Hello. i am currently having an issue with the red battery "visit workshop" warning. 2003 e500 w211. batteries are good, alternator is good, fuses are good. But here is the thing, i needed to replace my fuel sending unit and afterwards is when the issue started and has not gone away at all. car is functioning fine and voltages are 12.7 at rest on both batteries.

im thinking that there is a possible parasitic drain from the new sending unit and its triggereing the warning. i only have obd2 and dont want to pay 265$ just for MB to hook it to star and tell me the exact codes for it.
please help.
how would i be able to test for partatistic pump stealing electrons from my batteries?
do i need a new sending unit?
why did it happen right after replacing my fuel pump?

 

Not sure what you mean you only have obd2. If you dont have a Mercedes specific obd scanner then I would get one, cheaper than one visit to the dealer.

Could be just coincidence the battery warning started after replacing the fuel pump.

How did you test the battery and the alternator?

I would scan for codes.

 

I came across some testing procedures to see if things are shutting off. Still says to read and erase codes as one of the steps.

Heres a link: https://charm.li/Mercedes%20Benz/200...20Consumption/

 

MB STAR requires a yearly license and im not going to use a bootleg diagnostic tool. batteries and alternator were tested using a multimeter manually with and without load. the fuel pump wasnt oem and the fuel guage stopped working a few days after install but visit workshop started as soon as i reconnected the battery after doing the fuel sending pump unit and has not gone away at all since. im thinking the cheap amazon product is throwing the wrong volts and the wiring harness is freaking out about it. new fuel unit on order ill update after i swap it in.

 

UPDATE. I REPLACED THE FUEL SENDING UNIT AGAIN. IT DID NO RESOLVE THE ISSUE. mb WANTS $265 FOR JUST DIAGNOSTIC...I THINK IF I CAN GET A NEW BCM AND AUX BAT RELAY FOR THAT MUCH LMAO SHOULD I JUST REPLACE THOSE PARTS AND HOPE THAT WAS IT?

 

Go buy a new YTX14-BS AGM battery (motorcycle / powersports) and change out the aux battery under the hood.
You can buy online for under $50.
Don't continue your argument that you "tested" it already and got 12.7 volts.