I have a 2009 Ranger V6 4.0L with 210k miles that's throwing a P0420 code (Bank 1 Catalytic Converter issue); it also gives me a EVAP system leak detected on my OBD-II scanner. The Bank 1 upstream and downstream O2 sensors appear to have similar waveforms; Bank 2 looks normal (fluctuating wave upstream and steady value downstream). The long term fuel trim seems to be a little high, around + 4-7%. There are no performance issues that I notice.

Previously I had a P0132 code. I changed all 6 sparkplugs myself, which were a little overdue for changing. After resetting the CEL, it stayed off for about 2,500 miles and I thought problem solved! Then the CEL came back on and read the P0132 code again. I looked for a faulty wire, found none, so I replaced the upstream O2 sensor myself. No luck. I inspected the wires more carefully and found a faulty ground wire. I patched that with electrical tape and reset the check engine light. A few hundred miles later, I got the P0420 code.

Is my cat bad? I don't want to spend hundreds/thousand of dollars for a new one if there's an easier fix or if the cat is not the problem. I've also read that cat's usually don't go bad on their own. Could this mean there is something causing the cat to fail? I live in PA and have emissions inspection :( which the vehicle will not pass if the CEL is on.

Are there any other tests I can do (myself or a mechanic) to further diagnose the cause of the CEL? Any advice is much appreciated! Thank you for your time!

 

Welcome to the forum

Great diagnoses and testing skills

The downstream O2 should show .7 to .8volts after engine and Cat warm up, should be steady might change now and then as computer adds more fuel to keep Cats hot, but steady other wise

O2 sensors see Oxygen in the exhaust
0.1volt means high oxygen in exhaust, "lean"
0.9v means low oxygen in exhaust, "rich"

The upstream sensors should bounce around very fast between .2 and .6, or so, as computer changes injector open times, sweet spot is .4
After exhaust passes thru the HOT Cat converter the oxygen should have been mostly burn up in the process of cleaning exhaust gases
So steady volts .7-.8, low oxygen at downstream O2

If Cat is not working well then oxygen is not burned up so downstream volts would be lower and jump around similar to upstream because its "seeing" the same exhaust, uncleaned

Not sure what other tests you can do, if you look at upstream and downstream O2s and both are jumping around I would say Cat is not working to burn up the oxygen

An exhaust leak after Cat(or IN Cat) and before downstream O2 will suck in oxygen, but would expect a steady lower voltage not much jumping around
And although its a rare failure an O2 sensor can allow oxygen to leak in around it causing same effect

Yes, burning coolant or oil in the engine can cause Cats to fail early, but it has to be long term, a few months wouldn't cause that much damage

A shop with "sniffer" in the tail pipe can confirm if exhaust is "dirty", failed Cat
2009 Ranger, so 11 year old Cats should not fail, but.............could have been bad from the factory, made on a Friday afternoon before a long weekend, lol, sorry couldn't resist