08 CLK350 M272 P2004/0521

[kevm14]

Still learning how to use DAS (currently in simulation mode because the car is elsewhere).

Here is the code setting criteria, FINALLY.

I didn't realize you could just click on see more info and then F2. It opens an HTM file in the browser. Then just print as PDF. I found it by searching the path before I realized you can get to it directly from DAS (duh).

20260316_075839.jpg

Interestingly it states the MIL is not illuminated. So that part tracks. Here is the exact 0521 code setting logic:

- Fault if the signals from both position sensor do not change from about 5V to about 0 V. The fault must occur many times. Possible causes: tumble flaps are not actuated for an actuation, vacuum supply or aneroid capsule defective, tumble flaps are swung back into the test position after the last actuation, short circuit to ground on both position sensors for the tumble flap, linkage.

The checking duration is "less than 5 seconds." It would make more sense if the error state needed to exist for 5 seconds but I don't know what less than 5 seconds means.

Or I'm being dense and it just means "if the voltage state of the hall effect sensors don't change from 5V to 0V in less than 5 seconds, that is an error condition and it needs to happen 'many' times before setting the code.". German translations can be an impediment.

Prereqs:

- Battery voltage 11 to 16 volts
- Blocking time after starting, approx. 26 sec. expired
- No electrical fault on intake manifold tumble flap switchover valve
- Engine load less than approx. 30%
- Coolant temperature greater than 60°C

And an interesting known bug:

On an extremely hot engine compartment it is possible that a fault is entered. Delete fault if the Tumble flap switchover is OK (linkage, vacuum supply, aneroid capsule and tumble flap do not jam).
Exactly observe installation of a tumble flap position sensor at the prescribed torque of 6 Nm!

The tumble flaps are moved via an aneroid capsule and a rod to the flap shafts.

The intake manifold tumble flap switchover valve is integrated in the vacuum line to the aneroid capsule. If it is deenergized, the aneroid capsule is ventilated and the tumble flaps are lowered in the intake manifold (closed position).

If the intake manifold tumble flap switchover valve is actuated by a ground signal from the ME control unit, vacuum passes from the intake manifold into the aneroid capsule. The tumble flaps are actuated and turn in the intake manifold. This closes the intake manifold by around 50 %.

To diagnose the tumble flap switchover, the position sensors detect the mechanical limit positions of the shafts. The swivel range of the tumble flaps between completely swiveled in or out is approx. 56°.

There are two cylinder magnets with different polarities attached on every tumble flap shaft. Once the tumble flaps have swiveled out a cylinder
magnet as on the Hall sensor and the position sensor transmits. The signal at the ME control unit is about 0 V (tumble flaps actuated).
Swivel the tumble flaps back again and the other poled cylinder magnet on the Hall sensor is in the rest position. The position sensor opens and interrupts the connection to the ground. The signal at the ME control unit is now about 5 V (tumble flaps not actuated).
The position sensors must switch no later than approx. 5° before the respective limit position. For reasons of tolerance, they may also switch up to approx. 16° before the limit position.

[kevm14]

There was a late production high output M272 with option code M014 but in the US this seems to have only been used on the facelift R171 SLK, 09-11. However, it looks like ALL of them received it. That's what it looks like in EPC (engine code 272.969 is associated with all R171.458s) and the very first random 09 SLK350 VIN I ran showed code M014 in the data card.

Output went from 268 hp to 300/302/312 hp depending on where you look. Notable changes to boost output included:
- New composite intake manifold and I think they deleted all variable things from this. The emphasis became top end power and probably lost some low and mid-range torque
- M273 throttle body (fun fact: the original M272 used the M113 throttle body. This is very GM and I approve)
- Cams
- Pistons
- Valves, rockers and springs
- The cylinder heads have a different P/N but there is no way to know if that is only because of the valvetrain differences or if they changed the casting. If I had to bet I would say they did NOT change the casting. FWIW they did not change the exhaust manifolds when they added the M014 engine to the facelift SLK350.
- Increased redline to 7,200 rpm

While this is interesting because it seemingly improves a reliability sore spot while increasing power, you lose low and mid-range torque, and without the other mods, probably don't gain the whole difference AND this manifold is unobtanium (maybe the most important part).

This was evidently popular enough at one time because FCP Euro offered a kit:
https://www.fcpeuro.com/products/merced ... 2721403001

Price was reasonable, too.

That said, an 09-11 SLK350 with 6 speed manual is probably pretty cool considering they made M276 power before that engine even came out.

[kevm14]

Based on reading the comments from the Uro linkage repair kit video, they only recently released their replacement manifold to the market. As I indicated in a prior post, this is the cheapest new manifold option that you can get on Rockauto.

I also have been watching videos and this issue has been around for 11 years or more. I think there are multiple failure modes. I have no hands on data other than some personal (and Adam) anecdotes plus all the online "data" but here are some possibilities:

1) The main pivot seems to go nearly over center and puts a lot of strain on the ball/section of the pivot. Someone mentioned something about a return spring failure, but I don't fully understand the causal chain there. It does seem like snapped dashpot pushrods is a thing aside from just a broken pivot. And this seems to have nothing to do with carbon in the intake or on the swirl valves.

2) General lubrication of the linkage joints - and this one probably combines with #1 anyway. I could speculate that the silent P2004 is really saying that the swirl valves are taking too long to return to their open position (or maybe hanging just enough so both hall effect switches don't close). This would be the likely situation that Jenn's car may be in. At 104k not sure if I suspect a massive intake carbon issue (aside from the lady's very gentle right foot). What if the linkage just gets stiff and the response is a bit slow? With no REAL drivability symptoms and a silent code, this seems more like Jenn's scenario. However, this will just worsen with time until something breaks and presumably you get the rest of the codes since the system becomes totally unresponsive and you get a CEL. These people said this has been there for a long time which isn't great but maybe it's not too late. The solution would be to lubricate the linkage and exercise the system.

3) Actual intake carbon causing the swirl valves to physically lock up. This is the scary use case because replacing the pivot and pushrod with a stronger part will likely lead to breaking off a swirl valve and hanging an intake valve open. This seems more like a high mileage situation to me and also more likely if the crankcase breather system has not been maintained (centrifuge cover, et al). I think this is MORE common than it was due to age/mileage of M272 vehicles but I am now convinced that this is NOT the singular (or even the most common) failure mode.

I am leaning toward #2 for Jenn's car given all the data I have. I don't know if an occasional Seafoam type treatment is a good idea or even effective at cleaning the intake. I would think that there is a mileage where you just need to replace the damn intake manifold but given maintenance of the oil separation system and lubricating the swirl valve linkages, this should be comfortably "high" like 200k+, ideally.

I do think that if swirl valve carbon is suspected (i.e. they don't move freely between stops), pulling the intake and at least attempting a clean of each valve is prudent.

Looks like it was probably #1? Pivot is broken but the swirl valves operate freely. It could still be a lubrication issue right at the pivot (or the pivot itself) but all of the swirl valves and their linkage didn't seem to be binding. Adam said they just zip tied the swirl valves open until they feel like dealing with this. He said they bought this kit:
https://mercedessource.com/store/m272-v ... or-upgrade

I like the idea of giving Kent business and the price is really perfectly fair for what the kit comes with, plus a paywall video.