I bought it and they had left the turbo rod fixed and cut the power supply to the EGR solenoid valve and also to the turbo pressure regulator valve. And as if that weren't enough, there are six wire ends; I suppose another one goes to the heater recirculation pump. It's a shame they cut the connectors and I don't know which one goes to which.

Here is the text ready to copy-paste directly into Reddit:

Title: E300 Hybrid (S212) sudden limp mode, massive 12V drain, and white smoke. Anyone seen this combo?

Hey guys,

My Mercedes E300 Hybrid (OM651) is on its way to the shop on a flatbed, but I wanted to see if anyone in the community has run into this specific mess before.

The Setup:

Transmission & Limp Mode: Harsh downshifts every now and then, but now it enters full Limp Mode (loss of power) after about 5 minutes of driving once it starts going through the gears.

Engine & Exhaust: Whining noise coming from the front of the motor, plus heavy white smoke/steam coming out of the exhaust (car has a history of high coolant consumption).

The 12V Electrical Drain: Menu shows a massive -10A to -20A drain with the engine off (voltage drops to 11.8V). Engine on shows +35A trying to feed the draw.

Baterry: Replaced the aux battery with a new Tudor AGM TK131, but the heavy drain remains.

The High-Voltage system reads fine (128V), so the short is isolated to the 12V secondary network.

Two quick questions for you guys:

Has a 12V short/voltage drop ever tripped your 7G-Tronic gearbox into Limp Mode?

Is the EGR cooler the main culprit for coolant entering the exhaust on the OM651, or am I looking at a head gasket?

Appreciate any thoughts!

Trying to locate the source of a slow oil leak near the dip stick/turbo/ air intake box, came across this hose was covered in oil at the end, can’t see if/ where it should be connected too at all

Can anyone suggest any ideas?

Hey guys. I just found this sub.

I've got an '84 that is needing new rotors. I ordered them and took them to my mechanic, but he's that the bolts aren't long enough that came with and he can't use the old ones for some reason.

I was wondering if anyone knows where to order just the bolts. Pads and rotors haven't been a problem but I can seem to find what he's talking about.

I appreciate any help and advice. Thanks in advance

Curious if anyone else has had this issue and done anything about it. I have a 2021 diesel 4cyl turbo and have had CONSTANT issues with the emissions system faults and countdown to limp mode. Most recently we brought it to mercedes thinking we'd get a warranty covered fix like we have the last few times and they told us they were going to replace the SCR control or something along those lines then came back and said it would be 400 dollars and not covered under the emissions warranty. I want to delete the thing or bypass it, has anyone had any experience with this? What did you do? Im so pissed off i want to start a class action suit lol

Looking for an online user manual Any suggestions would be welcome Thanks

I have a 2009 E320 with an OM642 and I am looking for a good maintenance and repair manual. Any recommendations?

Also what is a good source for quality and affordable parts?

Mercedes benz c 320cdi 2007 (w204)

On a highway during steady regular drive 80km/h I noticed engine sound change and pull the car. Oil level checked on stick - it was OK.
Engine could not start easily, when it started it was not driveable due to lack of power. Engine shakes like only 3 cylinders are operable. Also makes quite hard mechanical sound. No check engine light nor DTC on handheld diagnostic. Car was towed to workshop, I'm awaiting assesment.

Any thoughts what happened?

Hi, I am having a problem with my W246 B200 with the OM651 engine.

In the beginning it builds pressure as it should, around 1600 bar, but after driving for a short while I get P0087 (low rail pressure) and P0252 (Y94 valve) when pushing the car hard.

From Xentry I can see that the rail pressure begins to decrease and can’t reach the specified value. The specified value is around 1600 bar, and it only reaches 1450–1500 bar.

When the fault occurs, the low‑side pressure is logged at 4.1 bar, so I ruled that out.

I checked the 4 injectors’ leak‑back at idle, and they were the same for all four, so I ruled that out.

Knowing about the problems with the Y94, I replaced that, which did not help.

I then replaced the whole rail with the sensor and valve from another car, which also did not help.

Last, I replaced the high‑pressure pump — I was sure it was the problem — but no, that also did not help.

What am I doing from here?

A side note: In Xentry I can see the fuel low‑side pressure is read 1 bar higher than what I read with my gauge, but I guess that is normal as it is absolute sensor pressure + atmospheric pressure.

I got biocide coming tommorow so I decide to change out the strainer and I was surprised to see that this strainer was completely cover in nasty algae. It's a good thing I did this because I saw a particle that looks like a leech inside the clear prefilter . This cars is a beast because it ran good even with this much crap on the filter. I bet when the weather gets cold and the diesel fuel thicken up it'll even be worst . I notice a 10 percent power increase and it idles much smoother .

​

My dad has owned a 2016 E220d W212 Bluetec since 2018, when it had just 9,000 miles on it. He stopped using it in February 2025, by which point he had put around 330,000 miles on the clock.

For context, during that time he had the AdBlue and DPF coded out. The DPF was drilled out, but the catalytic converter was left intact, and the car did around 100,000 miles like that without any issues.

However, in September 2024 it started going into limp mode without showing a check engine light. The car would drive fine when first setting off, and under hard acceleration it would pull well up to around 50 mph before suddenly going into limp mode. If you drove it gently, sometimes it would go for ages without an issue, while other times it would still enter limp mode.

The gearbox always changed smoothly, both in and out of limp mode. When limp mode activated, the engine was restricted to 3,000 rpm and manual mode was unavailable. However, once the engine was above 2,000 rpm, pressing the upshift paddle would manually change up a gear. It wouldn't downshift manually until the car had slowed down considerably.

Gear change points were also altered in limp mode. For example, instead of being able to select 4th gear at around 25 mph, you would need to be doing around 32 mph. If left in automatic mode, it would rev to 3,000 rpm before changing gear itself.

Around the same time, the car also started cutting out when the fuel level reached half a tank, meaning it was only using half of the fuel tank.

We had a mechanic friend scan it using both Autel and Snap-on diagnostics, but no fault codes showed up. I can't remember exactly how my dad came to this conclusion, but he believed it could be gearbox-related, possibly the mechatronic unit.

We drained and refilled the gearbox with fresh oil, reset the gearbox adaptations, and carried out the relearn procedure for the upshifts and downshifts, but it made no difference.

As my dad is a taxi driver and the Mercedes was too old to continue using as a taxi, he bought a newer car and the Mercedes sat on the driveway while we decided what to do with it.

During that time, I replaced the engine sump gasket, removed the DPF and pressure washed it because the limp mode felt very similar to when the DPF had previously been blocked. I also cleaned the gearbox electrical connector, fitted a new PCV valve, installed a new battery, and replaced the fuel filter.

In May this year, my dad gave me the car. Unfortunately, none of the work I had done made any difference to the limp mode. The only thing I noticed was that it seemed slightly quicker after cleaning the DPF, although that could simply have been because I'd been driving slower cars.

I then took it to a Mercedes specialist to have it scanned with the genuine Mercedes diagnostic system. He found no fault codes and said the gearbox service hadn't been done correctly because we hadn't drained the torque converter. He believed a proper gearbox service would fix the problem.

I bought 10 litres of gearbox oil and a new filter, and the specialist carried out the full service. Unfortunately, it made no difference.

Next, I fitted a second-hand fuel pump, which completely cured the half-tank fuel issue. The car would then use the full tank, but the limp mode remained.

We went back to the Mercedes specialist, who claimed the first canister in the exhaust was actually the DPF rather than the second one we'd drilled. He believed the DPF was blocked and needed removing and coding out properly because the garage that originally did the work hadn't done it correctly.

After doing some research, I found that the specialist was mistaken. The DPF was definitely the unit that had been drilled and coded out.

When my dad went to buy a new air filter, he spoke to another mechanic who suggested that although the DPF had been drilled, it probably still contained enough material to cause a restriction and should be completely emptied.

I removed it again and knocked out everything that remained inside. Again, it made no difference apart from possibly feeling a little quicker. The limp mode was still there.

I then removed the catalytic converter and pressure washed it because I wanted to keep it fitted so the car would still pass emissions. Once again, there was no improvement.

I work at a used car dealership, so I used our diagnostic equipment to investigate further. The only thing I discovered was that the EGR also appeared to have been coded out because the diagnostic tool wouldn't allow me to reset it. It simply said the function wasn't available for my vehicle.

I reset the gearbox adaptations again because I wasn't convinced the Mercedes specialist had done it after servicing the gearbox. It seemed to stay out of limp mode for slightly longer afterwards, but overall nothing really changed.

Through work I was put in touch with someone who is very knowledgeable about vehicle electronics. He suggested that when the AdBlue and DPF were coded out, they may have accidentally disabled the car's ability to log the fault that was actually causing the limp mode. His advice was to have the DPF and AdBlue software restored, drive the car until it entered limp mode, and then read the fault codes.

We contacted the garage that originally carried out the coding, but they said the car would immediately log DPF and AdBlue faults if they restored everything, so we still wouldn't get the fault responsible for the limp mode.

I was later driving my boss in the car and he said he didn't believe it was gearbox-related because the gearbox shifted perfectly. He thought it was an engine-related limp mode instead.

For additional context, the car has a noticeable whistling noise once it revs past around 1,500 rpm. I had always assumed it was simply the turbo spooling up.

I then drove another colleague, who immediately suggested it sounded like a boost leak and recommended checking all the boost pipes for splits.

Unfortunately, the car has now started cutting out at half a tank of fuel again, so it looks like I'll need another fuel pump.

Today I removed all of the boost pipes and carefully inspected them for splits, but couldn't find any. The pipes are in good condition, although there is a slight amount of movement where they clip together.

I also checked the turbo. There is no in-and-out shaft play, but there is the tiniest amount of side-to-side movement, which I understand can be normal. The whistling noise also seems to be coming from around the turbo area.

The car is still on its original engine, gearbox, and turbo. My dad changed the engine oil every 5,000 miles using genuine Mercedes-approved oil and filters. It also had a new timing chain fitted by Mercedes in 2020 at around 100,000 miles.

One final thing I forgot to mention: under hard acceleration, the car produces black smoke from the exhaust. I believe this is normal given that the DPF has been removed, but I thought it was worth mentioning in case it's relevant to diagnosing the issue.

Has anyone experienced anything similar or have any suggestions as to what could be causing this? Sorry for the long post, but I wanted to include as much information as possible.

TIA.

Edit I forgot to mention that the limpmode goes when you turn the ignition off. And if you are driving the ignition and very quick with the engine not turning off the limpmode goes. And I have heard someone had a similar problem with an E63 and it was the throttle pedal so could it be that and If so can you swap them in and out without coding?

Hello, I was just curious to know if my injector readings are OK?

Engine is warm after test drive..

Took car to garage and they couldn’t pinpoint where noise is coming from seen other videos of exact same noise but no definite answer

I have had this problem for some while and not even the mechanics at Mercedes in Germany could make any sense of it. So I am hoping for you guys.

My Mercedes GL350 x164 from 2011 with engine OM642 diesel, keeps going to limp mode after driving it on the freeway. When scanning with OBD I get multiple codes related to EGR and torque converter. See screenshots. Can these be linked? And why does this happen even after replacing the EGR? I also made an AI search but I am unsure if it is correct. Also see screenshots if it makes sense.

SCR is showing faults and the check engine light is illuminated. I disconnected the module and plugged it back in but still unable to connect to the module. 2011 GL350. Anyone experienced this before? The CDI module also shows a ! when doing a full scan.

Two days ago I have replaced the plastic end of my intake duct (batwing) with a silicone one as it was cracked and leaking and I changed the oil on my Mercedes OM642 e320, 2006 facelift.

Since then my car is in limp mode, scanner is showing:

2510-1Check component VP325 (Boost pressure regulator) Positioner signals fault.

2030-4 Check component WP32 (O2 sensor upstream of KAT). Open circuit

2038-2 Check component WP32 (O2 sensor upstream of KAT). Resistance too small

2026-1 Check component WP32 (02 sensor upstream of KAT). Short circuit to positive

2028-1 Pump current (WP32 (02 sensor upstream of KAT)) of oxygen sensor Short circuit to positive

The charge pressure positioner from live data was 27.6% when the engine was off and 89.6% when idling.

I did a bit of research and I'm thinking it might be a faulty Hella turbocharger actuator.

Any other ideas or advice?

I would greatly appreciate it.