CEL Evap

Anybody know what these could be?
had these since i bought the truck and im wanting to get the check engine light off. not sure where to start on it apart from praying the gas cap does it

 

Get used to these...

As with all automotive diagnostics, troubleshoot LOGICALLY, not because some turd on this forums says: "prolly the cat"

THAT SAID, I know my 2003 pops these codes all the time. Been thru lots of parts, some legit problems, some bad choices based on tinternet "experts: O2 sensors, charcoal canisters, evap solenoids, bad gas, etc. Start with checking all the evap circuit valves- check for operation with a multimeter and a known good 12v power supply. Then move to checking the vacuum lines, even a small leak will give you grief. I eventually had to have a smoke test to get them all. The aftermarket offerings for O2 sensors are not all created equally, buyer beware if you don't' replace with OEM accredited parts here. Is your exhaust in decent shape? I had a leaking joint that got me into some fun rabbit holes.

How many miles? It is very possible the cat is smoked. It also very possible that it's just a dirty sensor and a broken vacuum switch.

 

The P0420 and the P0136 are related. The O2 sensor after the cat is used to determine if the cat is working and this is dependant on a leak free exhaust system.

The evap codes could cause you problems. You are going to have to do your research to find out where the purge valve is and see if it is working... I dont know if there is bi-directional control of the purge valve in an 02 via the scan tool. One thing to remember is that most evap codes are a 2 drive cycle tests and getting the truck in test mode requires a fuel level over 1/4 but not over 3/4 full and for it to sit a minimum of 8 hours AND have the coolant temp be within 10 degrees outside air temp.

 

On my 04 I’ve been getting P0446, P0442, P0441 for years and haven’t been able to really pin point it (did some research but haven’t tried too hard). When I first bought it in 2020, the first time it went off for these was after using seafoam in the gas tank. Idk if it cleared gunk that was keeping things sealed as I’ve heard mixed reviews on using it on an older vehicle if never used before.

I notice when I use 87 gas it happens less or not at all. I was trying to save money and was using 85 and it was going off every month or 2. Went back to 87 mid year and last time the CEL went off for it was June. I’ll prob try to figure it out one day.

 

Pithy... yours sounds like an intermitant sticky/not sealing vent valve. Intermittants are difficult and usually you just replace it rarther than spending shop time chasing it.

 

Have you either checked or tested your MAF or TPS sensors? I started there when my CEL lit up followed by that code. As has been stated in previous posts, the culprit could either be one of the above or a combination any of the aforementioned. Just my two cents, but I'd stay with OEM parts.