2L8ULUZ

Hi there....

Can you give me an example of what cable or quick fix item you used to connect the two points? It's not a matter of just jumping it like a car battery, but a continuous feed correct?

THX!!

Arrie

The engine goes to Limp Mode from low fuel rail pressure on the high pressure side. Either you have a pressure sensor problem or pressure really goes low meaning it is a pump problem. May also be low pressure pump issue if it does not supply enough flow to the high pressure pump but I don’t think this is likely.

For your dealer to see the problem you would need to drive it to them (or other MB service) without shutting it off so the faulty condition stays for them to see the error codes.

I used out-of-town dealer with my radio issues when my own dealer could not see the problem and got it diagnosed correctly this way.

But, if your car goes limping easily when flooring the pedal you can make appointment and before going to it drive and floor it so you can show it to them. Just remember not to turn it off.

juanmor40

Do you have a scanner for MB? Does it always happen, or only when the fuel tank is @1/2 or less? if the gauge is above 1/2 mark, there is always plenty of fuel on the passenger's side.

As Arrie mentioned, it could be related to low pressure in the fuel rail which can happen if your passenger side of the tank is empty despite the fuel gauge saying otherwise. When you floor it, I am sure the fuel will move backward in the tank, and if both sides are not leveled with the passenger's side nearly empty the fuel rail pressure may suddenly drop. Worth scanning and check both fuel floats are about the same (regulated level) and not <1% on the passenger's side.

I wasted a ton of time diagnosing a W211 in limp mode with 1/4+ fuel in the tank with the passenger's side basically empty ( I then scanned my W212 and both floats were identical). As Arrie mentioned, try getting the scan w/o turning the car off; otherwise, all the bets are off and start all over again.

My 2c

CaliBenzDriver

These cars loosing steering assist and engine power are never a pleasant surprise. Are you interested in immediate relief?

Here is my simple medicine :

1- CHARGE main battery overnight
2- Disconnect batteries to RESET computers
3- Drive with HEADLIGHTS:ON (13.5V trick!)

99% chance the 3 above steps will prevent your limp-mode and "XYZ Inoperative" warning messages - If you dislike batteries sparks then do the #3 step only.

It's NOT a tip for all limp-modes but in this case, it should make your car safer at intersections and highway speeds.

Txs for all updates with your observations.
​​🤞

2L8ULUZ

Can you please tell me what heavy cable you used to jump this?? Or suggestions as what type of cable to use? I'm going to store one in my trunk...LOL

THX!!

juanmor40

WARNING: Jumping between posts w/o a fuse may be looking for more trouble than you already have. Perhaps I am being paranoid, but if there is a short already and you jump it w/o fuse you are going to fry something downstream, ie.. $$$$

CaliBenzDriver

if it was me I'd use standard "jump starter" cables. They are thick enough to make any trouble spot start glowing red. A spare cloth hanger may get this going too....


Seriously, before jumping your Prefuse... you'd want to find out what caused it to quit.

You want to avoid situations where an unforseen load is placed across your 800CCA battery or alternator. It's not high voltage, yet it's high power. Given enough current every conductor can melt.

I once had a 5000A (five thousand Amperes) railway fuse in my hands wondering what it was! It is not as huge as the current implies, 2Lbs.

2L8ULUZ

I understand this, but I don't wanted to be stranded anywhere and at least be able to drive to a repair location vs dealing with a difficult 4matic tow.

Left Coast Geek

towtrucks deal with AWD cars all the time, they either put them on a flatbed, or they put the rear on a dolly, and lift the front (or visa versa). around here, nearly all towtrucks are flatbeds now, due to the prevalance of 4x4 SUVs and such. I watched one drag a Chevy Tahoe that had completely torn off a front wheel onto his truck the other day.

juanmor40

I hope you realize you are already in the hole if you get stranded with a damaged pre-fuse box, so you can play Russian Roulette with those posts and

1 - Get lucky and nothing goes wrong, but you still have to pay for the pre-fuse box (@$300 + labor) + whatever made it quit
2 - Less lucky and just fry the RearSam (@$500 + labor), plus (@300 + labor + whatever made it quit the first time) plus still the inconvenience of the 4matic tow
3 - A bit worse and something else (like other CU's) goes down, i.e. $$$
4 - Not so lucky, and it goes really wrong and you fired up a component that may burn some section of the car, $$$$

Please keep in mind the fuse is NOT the failure and the source of the inconvenience. A fuse is an engineered device to prevent more expensive damage downstream of the system, i.e. YOUR car (not ours), and allow diagnosing of the "original cause of the failure" (not the fuse) before replacing the fuse. If you feel very strongly that you need a fallback and the pre-fuse is very likely to fail you, buy a spare one and learn how to install it. Once the spare one (financial fuse) gets fried again, you can wait for the tow truck and keep the $$$ damage limited.

My 2c, and my best wishes when playing Russian roulette.

PS: Another MB owner telling a sad story of her attempt to jump-start a friend's car with her perfectly working W166. Not certain what went wrong, but her car ended up with a cluster lit like a Christmas tree, not started after that, and $3000+ in electrical components plus the unknown hidden damage that will likely unfold in the coming months. Very very sad to hear that one.

Left Coast Geek

indeed, I stopped carrying jumper cables, and got a NOCO Boost Plus 1000A lithium jump pack. takes less space than the cables, and means I can jump someone else without risking my car, OR I can jump my car without needing anyone else.

S-Prihadi

The left one, POST IG1, fuse 158 is a power source downstream of K2 relay.
It is protected by a 150 amps fuse. This power is called 30g, meaning it can be killed using the K2 Relay. This IG1 goes to REAR SAM N10/2.

The same K2 relay also feeds fuse 156 of also 150 amps , connection is named MRG2 or MG2. You cant see this connection until you remove F32 prefuse from its mounting point.
MRG2 / MG2 is for FRONT SAM.

Only the 2 above power cable are controlled by K2 relay. So they are called 30g circuit. Only has power or HOT if the K2 relay is activated.

===================================

Post/terminal IM1 is using fuse 159 of 200 amps and that goes among others, to parallel relay K114 at the side of AUX baby battery at the trunk and if fcar has a 9 speed tranny, it get power from IM1 too.
This is called Circuit 30, always HOT....always has power no matter what, as long as battery is not disconnected.


====================================

If you want to confirm that K2 relay is OK, you need to simply undo F32 pre-fuse and lift it up, remove a cover to expose MRG2 or MG2 and test if this one has power or not ?
If MRG2 or MG2 does not have power, it can also be it blown its 150 amps fuse...but most likely NOT.
If MRG2 or MG2 has +12V power.....you better DO NOT jump IG1 with bare wire un-fused as something bad has happened to be able to blow a 150 amps fuse F158.

What you can do is, get a 30 amps fuse, and then jump IG1 from that official jumper/charging positive post which is like a blade next to IM1 , please .... not from IM1.
Why 30 amps fuse ?
AA. Without engine running, a mere door opening is under 12 amps for a typical W212. All accesories/heater/HVAC...everything OFF yah. Do not play with power window too if you can avoid it.
BB. A ready to crank iginition at position 2 ( where dashboard all lights up) and Engine Computer active, approx 22 amps.

AA is low risk.
BB is high risk even if fused at 30 amps.


My F32, for my car



Read here to know more of F32 and Front SAM
https://mbworld.org/forums/e-class-w...-87m-50-a.html
Download my PDF file and the excel to understand better. The last pages of the PDF has information on F32.
It is edited specific for my car, but many similarity if your engine is M276 3.5L.

Good luck and becareful..........

DHUX78

what was the final diagnosis and fix?

CaliBenzDriver

A genuine battery