Help please

[M7risgood]

2009 Subaru Legacy PZE. Started having little acceleration but you could get it to 45 MPH. Auto zone read code and it was bad CC. then Before I changed that it wouldn’t go over 30 MPH. Changed CC (front one) and still same situation. Then I changed 02 sensor and the AF sensor and still same situation. I changed the oil today and attempted to clean MAF sensor. Reset the computer via unplugging battery, codes are gone, but car still runs the same....... WTH????

[apexi]

So it sounds like you had P0420, but since you said codes, what other codes did you have?

[M7risgood]

I don’t remember exactly but it was the one that listed a few things one being TPS sensor

[apexi]

I'm wondering if it was P2138, which I'm reading can put the car into limp mode. Maybe the electrical connection at the gas pedal, or the pedal itself is no good. If you live somewhere where it snows and whatnot, maybe salt or other junk got in there after 9 years.. The factory service manual probably has specs on how to check the pedal and the drive by wire part on the throttle body, I can try to look them up if you want.

 

http://legacygt.com/forums/showthread.php/annoying-p2138-plz-help-219768.html

 

I'm also sort of wondering about a bad/torn engine ground since you also had another code.. Easy to check. There's one going under the battery to the driver side head, and one on the passenger side under the intake I think. I think there's also one back on the transmission sort of under the airbox, directly behind the throttle body, but I forget.

[NickCawks]

I believe the vast majority of codes put it into limp mode. However he says problem persisted after clearing code.

 

OP you really need to write these things down next time. Troubleshooting which code it may be is unproductive.

 

We can assist you much more by trouble shooting based on a code.

[M7risgood]

I have it written down somewhere I will find out what it was. I’m gonna change the plugs cross my fingers and heck out that pedal

[relative4]

Changing the spark plugs or other random parts is unlikely to fix your problem. Slow down, think, diagnose, and repair. First, if I understand correctly, the car is still in limp mode? If so, you have one or more DTCs present. Either go back to AutoZone and have them read your codes again, and keep the codes in a safe place. Do NOT reset.

 

Once you have your codes, follow the procedures in the 2009 FSM for diagnosing them.

http://people.csail.mit.edu/ilh/vacation/

 

Do yourself a favor and get a $20 OBD scanner so you don't have to rely on AutoZone for this most basic of tasks.

[M7risgood]

Yeah I said forget the plugs. Codes are back and now the AT oil temp light is flashing. Perhaps TPS sensor idk yet gonna go get my neighbors code reader

[M7risgood]

p0700 and p0031

[M7risgood]

P0031 p0700

[ehsnils]

P0700 is the transmission, so you probably have gearbox troubles of some kind. But combined with the O2 sensor that's unrelated then I'd start to check that the grounding strap between engine and chassis is good.

[apexi]

The factory service manual is making me think that your alternator, or battery is the issue. I'm not an electrical expert by any means though, so please don't replace those parts because of what I said. Maybe get them checked though, since it can be done for free.

 

If I'm reading the manual right, if the front oxygen sensor is getting less than 10.9 or 10 volts, it'll throw p0031. If the transmission control module is getting voltages less than 10.9/10, it'll throw p0700. The criteria to throw both codes is the same, low voltages. That's why I'm wondering about your battery and alternator, but I could be wrong, maybe it's just a ground as I mentioned earlier.

 

From what I remember the service manual talks about checking the o2 plug for power, checking grounds, and checking wiring.

[08SpecB_DE]

You need a scanner capable of accessing the Trans in order to receive the correct code. P0700 is a generic transmission fault code.

 

P0031 is a heater circuit code for your af sensor. Rarely, there will be a wiring issue with this code, unless the motor has been out recently or had a major tear-down. If wiring looks good, get a factory air/fuel ratio sensor.

[relative4]

The O2 sensors HAVE to be Denso, especially the upstream. If you bought a different brand, fix that. You can start by puttng the old ones back to verify if there's actually a problem there.

Then, as handsome said, you need a scanner that can read transmission codes.

[apexi]

I'm running a ngk/ntk o2 sensor without any issues. I think a well respected vendor here has actually said he doesn't like o2 Denso sensors because they never last long.

[M7risgood]

So let’s say I replace (the fix) will the car still throw codes and would it need to be reset (ecm) before it run correctly? Or do they clear themselves???

[M7risgood]

Also I’ve heard some people say they just unplug the 02 sensors and I’ve tried that but didn’t help

[M7risgood]

Who’s the vendor with the smoking deals on parts?

[ArmyVetMP]

If you had a Cat Converter issue, how is the rest of the exhaust down stream?

 

I replaced my CC last year with an aftermarket one that went bad on me back in December. When the Aftermarket CC went bad, it completely fucked my midpipe, clogged it right up. Had way too much back pressure which prevented the engine from running as it should. I was on the highway, hit the gas to pass a slower driver and my car refused to speed up. I could get to about 40-45 and the car would go no faster. Replaced the CC with a OEM Subaru one, and replaced the Mid-Pipe on the car. Runs perfect now.

[M7risgood]

Unplugged the egr and both o2 sensors and it runs a lot better but still bugs down. Maybe the back cat is plugged with old honeycomb from the front one???

[ArmyVetMP]

I had to completely replace my Header/CAT (stupid one piece part), and the Mid-pipe. Though I have a 2.5i, so only a single CAT on it and a Resonator on the mid-pipe. When my CAT went bad it plugged the mid-pipe. I had to replace both the Header/CAT and the Mid-Pipe before my car ran normally again.