I recently just purchased a Chevy 1500 2004 5.3 L V8 it’s got around 105k miles the day or two after I bought it. The check engine light came on so the guy must’ve had cleared before I bought it anyways I win got it put on a computer and I’m getting a random multiple cylinder, misfire, and an evap vent solenoid valve control system code /P0300 and P0446 I changed the plugs and wires and also replaced the vapor canister vent solenoid and the light went off for the day but the next day the check engine light came back on was wondering if anyone else has had this problem or could give me some advice on what to check next id highly appreciate any advice thanks in advance and god bless

 

The first thing you have to understand is that a Diagnostic Trouble Code (DTC) never, ever tells one that a given part or parts are defective. DTCs tell you that there is a problem with a circuit or a system, and the DTC provides a starting point for one to diagnose why the DTC was set.

In the case of the P0300, the DTC is telling you that there is a random misfire occurring and that it has not occurred enough times for the ECM to assign it to a specific engine c
ylinder. Cause of a P0300 could be a worn spark plug or plugs, a flaky ignition coil, a flaky spark plug wire, a bad electrical connection to one or more ignition coils, a clank from something hitting the engine block that is picked up by a flaky knock sensor, a poor electrical connection to one or more fuel injectors, a flaky fuel injector, etc. Your job is to determine what is causing the P0300 by testing various parts and visually inspecting the various wiring mentioned above. It could also be weak valve spring, a burned valve, etc.

In the case of the P0446 DTC, the DTC is telling you that there is a problem with the EVAP system's vent valve control circuit. Hence you need to check the electrical system (wiring) that controls vent valve operation. It does not tell you that the EVAP vent valve is bad and needs to be replaced.

So what do you need in terms of special tools to diagnose what is wrong? Well you will need a decent OBDII code reader/live data scanner, a decent Digital MultiMeter (DMM) and access to a factory type service manual.

Here are a couple of links to online service manuals:

https://mcdowellpubliclibrary.org/chilton-auto-repair/

https://charm.li/

You will be able to find how to diagnose your Silverado's DTCs using either online resource.

Good Luck!