O2 sensors

**Poil336** · 06-26-2009

the service engine light came on awhile ago and it gave off a code for an O2 sensor. it wasn't mine yet so i didn't think anything of it, but i looked for the part recently and search results came back for sensors before the catalytic converter and a different one the goes after the cat. are there actually 2 of them? i imagine there would be different codes if there was more than one, but i've had it read twice and neither guy could give me a definite answer. i haven't really looked for it, so i thought i should start here. any advice would be a great help. it's a naturally aspirated series II 3800 in a 99 gt. also, it gave a code for a mass air flow sensor when i had it read today as well, would a new O2 sensor fix that or am i have to buy both parts?

**JoshMcMadMac** · 06-26-2009

With the age of the vehicle, changing both O2 sensors is just good routine maintenance at this point. Hit them both with Kroil a few times for a few days prior, and get an O2 sensor socket to get them out. sparkplugs.com usually has some of the best prices, and rockauto.com is not far behind. Go with NGK or Denso over Bosch, though.

**Poil336** · 06-27-2009

that probably is a good idea. any tips as to how to find them? like i said, i haven't had the chance to look for them. and the mass air flow sensor, i heard they can be cleaned? i know i'm asking a lot but i'm looking to have this car for awhile and it's been somewhat neglected as far as general maintenance goes, so i'm trying to get it all taken care of now

**JoshMcMadMac** · 06-27-2009

Are you familiar with what they look like? If so, that helps ease locating them. One is down on the exhaust. Get under the car, and you will see it screwed in towards the front half of the vehicle. The other is on the back side of the engine. You will want to roll the engine forward a bit, and even then it is tough to get to. Have extensions handy, and even a breaker-bar to use not only for leverage, but also for the swivel. It is screwed straight down into the manifold.

**Poil336** · 06-27-2009

yeah, i tried to replace one in the truck i had before this and i found it down underneath it pretty easily, i just couldn't get it out. and i figured the one before the cat would be in the manifold, i'll take a closer look tomorrow or something. could you get to that one from underneath maybe? i'm sure it's after the manifolds come together

**Jakegday** · 06-29-2009

the 2 different sensors throw different codes. what was the exact code? not only will it tell us which sensor it is, it will tell us what the problem is. your sensor may be perfectly fine and is just doing its job by "sensing" a problem, like maybe a wire got cut or something so it cant communicate. or maybe its just trying to tell you your CAT is bad.

lots of possibilities with an "oxygen sensor code"

the exact code would help ALOT

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