Recently, my check engine light is on. I've pulled out the codes and they're 0304, 0705, and 0903. I know the first code is relate to ks and I saw Daniel Martin posted the informative message about how to fix it. But for the last 2, I have no idea. Could someone let me know how to diagnose and fix it.
Thanks

 

...just personal message Daniel B.

 

Diagnostic Trouble Code 0705 points to a problem with the Evaporative Emission Control System.

This malfunction is detected when the EVAP control system has a leak or the EVAP control system does not operate properly. (EVAP = EVAPorative emissions.)
Possible causes include...
- incorrect fuel tank vacuum relief valve
- incorrect fuel filler cap
- fuel filler cap vent remains open or fails to close
- foreign matter caught in fuel filler cap
- a leak in the line between the intake manifold and the
EVAP Canister Vacuum Control Valve
- foreign matter caught in the EVAP CVCV
- leaks in the EVAP canister or fuel tank
- leaks in the EVAP purge line (pipe and rubber tube)
- EVAP purge line rubber tube bent
- blocked or bent rubber tube to EVAP control system pressure sensor
- loose or disconnected rubber tube
- EVAP CVCV and circuit
- EVAP Canister Purge Volume Control Solenoid Valve and circuit
- absolute pressure sensor
- tank fuel temperature sensor
- MAP/BARO switch solenoid valve and circuit
- blocked or bent rubber tube to MAP/BARO switch solenoid valve
- O-ring of EVAP CVCV is missing or damaged
- water separator
- EVAP canister saturated with water
- EVAP control system pressure sensor
- refueling EVAP vapor cut valve
- ORVR system leaks

This is a "jackpot" code. It points to so many possible causes as to be almost useless. It may be accompanied by another DTC which is more specific.

 

Diagnostic Trouble Code 0903 points to a problem with the EVAP Canister Vent Control Valve. EVAP = EVAPorative emissions control system. This is the system which seeks to minimize air pollution which results from evaporation (as opposed to incomplete combustion) of gasoline.

The EVAP CVCV is located on the EVAP canister (underneath the vehicle near the left rear tire) and is used to seal the canister vent. It has one hose connection and one two-wire electrical connector. The solenoid in the EVAP CVCV responds to signals from the ECM. When the ECM sends an ON signal, the coil in the solenoid valve is energized. A plunger then moves to seal the canister vent. The ability to seal the vent is a necessary part of the diagnosis algorithms for other evaporative loss system components. This solenoid valve is used only for diagnosis, and usually remains open. When the vent is closed, under normal purge conditions, the evaporative loss system is depressurized allowing "EVAP Control System (Small Leak)" diagnosis. Since this part is used only for brief emissions tests the vehicle will usually start and run well despite a Service Engine Soon warning light on the dashboard.

The EVAP CVCV may be bench tested. Remove it from the vehicle (one hose, one connector, two bolts). Verify that air may pass freely through the valve. Then use a pair of fused test leads to apply 12 volts to the terminals to energize the solenoid. Verify that air does not pass freely through the valve. If the CVCV fails these tests, try cleaning it with WD-40 and compressed air. If this fails to free it up, replace the valve. When you install a CVCV (the original or a replacement) always use a new O-ring.

 

Thanks for the info Daniel. I will check it out during the weekend.