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Need some help. Bought this GL back in April and had a lot of coolant issues. Smell and leaking so I replaced Water pump, thermostat, Expansion tank and cap, Belt, Hoses, and the Aux water pump. Coolant smell and leak went away, but now whenever the the key are in the ON position, the Aux pump will stay on pulling all the coolant out the expansion tank tripping the CHECK COOLANT LEVEL. Ran the iCarsoft code reader and got these two codes. Anyone have any insight on why the pump stays on and what these two codes mean or how I can fix it? Any help would be greatly appreciated. Dealership said they couldn't find anything but I did.
0155
State: Historic
Component Y110(three-disk thermostat valve) has an open circuit in the wiring. (P0597)
0695
State: Historic
M4/7(Engine and AC electric suction fan with integrated control): Output stage
That haven't been enabled since the summer months or hot days when the A/C was being used. even then the pump stayed on once the keys were in the on position or car started. Stupid things keeps running and it sucks all the coolant out the expansion tank and upper hose gets hard like rock.
Those are historic codes. I think that means they're not current, right? That's probably why the dealer said there wasn't any codes. To start with, try resetting/clearing and see if anything comes back.
And by aux pump you mean the function that is enabled by pressing the A/C REST button on the HVAC panel?
A/C rest runs the pump and fan for 30 mins after engine shutoff to maintain cabin temp.
try unselecting it if it’s selected.
Wow. 130k miles and I had no idea of this functionality. What the heck is this pump? The AC compressor is run by a belt. So is the water pump. There is some sort of pump on the line to the expansion tank?
Originally Posted by DennisG01
Those are historic codes. I think that means they're not current, right? That's probably why the dealer said there wasn't any codes. To start with, try resetting/clearing and see if anything comes back.
Ditto. Make a habit of clearing historical diagnostic codes.
Wow. 130k miles and I had no idea of this functionality. What the heck is this pump? The AC compressor is run by a belt. So is the water pump. There is some sort of pump on the line to the expansion tank?
The function works great. There's a small, electric pump that continues to circulate coolant until it cools down to a certain temp (and can no longer supply warm air) and then it will turn off. I have the same function on my '97 BMW as well - it's a nice feature.
Last edited by DennisG01; Jan 12, 2021 at 05:47 PM.
Contrary to popular belief, the aux pump is not only uses to pump water to the cabin heater whilst in REST mode, but it works constantly to circulate water to the cabin heater matrix although it may be at variable speed. If you're having heating issues, then this may be the culprit.
Is the aux pump the little device plumbed into one of the lines going to the reservoir? I wondered what the purpose of it was.
Yep, that's the aux pump which works in addition to the main water pump of the engine block. The aux pump job is to supply the hot coolant to the cabin heater matrix. It looks like this below.
Bosch auxiliary PAD pump bosch 0 392 023 004 bosch 0 392 023 004 on W212 E200 NGT
The circulation pump, referred to by some as the aux pump, is a band aid and a cheap commodity band aid. The pump is widely used across MB models and is known to fail.
It is a band aid because the main water system and pump is insufficient for engine cooling and cabin heating needs under all vehicle operating conditions. So a circulation pump is needed.
And it powers the uncommon REST function, if present on the vehicle.
The circulation pump, referred to by some as the aux pump, is a band aid and a cheap commodity band aid. The pump is widely used across MB models and is known to fail.
It is a band aid because the main water system and pump is insufficient for engine cooling and cabin heating needs under all vehicle operating conditions. So a circulation pump is needed.
And it powers the uncommon REST function, if present on the vehicle.
Funny you should mention, since when I went for a drive at about 15F, I noticed the cabin heater was insufficient. Maybe my aux circulation pump no longer functions. I should check to see if the REST function works.
I always wondered why the bizarre name REST. The AC needs to take a break?!?
REST is German for remainder or residual - Restwert.
Holy crap guise, he's right. And for some strange reason I assumed it was a verb.
Fun fact: German is an often-times hilarious language, as speakers do not make new words but simply string smaller words together. The longest German words easily trump our own supercalifragilisticexpialidocious or antidisestablishmentarianism: Rindfleischetikettierungsüberwachungsaufgabenübert ragungsgesetz
(das, 63 letters)
This hyper word references a "beef labeling regulation and delegation of supervision law." This was a 1999 German Word of the Year, and it also won a special award as the longest German word for that year. It refers to a "law for regulating the labeling of beef"—all in one word, which is why it is so long. German also likes abbreviations, and this word has one: ReÜAÜG.
Hence we are drivers of Gelandewagen Luxus - the first being something like on-land vehicle. Restwert actually means residual value or residual amount. The German word "rest" translates directly to one meaning of the English "rest".
English is a bear to learn because of multiple meanings, but it does make the language more compact and makes for terrific puns and riddles.
This is a sign of failed aux circulation pump . Not enough cooland flow with out the aux pump running .
You mean flow >through the heater core<, right?
I wonder if the aux pump switches on and off based on the cabin thermostat inputs. Something else would have to split the heat flow, I guess. Or does the system just route air flow?
The circulation pump, referred to by some as the aux pump, is a band aid and a cheap commodity band aid. The pump is widely used across MB models and is known to fail.
It is a band aid because the main water system and pump is insufficient for engine cooling and cabin heating needs under all vehicle operating conditions. So a circulation pump is needed.
And it powers the uncommon REST function, if present on the vehicle.
I’d speculate that having a “helper” pump is a fuel economy measure, as clearly this pump isn’t needed when in air conditioning mode ... and that this is a strength rather than a weakness, representing great, creative engineering. And, yes it’s a neat solution as dual purposed to provide REST function ... which obviously the engine water pump couldn’t.
So. Here what's been going on in the last week. Had it at the "EURO" vehicle show and I was told that my thermostat was not Mercedes and that could be the culprit. So I went back to the dealership and ordered a new thermostat, expansion tank, cap, Aux cir water pump, Heater control valve that in the back of the engine, coolant temp sensor, coolant and new fuses. Had everything changed, took the truck for a spin and what do you know 3 miles on the highway and the check coolant level came on. All the coolant from the expansion tank was gone. I opened the cap slowly and it came right back. I have no clue WTH is going on because the dealership couldn't figure out what's going on. I had to drive about 100 miles today and I made a few stop since the check coolant level kept coming on, so I had the cap loose and I made it all the way home. it only went down a little bit. as soon as I stopped the pressure built back up and started spilling coolant from the expansion tank. if anyone has any ideal what's going on here please jump in. I feel like something is not breathing. when the cap is on tight, the coolant disappears. when its lose it stays in the tank. ooh and I noticed the main fan was running loud today. thing was spinning out of control until I started driving but the temperature was at 90 the entire time.
For what it's worth, parts darts gets expensive fast. Really sucks to hear it didn't fix the problem. I changed my coolant - drain and refill - and had zero issues.
When the cap is on tight, the pressure in the system raises the boiling point of the coolant. However, unless the motor is overheating, the temperature throughout the system should not be in excess of the boiling point even without pressure. 90C is below the boiling point of water, let alone the coolant mix. And the temperature should not be much different throughout the system; motors like to at a fairly uniform temperature.
Possibility: Some part of the cooling system is barely getting circulation, and when the water pump stops, the coolant boils in that spot. This would fit with the fan running at maximum speed, but not with your gauge reading 90C. Is there any chance there is some crud blocking a coolant passage somewhere?
Did you run the cabin heater as normal - that is, to ensure coolant flowed through the heater core? If you still had trapped air, it would shrink upon pressurization and then expand when the pressure is released, pushing coolant back into the tank. Usually it's not this hard to burp the system, though.
If you can probe the cooling system with an Autel or Icarsoft or DAS, you can find out what the temperatures are, assuming there is more than one temperature probe.
I think there has to be a Block somewhere. no clue though because when I drained It myself, I filled it with water, I removed the hose that connects to the heater valve control in the back of the engine and put compressed air and it forced all the water out the back. I then hooked up the garden hose to the heater core hose inlet and watched clear water come out the outlet. so im honestly lost man. And when Mercedes drained and pressure filled it, it worked fine for 2 days then started doing the same thing again.
Assuming there is blockage, it would not matter if it were in the heater core. It would be somewhere in the block or head.
Try back-flushing the block and head. Disconnect the bottom radiator hose, remove the thermostat, and push water in the top and see what comes out the bottom. Use a big hose without restrictions on a hose bibb; you want to make sure you get a lot of water flow.
Catch whatever comes out for inspection. Put a big sieve in a bucket. If it's in chunks, try to reassemble it. There might be pieces stuck in the radiator, too, and you might need to back flush that, and the heater core, as well.
Before you do that, make damn sure the heater core isn't full of air. Let the thing run with the heat on. It being winter, you've probably already done this, but I just wanted to verify.
Something is pressurizing the overflow tank causing the volume of coolant in there to temporarily disappear, then reappear when the tank is depressurized.
that sounds like a uncommon mode of a failing headgasket.
have you done a chemical test on your coolant for exhaust gases?
Might want to rule out headgasket. It’s plausible that temps will stay normal and that you have no oil/coolant mixing going on until it fails completely.
Last edited by Max Blast; Jan 21, 2021 at 03:49 PM.
An opening between the exhaust and the coolant would result in coolant going into the exhaust when the engine is warm and there is low exhaust back pressure. Seems like that would be pretty hard to miss.
What about the “desiccant bag failure” seen in sedans? Does the GL have a desiccant bag in the HVAC system?
on the other hand, diagnosing a head gasket failure can be done by these tests:
chocolate colored sludge on radiator cap or oil filler cap
cooling system pressure check
cylinder compression and/or leakdown
Coolant smell (sweet) from tailpipe
steam from tailpipe
loss of coolant over time
”washed” clean tops of pistons
“washed” clean spark plugs
external oil leak
coolant in oil drain container
oil in coolant drain container
misfire
rough idle
I did a pressure test so did the dealership twice and it didn't fail. No smudges in any oil or in oil filler cap. the Euro shop thought the head gasket was failing because there was oil in the back but realized it was the oil cooler. the gasket was gone and they had that replaced too.
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