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Fuel pump relay not being activated by control unit
I have a crank, but no start condition. I can activate the fuel pump using the DAS activations but it will not activate on normal startup. I had a few
fault codes including the Rollbar and Alarm siren codes. I fixed the Rollbar code. I can't activate the alarm siren with DAS, probably something wrong with it, but I went ahead and coded the PSE control unit to no ATA system, no alarm system, which got rid of the siren alarm code which I thought might be preventing the car from starting. I now have 0 fault codes but I'm still not getting 12vdc from the ME-SFI control unit to activate the fuel pump relay. I do get the 12vdc when activating it with DAS. Any idea's????????????
I did try and test the CPS with DAS but it required a socket box and another test set.
This is the part that concerns me. The ECU shows the status of drive authorization as "immobilizer is activated" but it
also shows the immobilizer as "not active". I checked the EIS control unit (the ignition) and it shows everything happy. It
see's the key and data being transmitted and all looks good.
I tried jumping across the fuel pump relay to activate the fuel pump, but the car still would not start. I suppose the ignition coil is
also disabled. I will throw a CPS at it.
I did try and test the CPS with DAS but it required a socket box and another test set.
This is the part that concerns me. The ECU shows the status of drive authorization as "immobilizer is activated" but it
also shows the immobilizer as "not active". I checked the EIS control unit (the ignition) and it shows everything happy. It
see's the key and data being transmitted and all looks good.
I tried jumping across the fuel pump relay to activate the fuel pump, but the car still would not start. I suppose the ignition coil is
also disabled. I will throw a CPS at it.
Mark
Those socket boxes can be very expensive.......the one required to probe the soft top N52 controller is around $2,700 MRSP!
The ECU uses the CPS signal to control the fuel and spark delivery.
I can suggest other methods to see if it's generating a pulse train when the engine cranks, but it requires removing the CPS connector and probing the CPS terminals with a multi-meter, as the engine cranks. You also need to know if the CPS uses magnetic or Hall effect technology (I believe MB uses the later). However, it's easier to just replace the CPS.
IMHO, given the number of forum CPS failure threads, it's a wear and tear item, which probably should be replaced as preventive maintenance.
My CPS bit the dust 5 years ago at around 80,000 miles (e.g. difficulty restarting a warm engine and engine shut downs when stopped at traffic lights).
A Bosch OEM CPS runs around $35 and an easy DIY replacement (took me less than 10 minutes on a M112 engine). The only PITA was access to the CPS on the bell housing. I found using a 1/4" ratchet wrench with a very long extension and E8 torx socket worked well. The socket wasn't magnetized, so I added some bearing grease to prevent loosing the fastening screw. Also, during production, the W208 used 2 different CPS types (e.g. difference being that there were either 1 or 2 locking tabs to squeeze to remove the connector). My CPS pulled right out (sometimes they stick and require more effort).
New Bosch CPS installed, no change, good crank but no start. I checked for spark and I do have it at the spark plug. Fuel pump should come on momentarily when I turn the key to on, but I still don't even get that. I can operate the fuel pump with my DAS computer. There is a youtube video of a guy going thru the drive authorization settings with DAS and mine are the same as his, so I don't think it has anything to do with that. Again, I have no codes and everything looks good. Unless someone has another suggestion, I think my only other option is to replace the ECU.
Mark......to clone your ECU, using a donor ECU, means that you'll have to know what chip to extract from the donor and replace in your ECU. It's a pretty tricky and delicate operation as shown in this video, where the fairly easy immobilizer chip (e.g. with few connections), was extracted and replaced.
Here's another video, of a no start on a MB 2004 E500. It's 55 minutes long, not exactly your symptoms but worth watching, because the fault was no communication to the ECU, which was caused by it not getting power. The culprit was a faulty fuse in the N7-1, combination Fuse/SAM, (signal pickup and actuation) module. Turns out the fuse was not making a good electrical connection when inserted into the socket, due to corrosion.
Given that the ECU in our W208's s located in and powered by the N10/1 Fuse/SAM, could the issue be similar (e.g. ECU not being powered by the always present circuit 30 or switched circuit 87 voltage supply or ground) and why you were not able to pull any ECU DTCs?
Here are a few other possibilities.
I've enclosed some additional information that explains how DAS3 (drive authorization system) works and interior . Note that the ECU doesn't release the engine to start until after the 'ignition on' authentication check is made between the ECU and the EIS N73 fob. Also the N73 is a node on the interior CanBus. Have you tried your spare fob or checked for N73 communication DTCs?
Since you have been able to override the fuel pump operation, but still without starting the engine, I've also enclosed a diagram of the fuel supply system. Could a malfunctioning actuator, solenoid valve or pressure sensor be preventing the fuel pump from operating normally and/or preventing ample fuel delivery to the injectors?
Last edited by Serndipity; 06-25-2018 at 05:25 PM.
Since you have been able to override the fuel pump operation, but still without starting the engine, I've also enclosed a diagram of the fuel supply system. Could a malfunctioning actuator, solenoid valve or pressure sensor be preventing the fuel pump from operating normally and/or preventing ample fuel delivery to the injectors?
This is more the direction I'm heading. After checking for spark and getting it good, the car should have started after bypassing the fuel relay. Yesterday, I checked the fuel at the fuel rail and got nothing when
the fuel pump was running. So I either have two problems or something in the fuel system is causing the ECU not to power the pump, as you say maybe an actuator or solenoid. (although I think I would get a code if that were the case)
Tonight I'll check that fuel is actual coming from the fuel tank to the pump and go from there.
Looks like I have at least a bad fuel pump. I can hear it running but there's no gas coming out of it. Hopefully when I replace it, I can get it running and the ECU will give me a code.
Installed a new fuel pump, bypassed fuel pump relay to pressurize the fuel rail. Car started and ran just great. Turned off ignition, replaced pump relay, Turned on ignition and now I can hear the fuel pump run for a second and shut off, as it should. Started the car and it runs fine now.
I dunno, I suppose the ECU somehow reset with signals from a running engine.
Well, I was fully prepared to clone the ECU. From my research, it looks like a KESS V2 V5.017 software version v2.23 or higher would have done the trick. About $100 on ebay.
Well, it happen again. This time had to get the car towed home. Crank but no start. Same deal, no voltage at the fuel pump relay from the ECU.
I bought a KTAG ecu programmer from ebay for $85 and a used ecu for $25. Great thing about the KTAG unit is you don't need to desolder any chips
to read or program them. Able to copy the data from the 3 chips on the original ecu no problem. When writing to the used ecu I kept getting a write error
to the EEPROM chip. The other two chips were fine so I figured it was just a bad ECU. Ordered another used ECU from ebay and all 3 files wrote
correctly on it. Put it in the car and it fired right up with no problem!!!!! Saved a ton of money and the wife is off my back!!
I'll start a new thread with a video on how to do it.
Well, it happen again. This time had to get the car towed home. Crank but no start. Same deal, no voltage at the fuel pump relay from the ECU.
I bought a KTAG ecu programmer from ebay for $85 and a used ecu for $25. Great thing about the KTAG unit is you don't need to desolder any chips
to read or program them. Able to copy the data from the 3 chips on the original ecu no problem. When writing to the used ecu I kept getting a write error
to the EEPROM chip. The other two chips were fine so I figured it was just a bad ECU. Ordered another used ECU from ebay and all 3 files wrote
correctly on it. Put it in the car and it fired right up with no problem!!!!! Saved a ton of money and the wife is off my back!!
I'll start a new thread with a video on how to do it.
i got these same issues on a 2016 C63S, replaced fuel pump twice and after week or two does same thing. Kicks over but won’t start, not throwing any codes but just won’t start. Was it main ECU you replaced ?
Yes it was the main ECU under the hood. Make sure you are getting the proper signal to energize your fuel pump relay. If not, then I would suspect the ECU or an input signal to the ECU (like the crankshaft position sensor). If you are getting a good signal to the fuel pump relay, then bypass the fuel pump relay and see if it will run.
got the scan tool and worked a treat, it actually found and cleared more codes than the star unit guy has been using from merc. Will update you all if car goes well for next week or two as that’s jdhdlky around time it has issues. Other thing found was main battery was too small so need to replace that.
06-16-2018, 02:25 PM
