I have a 2001 Dodge 2500 4wd,, gas engine,, codes p0138 and p0455 come up,,what do they mean. Thanks

P0138 DODGE - O2 sensor 1/2 Circuit highhttp://engine-codes.com/p0138_dodge.htmlForum CodePossible causes- Rear Heated Oxygen Sensor Bank 1 harness is open or shorted
- Rear Heated Oxygen Sensor Bank 1 circuit poor electrical connection
- Faulty Rear Heated Oxygen Sensor Bank 1
- Inappropriate fuel pressure
- Faulty fuel injectors
- Intake air leaks may be faulty
- Exhaust gas leaks Tech notes Replacing the rear O2 Sensor bank 1 usually takes care of the problem.

this obd2 trouble code table can help you understand the meaning of code.
and for p0455, you can try:

Remove and reinstall the gas cap, clear the codes, and drive for a day and see if the codes come back.

Otherwise, replace the gas cap, and/or

Inspect the EVAP system for cuts/holes in tubes/hoses (you may hear a vacuum noise or smell fuel), repair if necessary

P0442 Means you have a small leak in your EVAP system. P0455 is a large leak.
The EVAP system prevents gas vapors from entering the air .
This code can be set by a leak in the lines or a clogged charcoal canister.
Most common reason is If you did not put your gas cap on all the way.
Hope this helps
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thank you FixYa

This code will not stall or no start of your engine, evap only work when engine is off, it is to reduce the fume your gas tank lets out to protect the o zone, but it will not pass Emission test, also could be some thing a small as your gas cap not sealing right.

Or maybe the recall on the fuel return line 2001 Dodge Stratus Recall Date: 10/27/2000 2001 Dodge Stratus Component: FUEL SYSTEM, GASOLINE:DELIVERY:HOSES, LINES/PIPING, AND FITTINGS Potential Units Affected: 13100
Summary: VEHICLE DESCRIPTION: PASSENGER VEHICLES. THE OUTER LAYER ONLY OF THIS 3-LAYER FUEL RETURN HOSE DOES NOT CONTAIN THE DESIRED OZONE PROTECTION DUE TO A PROCESSING ERROR.
Consequence: THIS HOSE IS CONSIDERED TO BE INADEQUATE.
Remedy: DEALERS WILL REPLACE THE FUEL RETURN HOSE.

P0138 (M). O2 Sensor Circuit High Voltage (Bank 1 Sensor 2) ..... P0307 (M). Cylinder # 7 Misfire. Misfire detected in Cylinder # 7.

this is caused by a large gas vapor leak in the fuel tank, most commonly the gas cap is left loose or defective.

Evaporative Emission System Leak Detected (large leak)
Is the gas cap missing or loose?

P0455 is a EVAP system leak detected code check to make sure your gas cap is tight or if you put gas in it while it was running and can set it . First tighten the gas cap then clear the code and drive and see if the code comes back.

P0442--Evap Emission Sys. leak detected small leak
P0455--Evap Emission sys. leak detected gross leak
P0456--Evap Emission Sys. leak detected very small leak