How to fix daignostic codes p0304, p0421 and p0455 efficiently without costing an arm and a leg.

Question edited for clarity. P codes for DTCs must have upper case P.

All questions need FULL 'year make model'.

White smoke is steam, and this is normal at this time of year and is mentioned on this website a LOT at this time of year. Gasoline has weather in it at molecular level and is burned off as steam.

P0300 unknown random misfire
P0303 Misfire on Cylinder 3
P0304 As above on 4

OBD-II Trouble Code - P0455

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OBD-II code P0455 is a problem with an Evaporative Emission Control System Leak. Get expert information on fault code P0455.

P0455 Code: Evaporative Emission Control System Large ...

CarParts.com https://www.carparts.com > ... > OBD-II Trouble Codes
Aug 6, 2023 - Code P0455 is typically triggered when your vehicle's computer detects a large leak in the EVAP system. Symptoms of a P0455 include a lit check ... Videos

2:20
How to Fix P0455 Engine Code in 3 Minutes [2 DIY Methods ...
YouTube · nonda 2 minutes, 20 seconds
Oct 21, 2020

Needs a cat and need to check the injector and coil. Coil most common on that model

C1201 error code means that you have some problem in engine control system.

Possible causes for P0421 error

• Warm Up Three Way Catalytic converter deterioration or malfunction
• Exhaust system leaks
• Loose front or rear HO2Ss
• Faulty front heater O2 sensor
• O2 sensors harness is open or shorted
• O2 sensors poor electrical connection

The P0421 code means that the vehicle's control module has detected that the three-way catalytic converter is not working properly (is not as efficient as the factory is expecting). Replacing the oxygen (O2) sensors may sometimes fix the code, but in most cases the catalytic convert needs to be replaced to fix the problem.

P0305 - Cylinder number 5 misfire detected.
Probable faults and reasons:
Igniter no. 5 defective.
Ignition system malfunction.
Spark plug is short or its air too wide. (0.9 - 1.1 mm)
Weak compression.
Valve clearance less than recommended.
Engine valves and seats defective.
Fuel pump pressure too high.
P0421 - Warm up catalytic efficiency is below threshold (Bank 1)
Probable faults and reasons:
Catalytic converter.
Heated oxygen Bank 1.sensor 1, 2.
P1818 - Manufacturer specific code.

Start with a tune up and change your fuel filter. Check your plug wires or better, replace them. The p0421 code has to do with the cat. Also, install spark plug anti foulers, you can get them at your local auto parts store. Follow the spark plug link. As for p1818, have this code reset at a reliable shop preferably a transmission shop. Ask around and some of your friends for their recommendations as to where you can take your car to to have the trans control module reset without the shop trying to tell you you have to fix something, ie shell out the big bucks. tell them aLl you want is to have the code and trans reset, NOTHING MORE. Sometimes this code comes up false. so have it reset after you take care of the tune up etc. this code should be reset using a transmission code reader.

P0421 code is that the cat. converter is below efficiency. 99 per cent o the time the cat. needs to be changed. but if you have a scan tool watch both bank 1 O2 sensor 1 and bank 1 sensor 2.
cold they should be almost the smae but when its at operating temp, and running down the road at crusie speed the frt o2 should switch rapidly between .150 mv. and .850 mv. and the rear o2 should read about .600 mv. if they read the same the cat is ng and will have to be replaced.

P0421: Warm Up Catalyst Efficiency Below Threshold (Bank 1).

This could apear because of a bad O2 sensor on the catalytic converter on bank 1.

Or The catalytic converter is no longer functioning properly.

Hope this helps you. Good luck bro

po421 warm up catalyst efficiency below threshhold bank 1, 431 same on bank 2..

P0031 - most likely pointing to a failed O2 sensor (bank 1 sensor 1 is located before the catalytic converter)

P0421 - failed catalytic converter or a failed O2 sensor

P1512 - intake manifold shutter valve is stuck - may be caused by the O2 sensor, but may not

I recommend replacing your O2 sensor first and see what happens