How do you clear a code on a 1996 3100 buick century

Have code's check ,do the diagnostic's , repair the problem ,then the light will go out .

fan 1 and 2 relay, and the 1655 is evap purge solenoid, the fan relays going bad can cause the car to run hot or overheat, check for broken vacuum lines and replace the purge solenoid if needed.

1994 should be obd1 so disconnect battery for a couple minutes and reconnect

12 means all clear itll flash this this 3 times then try 2 find stored codes

What size engine?

take it back to your mechanic and have him check it again, he may have missed something, or it has more wrong with it than he found on that visit.

Disconnect the battery. If light comes back take to shop to read Diagnostic Trouble Codes.

P0440 is a EVAP leak detected, try changing the gas cap and reseting the ECM to clear the service engine light. If you can not clear the code it takes about three start up with out any issues to clear the code and after 100 start up's the codes will clear from the ECM's history. Note use the GM OEM gas cap for a replacement, anything else is just garbage and you'll be replacing it again with in 6 months. If it's not the gas cap, need to take it to a garage and have them do a smoke test to locate the leak in the system. Good luck and hope this helps, keep me posted. be glad to help

If there was a leak at the gas cap. EG: Left off or loose after fill up? You will need to have the codes cleared or it will clear itself after enough key cycles. EG: Started and shut back off as many as 20 to 50 or more times.

code is evap system flow during non-purge
check the hoses for holes or broken disconnected hoses also check the fuel cap emissions diagram under the hood will give u the location of the evep purge solenoid if all checks ok then replace the soienoid and clear the codes
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