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Old 04-23-2009, 11:20 AM   #1
drdolil99
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Default Check Engine Light, CAT or no?

Hi everyone,

I have a check engine light on, on my 2007 2.5. I have 128K miles on it. I have been told it is most likely the cat, but I dont want to spend the money for it.

I am gettiner P0420 on the OBDII reader. I clear the code and the car stalls for a day every time I stop. I want to replace the o2 sensors, I am thinking generic.. is that a bad idea? Does anyone know how many wires are on the o2 sensors so I can get the correct generic replacment?

Also I have been told by some that there is 1 cat and by others that there is 2. Below is diagram of my exhaust. I have been told that item D is what I need, but I think Item C is really what I need. Can anyone help?

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Old 04-23-2009, 12:35 PM   #2
LetItSnow
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Money says you could probably bag either of those items from somebody on the forum; they're getting pulled all the time.
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Old 04-23-2009, 12:38 PM   #3
drdolil99
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The problem is, is that it is a 2.5RS, not a WRX or STI. I have yet to see it. I am hoping your are right though.
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Old 04-23-2009, 02:37 PM   #4
yarrgh
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D is the header, no cats there. C is the cat-pipe section, cats are there. If the car is stalling, your cats may be starting to clog up. How high can you rev the engine when driving? Does it seem like it just won't go over a certain rpm? If you don't want to spend the money to fix your car, we can't help you. If you're concerned about wires, crawl under there and inspect. My front oxygen sensor has 5 wires and the rear has 4. But mine is an 01, so yours may be different.
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Old 04-23-2009, 02:44 PM   #5
drdolil99
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Quote:
Originally Posted by yarrgh View Post
D is the header, no cats there. C is the cat-pipe section, cats are there. If the car is stalling, your cats may be starting to clog up. How high can you rev the engine when driving? Does it seem like it just won't go over a certain rpm? If you don't want to spend the money to fix your car, we can't help you. If you're concerned about wires, crawl under there and inspect. My front oxygen sensor has 5 wires and the rear has 4. But mine is an 01, so yours may be different.
I am not really concerned about spending money, I just dont want this to be a $1500 job. The car seems to run fine, until I turn off the CEL; that's when it stalls. I can rev the engine as high as it will go.

What do you think about generic o2 sensors? I am looking for Bosch ones, but I do not see them for '07s.
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Old 04-23-2009, 02:45 PM   #6
Jerry Xu
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128K on an 07, that is wow lot of miles.
The picture is for RS not for 2.5i.
Generic O2 is fine. But the OEM doesn't cost much more.
P0420 if I remember correctly is Cat efficiency low. Replace the sensor see if the code goes away.
However, this code is for environmental only. Why it would stall the car I don't know.
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Old 04-23-2009, 02:48 PM   #7
drdolil99
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Quote:
Originally Posted by Jerry Xu View Post
128K on an 07, that is wow lot of miles.
The picture is for RS not for 2.5i.
Generic O2 is fine. But the OEM doesn't cost much more.
P0420 if I remember correctly is Cat efficiency low. Replace the sensor see if the code goes away.
However, this code is for environmental only. Why it would stall the car I don't know.
Thanks for the help Jerry! I think I am going to take yarrgh's advice and climb under the car to see how many wires are on the sensor. If you look here I see th o2 sensor for only $35 for a 4 wire sensor; they have other sensors with more or less wires as well:
http://cgi.ebay.com/ebaymotors/OXYGE...1%7C240%3A1318
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Old 04-23-2009, 02:54 PM   #8
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First off that is not the diagram for your car, that is for a 98-05 RS. The 2.5i's changed the exhaust design.

Now I cant tell you exactly what would be wrong with your car but yes a new rear o2 would be a good start. I would NEVER get generic, just go to the dealer and buy a brand new one, you will be much happier and headache free. Main reason being if you put generic in and have the same issue, you cant tell if the issue is from somewhere else or just a crappy sensor you got or how you wired it up, etc
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Old 04-23-2009, 03:01 PM   #9
drdolil99
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Quote:
Originally Posted by piker28 View Post
First off that is not the diagram for your car, that is for a 98-05 RS. The 2.5i's changed the exhaust design.

Now I cant tell you exactly what would be wrong with your car but yes a new rear o2 would be a good start. I would NEVER get generic, just go to the dealer and buy a brand new one, you will be much happier and headache free. Main reason being if you put generic in and have the same issue, you cant tell if the issue is from somewhere else or just a crappy sensor you got or how you wired it up, etc
I got that diagram from www.subarupartsforyou.com when I put in my year and model of the car. Thanks for the insite on getting th OEM sensor. I will pick one up late next week.
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Old 04-23-2009, 03:05 PM   #10
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Strange thing is though, that even with the rear sensor out of whack i do not think it should make the car stall as you said it does. When driving it around does it feel like it has a lack of power or doesnt really rev?
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Old 04-23-2009, 03:07 PM   #11
drdolil99
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Quote:
Originally Posted by piker28 View Post
Strange thing is though, that even with the rear sensor out of whack i do not think it should make the car stall as you said it does. When driving it around does it feel like it has a lack of power or doesnt really rev?
Honestly it drive like it is new to me.. with the exception of the wheel balance that I need. There is absolutely no lack of power or anything.
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Old 04-23-2009, 03:18 PM   #12
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do u seriously have 128,000 mi on a 2yr. old car? it is the cat, but maybe the sensor too. random tech makes a bolt-on replacement for that cat. it is slightly more expensive than dealer, but u get some power with it. good luck.
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Old 04-23-2009, 06:05 PM   #13
smithrcing17
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holy **** dude thats like 64k a year!!!!
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Old 04-23-2009, 08:12 PM   #14
RaceFaceXC
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Quote:
Originally Posted by drdolil99 View Post
Hi everyone,

I have a check engine light on, on my 2007 2.5. I have 128K miles on it. I have been told it is most likely the cat, but I dont want to spend the money for it.

I am gettiner P0420 on the OBDII reader. I clear the code and the car stalls for a day every time I stop. I want to replace the o2 sensors, I am thinking generic.. is that a bad idea? Does anyone know how many wires are on the o2 sensors so I can get the correct generic replacment?

Also I have been told by some that there is 1 cat and by others that there is 2. Below is diagram of my exhaust. I have been told that item D is what I need, but I think Item C is really what I need. Can anyone help?

That is 100% NOT your exhaust system. your system has one cat in the exhaust manifold and a second in the "catpipe". The fact that it drives normally and only stalls when you clear the CEL is evidence that it's the O2 sensor data that is poor/wrong causing the ECU to miscalculate fueling. I would test/replace the front O2 sensor first as its the most likely cause for your CEL and associated problems. This is my educated theory, and not a professional diagnosis but i would put my own money on it.

Quote:
Originally Posted by Jerry Xu View Post
128K on an 07, that is wow lot of miles.
The picture is for RS not for 2.5i.
Generic O2 is fine. But the OEM doesn't cost much more.
P0420 if I remember correctly is Cat efficiency low. Replace the sensor see if the code goes away.
However, this code is for environmental only. Why it would stall the car I don't know.
If it's getting bad data from the O2 sensor it could be miscalculating fueling causing stalling and poor driveability in closed loop. In open loop it wouldnt use O2 sensor input, so a loss of power may not occur.
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Old 04-26-2009, 03:02 PM   #15
drdolil99
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OK Everyone, I used my scan tool and I am getting the following readings on my o2 sensor. the o2 sensor on the front is fluctuating.









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Old 04-27-2009, 12:19 AM   #16
Bluefoton
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+1 on not getting a generic or Bosh 02 sensor. Sure they are cheaper, but a 100$ save asks for troubles from the moment you install it. Symptoms point towards the sensor, as RaceFace said. That'd be the first thing I would change... plus at 130 kmiles, it's not unusual.

..and how the hell you got such a mileage?! Basic maths point to you doing a 130 mile commute every day to work ...
man, you tank daily, change your oil every Friday, and spark plugs monthly??
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Old 04-27-2009, 01:16 PM   #17
drdolil99
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My 5 day commute is 200 miles every day. Exactly 100 each way, plus I drive a lot on the weekends. I fill my take every other day, I have only changed my spark plugs 2 times since I have purchased the car. Last time I put the Bosche Platinum +4 in. They claim to last a long time, so I am taking advantage. I also use full synthetic and change every 4K miles or so.

Quote:
Originally Posted by Bluefoton View Post
+1 on not getting a generic or Bosh 02 sensor. Sure they are cheaper, but a 100$ save asks for troubles from the moment you install it. Symptoms point towards the sensor, as RaceFace said. That'd be the first thing I would change... plus at 130 kmiles, it's not unusual.

..and how the hell you got such a mileage?! Basic maths point to you doing a 130 mile commute every day to work ...
man, you tank daily, change your oil every Friday, and spark plugs monthly??
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Old 04-27-2009, 03:25 PM   #18
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i have a 2007 2.5i and i just did the borla uel header swap. however there is a cat in the headers themselves, the diagram you have on there is NOT the correct one for our cars. the o2 sensors are before and AFTER the cat built in the headers. there's a secondary cat after the headers too! the picture of where the cats are in the diagram is false, thats off an 05 and below rs. it very well could be either issue whether its a cat or o2 sensor. best bet is to bring it to an exhaust shop and have them check it 100% or go to like an advance auto cuz they will tell you which o2 sensor is failing if it not both of them.

good luck buddy.
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Old 04-27-2009, 10:08 PM   #19
watchunglava
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128k on an 07!!!!!!! ftw!!!!!!! you rule dude . where the hell do you drive? i got my 07 in 06 and have 27k!!!!!! you have 100k more wow . i have driven my car across country twice too lol !
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Old 04-28-2009, 12:04 AM   #20
Bluefoton
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Woha. thank god the seats are somewhat comfy, or you'd be doing a daily stop at the chiro.

Off topic, but IMHO you can easily drive 6 000 miles on a synth. oil before changing it (and probably more assuming it's freeway driven). I just hit over 6000 since my last change 3 months ago, and its nowwhere near dark. Highway driving is a blessing for an engine..

Are you changing the O2 soon then?

Quote:
Originally Posted by drdolil99 View Post
My 5 day commute is 200 miles every day. Exactly 100 each way, plus I drive a lot on the weekends. I fill my take every other day, I have only changed my spark plugs 2 times since I have purchased the car. Last time I put the Bosche Platinum +4 in. They claim to last a long time, so I am taking advantage. I also use full synthetic and change every 4K miles or so.
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Old 08-26-2011, 03:47 PM   #21
JetGirlArt
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my 07 2.5i is doing this now at over 100k miles, had the code read and it came up inefficiency in the cat system. but... whats fun, is the light will go away once my tank is below a quarter full. I can fill up, drive around a day or two, then it comes back on.
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