Hi all, I have a 2018 C350e that won't start. The dealership ran the diagnostics and came back with a faulty PECU (which I assume is another term for the hybrid inverter?). They quoted $15,000 to replace it, which is obviously more than the car is worth. Part of the problem seems to be that I'm in TX, way outside the car's original target market (California and the UK?), and nobody has seen one of these or is willing to try to fix it. I understand that it requires a lot of specialized equipment to install and program a new hybrid inverter and that sort of explains the high quote. So out of desperation I'm wondering if it's possible to make this car run gas-only. I'm willing to spend some money converting it as right now I'm looking at a total loss. Thank you in advance for any help or information.

You probably mean PCU (Power Control Unit). That's the brain of the hybrid system. It manages how and where the electric current flows, so yes, without it the car is dead in the water. Converting a PHEV/Hybrid to gas only is generally not feasible or recommended as the hybrid part is integral to the powertrain. Remember, the electric motor in the transmission is also what is used to start the engine. There's no longer a traditional starter motor. So if the hybrid side is dead, nothing is there to crank the engine. I suppose you could rip out the whole guts, transmission and all and replace it with the powertrain of a standard 350, but I doubt that'll be less than $15k. Anything is possible with enough money.

The cost of these repairs is so high, because nobody really fixes these modules. They replace them. It reminds me of a video I posted a while back where the hybrid system failed in a BMW. In that case the car was still running, but the battery wasn't charging anymore. The BMW dealership identified the failing modules and also wanted to replace them at a cost even higher than your quote. The video was from a shop in Germany, who was willing to open up one of the modules and found that a fuse was blown. The fuse is not meant to be replaceable, but they managed to source it and fixed the module. They did end up having to fully replace a second module, but the total costs was a fraction of what the dealership was asking. Unfortunately, the kind of shops that are willing to open up these modules and bring out the soldering iron to fix them are rare. Car mechanics aren't electrical engineers. Doesn't matter if you are in Texas or elsewhere. I'm curious, given that it's difficult to find a shop who could fix your PCU, what makes you think you'd find a shop who could do the conversion? There's a lot that would have to happen for the powertrain to effectively bypass the hybrid side. You'd need somebody who is intimately familiar with it, and if you find somebody like that, they could probably also just fix the PCU for less money.

@superswiss thank you for your reply!


The part can be bought relatively cheaply ($1-2k, if I'm looking at the right thing anyway, 205-900-10-36-64 or A2059001036 depending on the source; your comment about the name has me wondering if I'm wrong). The $15k quote was to replace it, not repair it. I was told the extra expense is because the unit has to be programmed to the car, which requires a) a technician with the proper high voltage certifications and b) usage of proprietary Mercedes technology to do the programming. I've gone to multiple independent shops, including two in town that specialize in MB and both declined to even look at it, citing those two reasons.

That's just my own ignorance, I'm grasping at straws to try and get this thing running again. It's a really nice car, all things considered. I figured since you can run it using either gas or electric then a failure of the hybrid system shouldn't preclude it running as a gas car.

In principal, one would think so, however the PCU also controls when the engine has to kick in and as said, the electric motor in the transmission is what cranks the engine to start it. If all that falls away, nothing can start your engine anymore.

Well... ummm, since you're at a standstill right now - how about cracking open said failed module to see if there's anything inside that can be easily replaced. For example a fuse, capacitors, diodes, etc. Someone with a basic understanding of electronic parts can help here. For example, if a capacitor is burst you can replace it; a diode - replace it, some types of transistors, etc. This way nobody needs to re code a module, have a special programmer, etc. Grasping at straws with ya.

Forget it, don't even try. That's the hard truth.

The PECU is the brain of the whole hybrid system. The car literally will not start without it functioning because it controls critical systems, including the high-voltage system handshake needed to power up. It's not just a battery issue; it's the car's nervous system.

Even if you could theoretically run it on gas only, the software is deeply integrated. No legitimate shop will "delete" it, as it would make the car illegal (emissions, safety) and likely immobile from endless error codes.

Your only realistic path is to seek a specialized independent European or hybrid shop (maybe in a major city like Houston or Dallas) for a used or repaired PECU. That quote is insane. A used part and a specialist might cut the cost by two-thirds. Start calling around; it's your only shot.

Hmmmm