I have a 2005 Matrix XR with 271K miles that has a CEL that I need extinguished so I can get it to pass emission/inspection. I've checked it multiple times (and reset the computer) and it is usually just a P0420. Today I checked and also saw a P0171.
Details that may or may not be relevant:
- About two years ago I was in the same situation of having a P0420 and needing it extinguished. I was thinking at the time I wouldn't have the car more than 6 more months so I replaced the catalytic converter with a $120 version from ebay and reset the computer. I drove it around until it completed the drive cycles (maybe 1 or 2 days) and then took it immediately to get emissions/inspection. It passed, but less than a week later the light came on, and you guessed it: P0420.
- I push this car hard, and occasionally (for example, at 80mph with the gas pedal floored and engine wound kinda high) there'll be this hesitation which my only slightly-knowledgeable head says is detonation and/or the computer fiddling with the timing as it detects detonation/lean. That could be related to the P0171. This is just a slightly-educated guess, and what I'm getting at here is that the P0171 may be a secondary result of whatever is causing the P0420 (remember, the P0171 isn't always present, but the P0420 is always present).
- I get probably one or two drops of oil when i park it and top off the oil with a quart probably every 2 months. I'm guessing with the small amount of oil that it leaks that I might be burning some oil too, but not enough to be obvious from the exhaust (maybe a year and a half ago I checked and had good compression in every cylinder). I include this because my understanding is that oil can foul O2 sensors and cats.
- I can occasionally smell antifreeze on a hot day after I park it and every two to three months I add a bit of coolant to top it off. I include this because my understanding is that antifreeze can foul O2 sensors and cats.
- My $40 code reader also has "live data" capability. So I can see the voltage levels of both O2 sensors. However, ... I don't know what they should be or how they should bounce around, and also the values only update about once a second and it isn't clear to me if that's fast enough to be useful. Further, it just gives numbers and doesn't plot--not sure if that's what's really needed to useful or not.
I'm thinking of just replacing the O2 sensors and then trying to complete the drive cycle to see if that fixes the issue (pretty sure the P0420 gets set in like 5 minutes, well before all drive cycles are complete). And then if that doesn't take care of the problem then replacing the 2 year old catalytic converter.
Is this a reasonable approach? Too much, too little? I don't currently have an extra car for trips to Autozone/O'Reilly's/Advance Auto and want to have parts I might need on-hand. Anything I might be missing?
Anybody know what I should be seeing with the O2 sensor voltage levels? Or know of a good source you can point me to on that?
Thanks so much,