Matthew Cronin

Hello,
I have a check engine light on. Using my ICarsoft MB2 I show a Po453Evap Emissions System pressure sensor/switch High. Drilling into Live data and plenty of research the sensor shows within the appropriate voltage value at 4VDC but does not modulate or react...engine on/off, gas cap off etc.
That said I have the part and for the life of me can't find its physical location. I can only say it is not under the back seat on the tank heads. I found a video of a tech changing one on a S class....located in the RR wheel well behind the liner on the fuel fill/charcoal canister lines. Lacking any clear info I went there on the C300 but its no go.
This sensor should be above fluid level in the vapor tract as it is measuring the Evap system pressure and not fuel pressure so it shouldn't be immersed in the tank. I suspect I am not the first person to chase this issue and would be grateful for a vector into where the little bugger resides. Any help would be appreciated. Thanks, Matt

Code in question

Live data. Sensor not responding and locked up.

alecmascot

Looks like it measures the pressure in the fuel tank. Item 30 is the p/n you have there.

Matthew Cronin

Alec,
I have the pic as a reference point as well but the physical location is elusive. That sensor should be reading the Evap system pressure as you eluded. Looking at the design of it, it is clearly exterior mounted and likely shouldn't be in direct contact with fuel. I really ripped into the car today. The evap system is pretty busy and based off what I had seen I really expected to find it located in the RR wheel well...safely above standing fuel but no go. I even stripped the cowl and airbox off the engine looking to see if it might be drawing from under the hood. I have taken to tracing harness leads in the vicinity of the fuel tank...stripped the trunk and looked in every nook. Nothing.
At this point I would love to find it not just to fix it but also to take some pics and save the next person some trouble by doing up a how to. Thanks for the reply. Matt

alecmascot

Hi Matt. In your MB 2.0 graphic it refers to the "fuel tank pressure" and in WIS the sensor is tested by pressuring the tank. So I think it must be located in the tank.
This switch is only fitted to the NA cars for their more stringent emission controls,
I just found this : https://www.benzworld.org/threads/co...-help.2239514/
Found it !

Matthew Cronin

Alec,
That’s what I needed Sort of LOL. Your info is invaluable. The MAJOR downside...looks like pulling the fuel tank is a 8 hour job. Pull mufflers, driveshafts, axels, diff, right rear hub. All for a evap sensor that with today’s petroleum and all the alcohol we have in it over here is certain to go. Not sure what I’m going to do but pretty sure that the tank if form fitted to the body enough that I can’t get to it.
Thanks much and I will circle back after I Mull it over. And I thought doing the trans conductor plate was a big job.