Have a 2003 Volvo S40 turbo that runs great. Check engine light will come on after reset and stay on.The gas cap is tight, wiring harness and spark plugs are new and new timing belt installed. when checked the computer shows no codes or lists any problems.The light is always yellow and has never been red.

SOURCE: Replace the ignition coils on my 2003 Volvo S40

its easy do thiers 4 of them thy push on to ur spark plugs 2 scews hold them in place disconect the leeds going on to the coil one by one then pull out and put in ur new one's

SOURCE: Check engine light/gas cap will not stay tight.

yes the gas cap could cause this,also check evap. purge solenoid and hoses for cracks or kinks,the solenoid is on the inner fender and has 2 hoses, one to the intake and one to the canister, the most common cause of this code is a defective purge solenoid.

SOURCE: location of volvo s40 2003 oil filter

It is underneath near the oil pan. Not really a filter, but the cover to the filter. Should be a black round looking thing. Remove this, and the paper filter element is inside. Be careful not to crack or damage the cover.

SOURCE: Oil Leaking into the exhaust

hi there, there are chemicals on the market that will soften up the seals but these take time to work i would suggest changing the turbo, you will also have to remove the oil from the exhaust system this can be done with other chemicals like an upper cylinder cleaner feed directly in to the air intake but only after the turbo has be fixed
Regards JR

SOURCE: belt routing diagram 2001 volvo s40 1.9l turbo