Manager Forum

I have a 1999 C280 in my shop that has two DTC's (P0442 & P0450) Usually I would try a fuel cap first - sound reasonable or, with P0450, should I look somewhere else?

I'd disregard the 442 since the 450 is related to the tank pressure sensor. With a malfunctioning sensor, the computer could erroneously see a leak that wasn't there. Concentrate on the 450.

In that case a smoke test is unnecessary at this time, correct?

Forgive me - I am not as familiar with Mercedes as most others. would that sensor have anything to do with the Purge Valve Solenoid?

Mercedes uses the tank pressure sensor to determine leaks. If the sensor is erratic and reading incorrectly, it could confuse that with a leak. I personally wouldn't leak test it initially. I'd test the FTP and see if it's reading correctly and steadily. I do nothing else on an evap system that has an FTP code until I verify FTP operation. Everythng leak-wise depends on it.

The only relation with the purge solenoid is they are within the same system and work in tandem, that's all. My thought is the 442 is false. Of course, you could have multiple issues.

The FTP on this is incorporated with the level sensor. Testing is usually done by drawing a vacuum at the purge solenoid and monitoring the voltage change.

Thanks for the input. I found the sender is faulty. Just to confirm, this would then send false failure code for the Evap sensor. Correct?

it can cause that code. mercedes can overcomplicate (and do) emission systems. the germans wil complicate things. it seems that ric has been lead down the yellow brick road diagnosing these cars before.

steven kiser wrote:it can cause that code. mercedes can overcomplicate (and do) emission systems. the germans wil complicate things. it seems that ric has been lead down the yellow brick road diagnosing these cars before.

Hahaha! Yeah, you could say I learn from my mistakes.

Fix the sensor, then run the evap monitor and check for any pending codes.