Half the time these codes are thrown from a gas cap or filler tube not sealing properly. So start withe easy one and replace the gas cap. Clear your codes. Then if those codes come back, start following the below procedures.
If you can, look at the EVAPPDC PID with a scanner. Turn you your key on engine off. Back probe the EVAP canister signal wire and ground. If the EVAPPDC is at 0% and the voltage is less than 1.0 volts, or if the EVAPPDC is at 100% and the voltage is less than .5 volts you have a problem with the circuit or the actual EVAP valve.
The EVAP canister purge valve is normally closed, and the canister vent solenoid is normally open.
You can rule out the EVAP canister purge valve itself by testing it's electrical resistance. With the motor completely cool, back probe both sides of the EVAP CPV and the resistance should be between 30 and 38 ohms.
To check to see if the EVAP canister purge valve is open (normally closed), back probe the EVAP CPV between the PCM harness connector pin(56) and EVAP CVP harness connector. The resistance should be less than 5 ohms or else the CPV circuit is being help open.
To check to see if the EVAP canister purge valve is shorted to ground, back probe the EVAP CPV between the EVAP CVP harness connector and the negative battery post. If the resistance is more than 10,000 ohms, the CPV circuit is shorted to ground.
To check to see if the EVAP canister purge valve is shorted to power, back probe the EVAP CPV between the EVAP CVP harness connector and the negative battery post. If the voltage is more than 10.5 volts, the CPV circuit is shorted to power.
That's all I can think of right now. I'll check Alldata later to see if I missed anything.
