work... if the SAM is getting the signal from the ECU, it's the SAM. if the SAM is not getting the correct signal from the ECU, no matter if the SAM is good or bad, the fuel pump is not going to come one, and I really don't want to start throwing modules at it until I know which module is actually the problem...

 

*update* GOOD NEWS recleaning the rear SAM fixed the issue with voltage to the pump... after installation, it kicked the pump on and started right up.. BAD NEWS... my fuel pump is all but dead.... car died after a few minutes, i assumed it was the SAM again, but i checked and was getting voltage at the pump while cranking... and then after putting constant power to pump, I realized it needed some mallet motivation to get started :/ even then, the connection on the top of the pump just had to be touched for it to shut off, and it wouldn't re-engage without some more motivation..

this car had been repoed back in october and has pretty much set up until i purchased it... it had an empty tank, (i guess they didn't have money for gas neither..lol) and i'm sure that didn't help it... i would have ordered a pump a week ago, but said i wasn't going to buy the pump until i was sure that it was the pump, and up until today, it hadn't been the pump... gonna go ahead and replace the filter and sending unit on the driver's side of the tank while i'm at it, and hopefully that will be it for awhile.

i'll post another update with the pump arrives and is installed.

 

And you thought that because everything else was working in the SAM, it couldn't be the SAM.

What are you striking with a mallet and exactly where?

 

On the top of the fuel pump, I've removed the cabin cover on the passengers side floor panel.. at first it just needed a slight bump anywhere, but it got progressively worse rather quickly and required more and harder taps, closer to center on the pump... the pump has gone quiet and it won't work hard enough to build pressure at the rail... actually the last time I had it on, I thought that it had turned off, but it was just so quiet I couldn't hear it from th e front seat

 

I guess it's time for a new fuel pump.

 

yeah... would have been nice if the fuel pump circuit control circuit would have had integrity, and also for the car to indicate fuel issues instead of CPS... i mean, does it not seem strange for CPS, rear SAM, and fuel pump to all give up at the same?

another note on the cabin covers for the tank... all the other ones i've seen on every ML online appear to have a little adhesive under the lid.. mine, on the other hand, (and it appears it was done this way before factory paint) was cemented to the floor pan both under and over with a good 1/2 inch of adhesive...i don't know if the assembler thought they were doing someone a favor by going that extra mile... but i had to punch out the covers probably could have cut them out, but i didn't want to do something like cut through the top of the tank or a fuel line or wiring..

 

Then disassemble the rear SAM again and see if everything is clean.