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Discussion Starter #1
My mustang had the check engine light on. The code was P-0135 which is for the oxygen sensor, as far as I know it is drivers side front. Changed it today. Light went out. Drove to motor vehicles, was told that they couldn't inspect as my computer hadn't fully reset yet.
Started driving home, 20 miles later check engine light came on. Went to Autozone, first they pulled code, same code as before. Then they cleared the code as their belief as well as service mgr at local dealership was it simply hadn't cleared. Code clear, drove 30 miles light back on.
BTW- when the light comes on I think you can feel performance drop a tiny bit and I swear that occasionally I can smell a bad smell rem. of cat converter. Had cats looked at. They seem ok, plus alot of money if it's not needed. They don't seem to glow or get too hot.
Could the o2 i put in be bad? Could I have changed the wrong one? Could there actually be a prob with cat conv. with no codes for it. Autozone mech suggests that sometimes 02 code comes up when something before the 02 sensor is bad not the actual sensor.
Is there a way to test the 02 sensors.
Thanks guys. You've always been a great help.
 

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Try swapping just the harness from the one you changed to the other side and see if the code follows it. If the code stays on that side then it's not the O2, it's probably the Cat. I feel your pain on the inspection, I went through the exact same ordeal a couple weeks ago. Do you have the stock midpipe on your car?
 

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i'm not the original owner but as far as I know the exhaust is all stock. Could the cat cause the same ? Original exhaust how many cats are on here? I thought 2 but now i'm not sure. I can't afford to change it all now so i'm sure hoping it's only one, at least to get thru inspection.
Would it also follow that it would be a cat on the same side?
Next question will be best price on cats.
I truly hate NJ's emission inspection.
 

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Yes, if the catalytic converters are going bad then you could get a check engine light to tell you their efficiency is low and they need to be changed. From the factory the car had 4 catalytic converters. Some people, such as myself have changed to catted midpipes and still have issues with check engine lights. A set of MIL eliminators will eliminate those issues as long as it's the high flow, low efficiency cats giving the problem and not OEM cats that are going bad.
 

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Discussion Starter #5
\Yes, if the catalytic converters are going bad then you could get a check engine light to tell you their efficiency is low and they need to be changed

But wouldn't I get the code that specifies cat converter and not one pointing to o2 sensor? And if i'd get the P0135 code would that mean it's the cat on the driver's side.
What would be the cost to go with the catted midpipes and mil eliminators as opposed to replacing the cat that's causing the problem or all four cats if necessary? Would that effect getting thru nj's emmission pita? I'm assuming you pick up power by getting rid of the current cat system.
 

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I can't say for sure about NJ's emissions because I've never dealt with it. Catted mid pipes go from as low as $250 and all the way up as far as you care to go. Replacing a cat will cost at least 130 or so by the time it's welded in. MIL eliminators run 60-90 bucks also.
 
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You said you changed out your front O2 sensor. That wouldn't read a bad cat. The rear one would go on if it were a bad cat. The code could be different too. It would say catalyse(spelling?) efficiency low or something to that respect.
 

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Discussion Starter #8
You said you changed out your front O2 sensor. That wouldn't read a bad cat. The rear one would go on if it were a bad cat. The code could be different too. It would say catalyse(spelling?) efficiency low or something to that respect.
That's what I thought. So does that have to mean the o2 sensor is still bad, or something leading to it? Any thoughts on where to look for the problem. When I first put the o2 sensor on is when I noticed a bit of smell similar to a bad cat. That smell is gone now. It only happened for like 15 minutes and I could have been mistaken. Also at the same time because of going thru inspection I had put a tank of plus into the car. She's not used to that.
 
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I would go to your local parts shop and see if the upstream O2's are interchangeable, then swap em and see if the code changes... Maybe the people giving you the information misread the code reader and you got the wrong sensor... I've found that the people that work for autozone aren't the most skilled. Some are, but most people are there for a paycheck.
 

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I agree with Matt. Except try just swapping the plugs instead of the entire sensor. As far as I know the plugs are interchangable. If the code moves with the swap, then it's the sensor.
 

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Discussion Starter #11
i rented the tool to pull the o2 sensore from autozone and took it back when everything seemed to be going well. I'm going to have to pick it up tomorrow again.
It was definitely the right code. It's the same one that came up at inspection. I also had another code indicating the purge solenoid needed to be changed. Changed that and that code cleared right away and never came back. So all is well with the computer. As far as I know the upstream sensors are interchangeable. I don't think the plugs will reach from one to the other though so i'd likely have to swap everything. The one will reach so I can see if I end up with two codes by unhooking the one and connecting the other.
Given that I feel sure I have the right code I have to figure I got a bad sensor or the problem is something leading to the sensor that wouldn't trigger a code on it's own. Is it possible that there could be a short leading to the o2 sensor causing it to not function properly?
 
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BlueStreak03 said:
I agree with Matt. Except try just swapping the plugs instead of the entire sensor. As far as I know the plugs are interchangable. If the code moves with the swap, then it's the sensor.
That's a good idea except sometimes the sensors are not interchangeable because the plug for the harness/sensor is different. Which could mean they can't be swapped. Also, I don't know if they will reach. That would be cool if they did. That's why I said check to see if they are all the same O2 sensor part number before you attept that... It'll save you some time and the hassle of crawling underneath the car for nothing.

It could be a wire worn threw causing a short also... Check to see if any wires are hitting the pipes or manifold. That would definitly cause you to throw the code again. Maybe on install you didn't tuck the wires in enough.
 
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