I have a Mercedes-Benz W221 equipped with the M273 engine, which has a heater shutoff valve located at the rear left side of the engine (near the camshaft area).

What surprises me is that the heater shutoff valve remains in the open position even when the HVAC temperature setting is turned to low or switched off. When I change the HVAC temperature setting from low to high, I can see that the heater request value changes from 0% to 100%. This indicates that the HVAC control module is sending the correct request signal to the ECU. However, the ECU continues to keep the heater control valve in the open state unless I manually actuate the valve to close it.

I have already replaced the ECU, but the issue still persists.

Are there any sensors on the M272/M273 engine that directly influence the open/close operation of the heater shutoff valve?

 

can you write that in a way I can understand...

heater shut off value = heater valve with three pipes and they go wrong ?
there is cleary something going on as the heater gets worse with age and a new engine stat makes zero difference - and on mine a new heater valve did nothing either
the OEM software didn't and there are 4 iterations trying to fix it after they realised they'd made 37,000 and the REST button never worked on any of them - then they gave up and made a new model and just moved on

 

some claim the electric pump wears out (Part 10) but its a pain to fit
Part 170 is the heater valve, rear left of the engine bay (looking from the front) on the firewall

 

I mean the below heater valve, this heater valve is mount on left side of engine and my car is not equipped wiyh 3 pipes heater valve located behine firewall, however I think both of them perform the same function: 12V supply from ECU then valve close, without power valve stay at open state and let a hot water go to heater core.

Issue of my car is related to control signal from ECU (12v) to this valve, valve only close when I using scan tool to close the valve otherwise valve stay open state even the temperature dial already set to low and heater request is 0%.

is there any other factors to keep this valve open?

 

Does your car have rear Aircon?

 

I don’t recognise the valve shown in post #4

cars with rear AC have a very similar layout to normal cars - with the electric pump and heater valve as per post 3 - but down inside rear of the front wing (on my car right hand side), is another silly valve and three pipes - as used on the w220 that controls individual rear seat heater flow - they go wrong leaving the trim to melt as it get stupidly hot when the pintle valves leak by - I think that electric pump is the rear seat REST setup

aka this




for $15 you can fix the issue

 

is this the other magic heater valve that clb110099 eventually found on his problematic set up - if so I wonder if this is in conjunction with the madness that is the three way engine cooling stat

see schematic beneath this




Part 150 SHUT-OFF VALVE CYLINDER HEAD, LEFT REAR 001 A 27 220 000 31 - $63.91
Part 153 looks like a similar idea - but they don't call it that 153 CONNECTION PIPE SOCKET CYLINDER HEAD, LEFT REAR 001 A 27 220 000 54 - $15.35 ???

 

That looks like an engine warm up valve for emissions BS rather than part of the heating system.

Especially as it's listed with the water pump rather than the HVAC....

To answer your question, the only reason it would remain closed would be in extremely cold temperatures to enable the engine to maintain an optimum temperature.

Assuming you're in Vietnam I suspect that it's only actually closed for a couple of minutes following a cold start.

Not currently at home, but the wiring and function block diagrams on WIS may well show that it's triggered by the thermostat temperature and controlled by the ECU interpretation of that thermostat signal.

 

My car is a Mercedes-Benz S500 equipped with rear air conditioning. The rear duo valve mentioned by Botus in post #6 is working properly, and the retrofit kit for the rear duo valve has already been installed.

The heater shutoff valve I mentioned in post #4 is definitely for heating purposes. It is widely used on vehicles equipped with the Mercedes-Benz M272 and Mercedes-Benz M273 engines in this market.

However, I believe the heating system configuration on the Mercedes-Benz S-Class differs depending on the market. From what I understand, for the US/UK market, the component I referred to in post #4 is simply a similar coolant pipe without an electric solenoid. In those versions, the main heater control valve is a 3-port valve (motor-controlled) located behind the firewall.

I am confident that shutoff valve #150, located at the rear left cylinder head, is controlled by the engine ECU on my vehicle. In contrast, on US or UK spec W221 models equipped with item#153 and the 3-port heater valve behind the firewall. The 3 ports heater valve may not be controlled directly by the engine ECU, but possibly by the Upper Control Panel (UCP).

Therefore, I suspect that if my car has been fitted with a US-market component, the heater shutoff valve at the rear left of the engine may remain permanently open, since heater control would then be managed by a different control unit. As my car is a European-spec S500, I suspect that a previous owner may have replaced a component (possibly with a US-spec part), which could be the root cause of the issue. I will check the coding of the UCP and other related control units and will update once I find more information.

 

main dealer will be able to tell you if you need Part 150 or 153

I doubt UK is any different vs European spec
USA is different to Europe with a more powerful AC and the silly Max position on heater knobs
I can imagine 150 vs 153 could be different if you have Rear AC or Not

file has two sheets one the engine parameters and the other the HVAC module beside the blower motor

 

I will have a look at mine and see what it has fitted... UK S500 without rear AC.

Yes it's part of the heating system but only indirectly because it connects to the HVAC plumbing, but the fact that it is physically attached to the block and is controlled by the engine ECU tells you it is more specifically part of the engine cooling system.

It would never be expected to operate in response to HVAC settings.

 

Ok, have done some digging... My late 2006 SWB UK S500 without rear A/C has it fitted. Otherwise, there's absolutely bugger all information about it on WIS. It's only upto a certain build date/engine number.

P/N A272 200 00 31

It is the control valve for the low temperature coolant circuit. Basically it is closed during a cold start in order to short circuit the coolant flow to keep it in the block until the engine warms up. Then it remains open.

The low temperature coolant circuit is an integral part of the overall system.

Unless it's leaking, there's zero reason to worry about it or change it. If you suddenly suffer from rapid engine temp spikes that might suggest failure of it, then at that point you might want to replace it. Otherwise find something else to worry about.😉

FOR MODELS UPTO: 22/10/2007 Engine Number 30196899

Valve, cylinder head, left A272 200 00 31.

FOR MODELS FROM: 22/10/2007 Engine Number 30196900

Connection fitting, cylinder head, left A272 200 00 54.

Absolutely nothing to do with the HVAC, specification/options fitted or market.

Zero ambiguity.😉

 

I have worked on many Mercedes-Benz S-Class and Mercedes-Benz E-Class models equipped with the Mercedes-Benz M272 or Mercedes-Benz M273 engine, most off them are using the cylinder head heater shutoff valve A272 200 00 31 and I am 100% certain that this valve is powered and controlled by the engine ECU for cabinet heating purpose. When there is no heating request from the driver, the ECU supplies 12V and the valve closes. If you slowly adjust the temperature dial from cold to hot, you can clearly observe the valve changing state from closed to open in response to the heating request.

 

Thank @BOTUS shared the file related to coding of the ECU and HVAC, from the coding file I realized there is a coding on ECU related shutoff valve heating and it wrong coded on my car leading shutoff valve open or close is not control by ECU, I changed coding ECU of the shutoff valve to "fitted" then I got what I want: heating shutoff valve only open when heating request by driver, otherwise it remain closed and hot colant not enter heater core.

 

What is the build date of your car? Whether it should be fitted or not is dependant on this.

After 22/10/2007 and that valve is not a even a valve at all but simply a connection piece.

 

35th line of coding in my file - Row 45 in Microsoft world

I need to check if I have that valve - mine with rear AC is set off too

what was the issue you were chasing ?
my heating went to **** about 4 winters back - mate with a CL500 had the exact issue at the same time - every winter you have to add 1C to the numbers to get the heat you had the year before - although after a cooling stat change in the summer it seems even worse this year
at the time both cars were 100% std on engine stuff

 

Whether your car has it, or not is clarified by EPC...

FOR MODELS UPTO: 22/10/2007 Engine Number 30196899 Valve, cylinder head, left A272 200 00 31. FOR MODELS FROM: 22/10/2007 Engine Number 30196900 Connection fitting, cylinder head, left A272 200 00 54.

Specification is irrelevant, it's based on build date.

I didn't trawl through the wiring diagrams to investigate it any further. WIS offers no information on the installation or purpose of either part in the W221 in either Engine Cooling or HVAC against my VIN.

Incidentally, I can't open the file.

 

My car is a 2005 model. However, I have encountered many Mercedes-Benz S-Class S350 (WDD221156xxxxxx) units manufactured in 2008, including facelift versions from 2009 and 2010, both with and without rear air conditioning, that are equipped with a heater shutoff valve located at the rear left side of the engine.

Based on my understanding, the heater shutoff valve (or a simple connection pipe in some versions) is independent of the rear air-conditioning option.

• If the vehicle is equipped with a heater shutoff valve at the rear left of the engine, it will not have the 3-port heater control valve behind the firewall.
  
• If there is only a simple connection pipe at the rear left of the engine, then the vehicle will be equipped with the 3-port heater control valve behind the firewall.
  

The advantage of the 3-port valve is that it is motor-controlled and can regulate coolant flow proportionally, rather than operating in a simple open/close mode like the heater shutoff valve.

 

interesting about vehicle age -

do you have Microsoft excel installed ? it won't open with out it

here CSV (text file) but now we need to add two files as CSV can't do mulipage documents

 

Sorted, I have Office 365, but phone was trying to open it with a totally unrelated and unsuitable app🤦

I checked EPC both with my full VIN so it only shows parts as it left the factory, and also WDD221071 which then shows everything available regardless of production date or specification. Obviously both list the option details and production break points as well as superceded parts. The latter VIN search is handy for reverse identification... The early-ish cars have all sorts of nuances that the later cars don't. Same was true of every previous S Class except perhaps the W116.

That valve/connection has no option code attached to it, usually the option code in blue, just upto/from and the engine numbers and dates.

I am about to spend a couple of days rebuilding the front brakes and lower arms, so whilst I am under it, I will explore the plumbing and report back. I suspect that it's not the only supply to the HVAC circuits.

 

How does it behave from a cold start?

It's not permanently closed regardless of valve position. There is a bypass in it which feeds from the HVAC plumbing.

The supply from the water pump to the heater runs through the right hand wheel well and up across the front of the brake servo to the HVAC valve.

I think you have the coolant flow at the back of the engine backwards. It flows out from the water pump and back through the valve you're puzzled by.

 

my car states in EPC it has the solenoid version of the valve as per pic 4, and the heater valve, and the duo valve for rear AC

 

The valve opens only when there is a heating request (i.e., when the interior temperature setting is higher than the ambient temperature).

Therefore, during a cold start:

• If no heating is requested, the valve remains closed.
• If heating is requested, the valve will open.

 

Ok