P0440 in M113 R129 SL500
 

Hello folks,

I have a 2001 SL500 with a recurring P0440 code. I bought two gas caps already and the code continues to return, so I figure it's not the gas cap. Inside the engine bay, the MOT valve looks fairly new to me, so I don't believe it's that either (though can't rule it out).

Engine runs fine, of course. No other codes.

I don't have much/any experience with evap codes... can anyone help steer me in the right direction?

The first step is to get a detailed description of the code and not randomly change parts.

Thanks - I did get a MB mechanic to scan it, and I am aware that it is a code for the evap system. Most common culprit is an old gas cap, which does not appear to be issue here. Another common issue is with the purge valve (000-470-88-93), which looks new/recently replaced.

I'd rather fix this on my own but I'll take it to my mechanic if necessary. Just wondering if anyone else has experience with this code and the repairs associated with it.

The evap system is a close circuit. Any leaky hose will give the code, gas cap is one of the reason. The shop uses a smoke test to find the leak. It is not easy for diy. I fixed it by slightly pressuring the gas tank with compress air and hear for hissing sound. Not easy but I was lucky.

Modern OBD2 systems produce very detailed trouble codes and factory repair manuals detailed test procedures. Look at how large the mandated list is not to mention the manufacturer specific list.

You need to get the detailed description for your code otherwise you are just randomly throwing parts at the car.

On the mechanical side, you might have a small leak , large leak , vent or purge solenoid mechanical problem.

On the electrical side there might be a vent or purge solenoid electrical problem , tank pressure sensor problem.

I always have a poster lookup the detailed descriptions as it shows they are taking an active role in fixing the car and are willing to learn. Don't guess, diagnose.

Thank you, this is helpful.

I like to close the loop on my posts. This turned out to be a faulty MOT valve, which was apparently "recently" replaced. A new one was installed and no more P0440.