Oxygen sensor number one. Where is it?

[beautysmistress]

I’ve had a check engine light on my 2003 Baja for a while now. The little gadget I bought to give me the code says it’s a bad oxygen sensor number one. Can someone tell me where that oxygen sensor is? Are there only two on the Baja? It looks like this is possibly something I can replace myself instead of taking it to a shop. I just wanna make sure I’m pulling off the right thing Thank you in advance.

[anarchy1024]

There are two: one before the catalytic converter (closer to the engine) and one after. It's screwed directly into the first catalytic converter housing, possibly through a hole in a heat shield (if still attached). It's easy to see from underneath. It should be as easy as disconnecting the cable at the connector, unscrewing the old one, screwing in the new one, and reconnecting the cable... should. However, it can be an absolute b***ard to remove.

With the repeated heating and cooling cycles, rust, and possibly previous mechanics over-tightening it, it's almost guaranteed to not come out easily. You also will likely want an oxygen sensor "socket," which isn't really a socket since it's open at the top and one side.

o2_sensor_socket.PNG (188.24 KiB) Viewed 44 times

Since there's a cable sticking out of the sensor, and since it's quite long, normal sockets won't work (not without cutting something, anyway). I'd also soak it in penetrating lubricant (PB B'Laster, etc.) for several hours, possibly even the night before. Don't try an open-end wrench or 12-pointed box wrench: practically guaranteed to just strip it.

But before you go through all that, make sure it actually is the oxygen sensor itself. The scan tool/code would never say "X part is bad." It says something like "P0135 Code: Heated O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)", which could mean the sensor is bad, or there's a broken wire somewhere, the connector is corroded, a fuse is blown, whatever powers it is malfunctioning, etc. At least, check the connectors, wires, and pins to make sure they're in visibly good condition before trying to remove the sensor.

Also, it typically goes without saying, but be gentle with the replacement sensor (don't drop or bang it, etc.); there's some delicate stuff inside.

[20Baja06]

Great post above! Just to mention it is also recommended, as with many repairs, to disconnect the battery negative cable prior to attempting to remove the sensor.

Here’s the diagram that may help indicate where you need to look:

IMG_5196.png (13.46 KiB) Viewed 24 times