CHECK FUEL CAP, TIGHTEN FUEL CAP MESSAGES
This article applies to 05-06 Accords, 06 Civics, 05-06 CRV's 05-06 Elements, 05-06 Odysseys, 05-06 Pilots, 06 Ridgelines and 06 S2000s.
"If a vehicle's fuel fill cap is loose or missing, and the ECM/PCM detects an EVAP system leak when it runs the EVAP monitor, the CHECK FUEL CAP message appears on the information display when the engine is started. A temporary DTC is also stored in the ECM/PCM's memory. If this happens, there's really no need for the owner to bring the vehicle in for service. All he or she has to do is shut off the engine and make sure the fuel fill cap is in place and it's properly tightened.
Although the owner can cycle the message from the display with the reset button, the temporary DTC that's setting the message is still there. This means the message never really goes away. It can be cycled back with the reset button and it comes on again if the ignition switch is cycled or the engine is restarted. This message keeps coming back until the EVAP monitor runs again and it finds no EVAP system leak. This could take several days, even weeks, depending on how often the vehicle is driven.
If, when the next EVAP monitor runs, the cap wasn't tightened or there's another EVAP system leak detected, the MIL comes on and the message goes off. A permanent DTC is now stored in the ECM/PCM's memory. If the owner now tightens the cap, the MIL should go off after the next EVAP monitor run, yet this could still take days or weeks. If the MIL is still on after that monitor run, then it's time to bring the vehicle in for service.
If the vehicle comes into your shop with the fuel cap messaage or the MIL on. make sure the fuel fill cap is in place and properly tightened. Record the DTC, then clear it with the HDS and run the EVAP system function test. If there's still a problem, press on with normal troubleshooting."