O2 Sensor Replace

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I was wondering if anyone has replaced their O2 sensors, my upstream O2 is bad and my downstream one is throwing a code saying its going bad.

I've spotted one of the sensors through the engine bay and I'm pretty sure its the downsteam, it looks like its right on the cat. Where is the upstream sensor and easiest way to access it?

BTW 2003 N/A if that makes a difference

Thanks in advance

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you're killing me here

[Sabber]

you could try doing searches for people that have don it to their legacy. should at the vey leats give you an idea.

Try this place. I have found some good info there.
http://legacygt.com

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I was just outside looking at my car and found it, its on the cat at the front end of the car. Open your hood, look from the passanger side down the engine beneath the intake and its the yellow wire.... Oh I just can't wait to try and get it off this weekend (assuming my replacement arrives by then)

[Sabber]

If you can, take pictures. Ive seen this come up a lot and it would be nice to have a walkthrough for people to look at.

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I think I can get a picture taken. I lifted my car just to see if I could get a 22mm wrench in their, I ended up getting a slight burn off the Cat. I guess I'm gonna have to find the specialty 02 Sensor Socket head and I'm as sure as heck going to have to let the car cool off.


The funny thing is the CEL has turned on and off three times now, I found the harness and took a look at. It seems like its working fine running smooth, I wonder if it was a bad connection, maybe a broken wire in the harness.

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Well I've found a few sockets....



now I'll have to guess which one will work best and hope it works so I don't have to buy another one.

[speedymatt]

i cant remember where i posted my issuses with the o2 sensors but here's how it played out.
i started getting an intermittent cel about the front bank, which is the front sensor going bad (the one your referencing). i bought a replacement and didn't have the tools to do it (either the first or third pictured tools would have worked) so i paid a friend at a local shop to install it. the car ran great for a while then the cel came back with a horrible rattle. i researched it and the result was a bad front cat, the dumb part is that the front and rear cats are together on one pipe section so both had to be replaced. i called the dealer for a price and in talking with the parts guy it was discovered that since my baja was under 80k it was covered under warrenty even though i didn't buy it from them and i wasn't the original owner. so i got a $700 part for free.
mine is also an 03 and is doing just fine now.
good luck hopefully it is just the front sensor.

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So if I take it to the dealer will they be able to diagnose the bad Cat or do I have to wait for it to get worse?

[speedymatt]

the dealer should be able to tell you which it is. even after i explained the situation and that i have confirmed (i tapped on the cat and heard it rattle) what the problem was, the dealership still wanted the car for a day to run tests on it. beware that unless its covered under warrenty they will probably want to hit you with a diagnosis charge.

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Major P.I.T.A. I'd strongly suggest the third O2 sensor socket pictured... I picked up a simular style from Advance Auto Parts and its the one I ended up using... about halfway through taking the sensor off I gave up and ran to napa in hopes to get the third socket pictured... they didn't that one, so I went to Auto Zone in frustration and bought their socket which was picture #2 hoping the 8 point wrench point would be helpful... it wasn't I think #3 would be the most helpful with the wench mount on the end.

[davecoon13]

Driving home form work yesterday, the Check Engine Light came on.

I have 61,888 miles--just out of the 6 year/60K 'Added Security' warranty which I paid all that money for that covered nothing.

I have a USB OBDII Code Reader, so I hooked up my laptop and I think I remember that I got the code of "oxygen sensor heater circuit malfunction bank 1 sensor 1"

I have the 2003 Naturally Aspirated Baja. Is this the sensor on the firewall or physically where is this sensor located?

Most of the Auto Parts Stores around here want $170 for the 'UPSTREAM' Sensor. Is this the 'Upstream' Sensor?

I reset the CEL and it did not come on again.

Is this the sensor which controls the fuel metering or just the sensor after the CAT Converter?

If I drive down the road with the laptop hooked up, it monitors the sensor voltage. I think I can set it to log this info or have my wife monitor the screen.

What is the correct voltage? I have heard that the voltage reading will tell you if it is a wiring short or a sensor malfunction, but what voltage indicates which condition?

Now that I reset the CEL and cleared the codes, I am hesitant to replace the O2 sensor until the light comes on again in case I am mis-remembering the code. I don't want to replace the wrong one.

I spoke to the mechanic about this. The CEL went off Thursday when it was cold and rainy out after I took the car out of the heated dry parking structure at work. The mechanic said sometimes a sudden change in both temperature and humidity can trick the Mass Airflow Sensor into sending a signal to the O2 Sensor that more fuel is needed. The laptop did indicate a "rich" fuel mixture when hooked to the OBD2. The Mechanic said if I reset the CEL and it hasn't come back not to worry about this until the CEL goes off again. Does this explanation make sense to you techies out there?

Is it correct that the NA baja has only 2 sensors? I think the Mechanic said there are 2 sensors before the CAT and one after the CAT on that car, does that make sense?

UPDATE: Today CEL came on again, this time with a code of P0030. I just took the car in to have the O2 Sensor replaced tomorrow while I am at work (my wife uses the Metrorail to get to work so her car is idle most days), so I will take my wife's car to work.