2005 Mercedes-Benz C-Class check engine light keeps coming on!

mercedes-benz
c-class

#1

Check engine light has come on 8 times in the last 27 months. There is no other evidence that the car is not running properly. Each time I have taken the car to the dealer. The last two times they replaced the purge valve. Any suggestions?


#2

Could you post WHY the CEl has come on? The specific codes in the form of P0XXX

Since I have to guess at the reason, I’d say the code is P0456, small evap system leak. Usually caused by a bad gas cap, leaky purge valve or possibly a leak in one of the lines. The first 2 are easy, the last could be a real bear to find. I’d expect that’s why the dealer hasn’t fixed it.

You might try a cheaper, independent mechanic and be prepared to pay him for his time finding that small leak. Should be cheaper in the long run.


#3

The code has been P0456 every time, except for the first time. The dealer has checked multiple times for evaporator system leaks. Both the “shut off valve for the charcoal canister” and the “purge valve” have been replaced. On other occasions, there has been work done to either software or wiring.

I appreciate your suggestion to try an independent mechanic.


#4

The dealer had the car for two weeks and did extensive testing.They also consulted a person from the national office of Mercedes-Benz. They were not able to find any problem using the smoke test, so they did a vacuum test that revealed a problem with the fuel pump/pressure sensor/pressure sender assembly inside the fuel tank. They replaced this assembly and also replaced the gas cap and gas cap seal. They kept the car for several days in order to run the self-diagnostic software routine that detects any leaks in the vapor recovery system. Apparently this test does not run every time the car is driven.
So far, the check engine light has not come back on.