W221 S400/S550
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W221 S400/S550
Hi! A few months ago, I became the owner of an S400 Hybrid, which I'm not entirely proud of. I'm currently having quite a few problems with this engine, so I wanted to consider swapping it to a 5.5. Does anyone have wiring diagrams for both the 2011 S400 Hybrid and the pre-facelift S550? I have a wrecked S550 with all the necessary parts, but the engine harness and air conditioning need to be rebuilt, and I don't want to burn anything up.
thanks for every advice
thanks for every advice
Super Member
Joined: Jun 2025
Posts: 784
Likes: 248
From: USA
Hi! A few months ago, I became the owner of an S400 Hybrid, which I'm not entirely proud of. I'm currently having quite a few problems with this engine, so I wanted to consider swapping it to a 5.5. Does anyone have wiring diagrams for both the 2011 S400 Hybrid and the pre-facelift S550? I have a wrecked S550 with all the necessary parts, but the engine harness and air conditioning need to be rebuilt, and I don't want to burn anything up.
thanks for every advice
thanks for every advice
MBWorld Fanatic!
Joined: Aug 2023
Posts: 3,687
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From: MA Coast
W204 2010 C300 4matic Sport M272
Can find diagrams here: https://charm.li/Mercedes%20Benz/201...ment/Diagrams/
Not sure how complete they are. Will have to do alot of digging around.
Not sure how complete they are. Will have to do alot of digging around.
Super Member
Joined: Dec 2015
Posts: 502
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From: Tampa Bay, FL
2014 E350 Wagon, 2009 SL550 no ABC
Sorry to hear that you have bought S400. But it can be fixed, Problems are typically not with the engine (V6) but with the hybrid nonsense. So you can throw out the hybrid portion and just drive on the gasoline engine alone (been there and done that). But parts and labor for that would be around $8000 if you have someone else do it. If you swap the engine to V8 it will be a major work as well. Unless you are an expert in Mercedes electronics and CAN sniffing and can do the electronics yourself (mechanical parts are relatively easy) I would forget it.
My recommendation would be to just junk the car/sell it/sell it for parts and buy yourself S550, which will be infinitely cheaper and easier than working with the S400
My recommendation would be to just junk the car/sell it/sell it for parts and buy yourself S550, which will be infinitely cheaper and easier than working with the S400
Super Member
Joined: Dec 2015
Posts: 502
Likes: 145
From: Tampa Bay, FL
2014 E350 Wagon, 2009 SL550 no ABC
Remember that in Mercedes everything is connected and major parts are programmed "for your protection" to only work in your specific car. So you will need to reprogram everything, COMMAND system etc. Dealer will not help you here because such conversions are above their skill levels. You are on your own. Just get rid of the S400 and move on.
Last edited by George993; Oct 18, 2025 at 09:02 AM.
Super Member
Joined: Oct 2023
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W221 S500
The issue won't be making the M273 work, but rather making the hybrid disappear.
Unless you're talking literally making an S500...
Not to be controversial, but that's probably doable as long as the hybrid unit and gearbox can take the V8 torque. To make the engine work, the body harness will be fine but you need to swap the V8 and it's loom. The engine ECU might be possible to reconfigure to the V8 which will save you a lot of messing around... The M273 is basically an M272 with two extra cylinders. So electrically speaking it should be plug and play as the ECU to engine wiring is what controls the ignition and fueling.
If you can't reconfigure the engine ECU, then the work is going to treble.
The S500 donor needs to be stop start enabled as a bare minimum because the S400 gearbox is and stop start adds a TC pump so the non stop start conductor plate won't work. From a security point of view you need the following to match.
EIS
ISM
Conductor plate
Engine ECU
Remote central locking module
Keys
If you can get away the S400 trans and engine ECU then you have a chance. If not, then trade it out.
Unless you're talking literally making an S500...
Not to be controversial, but that's probably doable as long as the hybrid unit and gearbox can take the V8 torque. To make the engine work, the body harness will be fine but you need to swap the V8 and it's loom. The engine ECU might be possible to reconfigure to the V8 which will save you a lot of messing around... The M273 is basically an M272 with two extra cylinders. So electrically speaking it should be plug and play as the ECU to engine wiring is what controls the ignition and fueling.
If you can't reconfigure the engine ECU, then the work is going to treble.
The S500 donor needs to be stop start enabled as a bare minimum because the S400 gearbox is and stop start adds a TC pump so the non stop start conductor plate won't work. From a security point of view you need the following to match.
EIS
ISM
Conductor plate
Engine ECU
Remote central locking module
Keys
If you can get away the S400 trans and engine ECU then you have a chance. If not, then trade it out.
Last edited by AL5461; Oct 18, 2025 at 09:26 AM.
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