I need some help from the guru's. I'm a GM master tech myself, but these benz are a little different from even our cadillac's.. and I don't have xentry yet. Plan to get that all setup on a dedicated pc soon. I heard @MBENZTECH is the go to for that, but mbworld wont let me message.

So the issue I'm having is a yellow coolant light popping up and it sets P0C7300, circulation pump 1 for the low temperature circuit has a malfunction. P0A0500 the actuation of the circulation pump for low temperature circuit has an open circuit. P00B700, coolant flow low.
I pulled schematics and voltage drop load tested the circuits for both low temp pumps and they're good. Actuation tested all 3 coolant pumps, 43/4 under the intake would only run for a second and stop, didn't sound good. Replaced it with a genuine pump from the nearest dealer. Bled it really good by running the pumps on and off etc. The pump now runs continuously when commanded. Light stayed off a few days of in town driving. Hit the highway for a 600 mile trip, halfway the light is back. Had no choice but to keep on as it was late and no signs of overheating. I mean that pump only goes to the trans cooler. So yea subsequently it had also set a code for trans overtemp @ 240 once it got to the dealer. They said ahh it's air, so they bled it. I get it back and 5min down the road the light is back. I take it back, they bled it 3 more times. So I leave to head back home. Two hours down the highway the light is back. It's not setting the coolant flow code anymore, and I have also noticed when it starts after a hot soak, it runs rough for a few seconds. I can hear air in the heater core when the main circuit pump first starts. I'm like where is this thing getting the air? Compression leak maybe? That's my initial thought based on my 10 years exp with GM, but it's not overheating even on hard steep hill pulls on the highway.

@Mecopel We have replaced several of those pumps but we use a vacuum filling system after repairs and we have not had any issues. For that vehicle, the Tactrix Openport j2534 device (original) and Xentry passthru is more than enough.

Yes I did use a vacuum filler. And also ran the pumps vigorously to get the air out. The dealers have tried to bleed as well. Light still popping up.. I have a j2534 GM MDI 2 that I assume would work with xentry passthru. Just need to find someone to get the xentry software from.

You can try from here,

https://www.mbenzsoft.com/

A member posted on a thread related with Carplay activation about this site, I am sure that they are the same like any around here

@Mecopel The GM MDI2 actually works great with Xentry passthru. I used for several years and I still have it but no longer use it with Xentry because we now have the actual genuine Xentry kit 4's.

@MBENZTECH Yes I was able to get it all setup and working with the GM MDI 2. If only Xentry could wave a magic wand to tell me how the air keeps getting in the low temp circuit haha. Can you code and whatnot with mdi 2? What are the limitations do you know?

Maybe the air came in from where the coolant goes out...
With Xentry you can make diag, tests and repairs based on procedures, pictures, schematics.

For coding you will need DTS Monaco or Vediamo

Failed cylinder head? Standard feature on MB four bangers.

I have seen the bulletin for cylinder head yeah, but the failure is for worn valve guides.. I would think if the head or gasket was leaking compression into the coolant, it would overheat on the highway. It doesn't overheat no matter how hard I push it..

@Mecopel With Xentry/DAS offline you can diag, read codes, clear codes, actual values and activations. Online programming with Mercedes servers is not possible. I use the full Xentry kit 4 kit and also the Xentry passthru in the shop. But those are legitimate licensed through Mercedes. If you want to do any coding or flashing for your car, you can use DTS Monaco.

And most of all, Xentry (legit or not) offers the most advanced conducted test for troubleshooting in the automotive industry

I've noticed that Xentry is a bit more complex than GM's GDS that I've been working with for years. But GDS is evolving quite a bit as of late also with the new wave of EV's.

Hey @Mecopel , did you ever resolve this issue? I am running into the exact problem you're having. It started with a leaking coolant pipe, replaced that pipe and then this light popped up. Proceeded to change every single water pump and thermostat and after driving a week, it comes back again. Did you ever figure out why it was doing this?

Yes I did. Bad news for you though... it ended up being leaking head gasket, started misfiring in the morning only after about 1000 miles after the coolant light started popping up. Low compression cylinders 3 and 4. Leak down test revealed exhaust valves on cylinders were leaking 40% and 60% respectively. The head gasket leaking stained the cylinder wall coating of #4. I replaced the entire cylinder head many thousand dollars. Now only 2k miles later, engine knocking. It's parked because I'm almost fed up with the car lol. 12k for an engine is nuts. I may rebuild it idk yet I will have to see if cylinder 4 coating stains affect the compression before I decide. 71k miles on it now

Appreciate the response man. What a horrible engine. Mercedes really did us dirty with this one. This is actually the worst case scenario for me, I don’t even know what to do at this point, already spent so much replacing all the water pumps, thermostat, the whole crankcase. This just sucks. So an engine rebuild is probably the only correct path to resolve this?

Just because mine is knocking doesnt mean for certain yours will. You may get lucky with just the head gasket, if your head is still good. But yeah for me I'm very disappointed in this engine it has been the worst experience I've ever had. And from a newer car... I figured a 2019 wouldn't have issues like this.

Yeah, I suspect this problem will become more and more common as other cars get up to the mileage that we're at. I also have a 2019 with 82K (my wife drives it). The more research I do, the more I see this head gasket issue being a common problem. Do you think the auto engine cutoff has something to do with it? There's no way turning the engine on and off can be good for these cars.

The nearest dealer told me the cylinder head failure is so common, they stock 5 heads. No i don't suspect the auto stop would cause it, I'm a GM master tech myself and our 4 cylinder GM cars do auto stop too, caddilac included.. but they rarely have issues like cylinder head or gasket failure. I'm really regretting betraying my own Cadillac brand, with a far superior 6 yr/70k powertrain warranty 😂

Yeah, I love the way these cars look, but that engine design is absolutely terrible. I am so disappointed at Mercedes for selling a car that starts having problems at 70K miles, horrible engineering. I don't think I will ever buy another Mercedes again to be honest.