P0420 Solved for now

[cardoc]

Originally Posted by RedGeminiPA

Mine finally popped up again last night after being out for almost a month since last clearing. I just pulled freeze frame data:

Fuel Sys 1 CL
Fuel Sys 2 CL
Calc Load (%) 22.4
ECT(ºF) 190
STFT B1 (%) -3.9
LTFT B1 (%) 9.4
STFT B2 (%) -3.9
LTFT B2 (%) 7.8
MAP(inHg) 18.3
Eng RPM 2105
Veh Speed (mph) 57

I should note: I was out of town over the weekend, and I got gas from a "Bob's Quick Mart" or something like that, but the light didn't pop up until I was nearing the end of that gas, a little before the low fuel light came on.

We don't have many choices around here for tier 1 gas. There's a Sunoco station about 5 miles away, but the rest around here is typically Sheetz (a huge monopoly of a station in my town), and they're known for using the cheapest gas they can buy.

The ECM is adding a lot of fuel. Too much. You were apparently at light throttle given the MAP reading, speed and rpm. If the station you got your fuel adds a lot of alcohol, that could be the issue. Alcohol goes to the bottom of the tank.

Could be a vacuum leak, but doubtful.

[RedGeminiPA]

Any other ideas what it could be?

I went to my usual station (Sheetz) yesterday and put in about 5 gallons of premium. Light is still on so far.

[RedGeminiPA]

As of this morning, the light is off. I put another $20 of premium in it. We'll see how it goes.

[Kalamen]

I believe that P2096 and P0420 can both be caused by an exhaust leak, is that actually the case. Since I am getting both of those codes, maybe it is coming down to an exhaust leak. If so, would the leak that it is being picked up just be between the 1st and 2nd o2 sensors? I was going to set my shopvac in blow mode, put it in the exhaust and plug the other tailpipe.

[cardoc]

The shop vac trick would work. You will also be pushing air into the engine via the open exhaust valves so you will hear the air moving at the engine, but should be able to find if there is a leak in the exhaust pipe.

[Kalamen]

I couldn't find any exhaust leaks, so back to square 1. I am thinking of getting a oxygen sensor simulator for use on the rear 02 sensor. I have a 08 Outback with PZEV. I watched this video and was going to get one from him, but a comment said the voltage for the rear o2 sensor needs to be .65v or less for PZEV vehicles, and his stimulator runs at .9v. He said he could modify it to the .65v prior to shipping it out, but does anybody know if the rear o2 sensor does in fact need to read .65v or less on pzev vehicles?

OBDII Oxygen Sensor Simulator - YouTube

OBDII Oxygen Sensor Simulator - YouTube

Thanks again for all the input on this one!

[cardoc]

Find what the problem is that is making it lean and repair it. If its a vacuum leak, it changes the combustion and performance. If its the AF sensor, that helps with fuel trims. If its the CAT, well, it won't reburn the HCs or it will clog up depending on what its doing.

[Foldsct]

Well, our '03 subie that we've had for 2 weeks or so and put on about 300 miles had the CEL come on last nite.

Yep, I flipped out. Got it read today and it IS the P0420 that you talk about here.

What should we do first? We've put in 2 full tanks of premium gas, the second one today, because it was running really rough when we got it--probably indicative of crappy gas. It's running better, but not perfect. Also threw in some fuel injector cleaner--recommended by the place we had it read at.

Now where do we go from here? Do we do the PCV valve? I've read a lot of threads, but no one says what to do in what order.....

Help!! Thanks!!!

Elle

[dralb]

Originally Posted by Foldsct

Well, our '03 subie that we've had for 2 weeks or so and put on about 300 miles had the CEL come on last nite.

Yep, I flipped out. Got it read today and it IS the P0420 that you talk about here.

What should we do first? We've put in 2 full tanks of premium gas, the second one today, because it was running really rough when we got it--probably indicative of crappy gas. It's running better, but not perfect. Also threw in some fuel injector cleaner--recommended by the place we had it read at.

Now where do we go from here? Do we do the PCV valve? I've read a lot of threads, but no one says what to do in what order.....

Help!! Thanks!!!

Elle

I would start with the maintenance stuff first. Air filter, oil change, clean/replace PCV valve, plugs, t-stat etc. Depending on when any of that has already been done. To me, it is the best course of action as all those items would need to be done eventually, so it isn't really wasted money. Without having the car hooked up to a scanner and seeing what everything is doing, it is hard to pin it down. You also need to factor in other symptoms and conditions that may point to the culprit(s).

[Foldsct]

Originally Posted by dralb

I would start with the maintenance stuff first. Air filter, oil change, clean/replace PCV valve, plugs, t-stat etc. Depending on when any of that has already been done. To me, it is the best course of action as all those items would need to be done eventually, so it isn't really wasted money. Without having the car hooked up to a scanner and seeing what everything is doing, it is hard to pin it down. You also need to factor in other symptoms and conditions that may point to the culprit(s).

We know it had an oil change JUST before we got it....air filter is clean.

PCV valve is next.

Stupid question. Where is it? We can't find it.......and is it better to replace than clean?

Other than that, we don't know about the maintenance. But we will when it's all fixed......