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BMW 740iL P0459 Evaporative Emission System Leak Diagnosis and Fix

Model: BMW 740iL Fault Code: P0455 Posted: 2011-02-14 20:08

The check engine light has been on for several months, intermittently turning off and then returning. An OBD2 scanner (Innova 3100) detected fault code P0455, indicating a large evaporative emission (EVAP) system leak. I have inspected the gas cap, which appears to be secure and properly sealed. No noticeable performance issues have been observed in the vehicle, which is a 1999 BMW 740iL with an automatic transmission. There are minor oil leaks visible, along with a slight power steering fluid leak. On warm or hot days, a loud 'whoosh' or hum noise is heard from underneath the car—difficult to pinpoint exactly but seems to originate near the undercarriage. I am preparing for smog inspection next month and would appreciate advice on potential causes of P0455. The EVAP system may involve issues such as loose hose connections, intake leaks, a failed EVAP canister, or a malfunctioning purge valve. The purge valve is typically located near the oil filter housing (as seen in reference images). While I am unsure of the exact location of the EVAP canister, it is generally found beneath the front wing, behind the wheel arch. Over time, hoses or components may crack due to age and exposure. I have already replaced the gas cap with a new OEM model (two versions available for E38 1999 models; selected the older version based on dealer recommendations). After clearing the code, it has not reappeared during initial use. As per advice from another forum post, I will drive approximately 50 miles before my smog test to ensure stability. Update: The vehicle successfully passed the smog inspection, and the P0455 code has not returned.

Related fault codes
P0455
Comments (4)
Anonymous 2011-02-15 14:00

P0455 indicates a large evaporative emission (EVAP) system leak. Common causes include loose or damaged hoses, intake leaks, EVAP canister failure, or a faulty purge valve. The purge valve is typically located near the oil filter housing. The EVAP canister is often found beneath the front wing, behind the wheel arch. Over time, aging and exposure may cause cracks in hoses or components—inspect these areas carefully.

Anonymous 2011-02-21 01:30

Thanks for the input. I replaced the gas cap with a new OEM unit (both versions available for E38 1999 models; selected the older version). After clearing the code, it has not reappeared. As advised in another thread, I will complete approximately 50 miles of driving before my smog inspection to ensure system stability.

Anonymous 2011-02-28 01:04

Update: The vehicle passed the smog inspection without any recurrence of the P0455 code. This suggests that the issue was likely resolved by the gas cap replacement and/or the EVAP system components are now functioning properly.

Anonymous 2011-02-28 06:14

Great to hear! A successful smog pass with no return of the P0455 code indicates a likely fix—especially if the gas cap and EVAP system were properly addressed. This outcome validates the importance of proper maintenance for older BMW models like the E38 740iL.