Yesterday my BMW check engine light was on and I did not know what’s going on. I had to limp my vehicle to the nearby parking lot (about 2 miles). I am just to state the problem and share the solution.
Vehicle model: BMW 3 series 2.0L 320i Sedan; 228,000 km
Problem: Check engine light on
Symptom: No noticeable symptom apart from CEL on
Equipment: BMW Scanner 2.0.1
After scanned full ECUs of my BMW computer with a BMW scan tool, I got “P0456” fault code. I phoned my mechanic, an experienced old repairman for solution. He confirmed something wrong with my Evaporative Emissions System (short as EVAP below). He explained me the P0456 code may cause by loose cap, faulty gas cap, or fill the fuel tank while engine running. Then he listed some possible positions for the EVAP system failure:
a small leak in EVAP hose
b. small leak in the vent valve
c. small leak in EVAP canister
Using my BMW scanner to activate the vent, and then monitor the fuel tank pressure sensor. If there are not problem of them and the EVAP system still leak slowly. Use a smoke machine and watch for smoke to check the system at any EVAP system. But remember not to press the EVAP system with air pressure otherwise will damage the system.
Hope it will help those who meet the same occasion.