To add on to the first post, your gas cap may be leaking.
Please refer to the provided links. https://www.autocodes.com/p0456_hyundai.html
https://www.autocodes.com/p0442_hyundai.html
You have a leak in the fuel system or a defective fuel tank and or evap pump or pressure sensor or both
SOURCE: CODES,P0442,P0455,P0456,P1684
Yes, the P1684 on the Chrysler line does not indicate a fault. My sebring had codes p0442 and p0456 both indicating very small evep leaks. When I did the 3 time switch on of the ignition, the odometer readout gave me the p1684 first and then the other two. The scanner at the garage only indicated two "very small evap leaks" one for the second two codes. Clearly the first is a status indicator such as recent battery disconnect or another non problematic indicator. Wouldn't it be great if these manufacturers at least gave you the information to identify what their dummy lights are telling you so you didn't have to go on faith at the garage?
SOURCE: 2003 Mazda MPV trouble codes
check the pcv hose at the back of the intake manifold it often leaks and will cause several idle problems
SOURCE: code P0456,P0455, &P0442
hello po442 ,po455,po456 is leak detected possible, check the gas cap , basicaly you have a leak that is larger than 0.020' and smaller than 0.040' in the gas evaporative system use your nose to find this one thanks
SOURCE: Can not read ecm code for emission check in GA
Normally if you can't get a reading from the ecm the ecm is dead, and goes to default mode meaning it will run ok but is at base timing and won't kick in to closed loop having the 02 sensor controlling fuel and timing, they did this because if the past if the ecm failed the car was a pull toy so you sat on the side of the road so the ecm could be bad. You could have someone do a pin out on the ecm but it would take more time than it would cost to replace the ecm.
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