Hi, I just got the P0500 code last week and replaced the VSS. Last night the check engine light came on again and I got the following codes: P0138, P0500, and P0130. Two of the codes are for an O2 sensor. Where is/are this/these located, and are they easy to change? Thanks a ton!

 

There are 4. right around your catalytic converters. They are good for about 80K and then they start going out. If you are around that, replace all 4 at the same time. They are for your driver's side. ( Bank 1 ) and each one has a fault front (sensor1) and rear (sensor 2). The other is still for your VSS. might want to check you connections..

 

Ditto!!

 

Thanks a lot, guys! Would you know anywhere I might be able to find photos of where the sensors go.

 

Can't miss them. Follow your exhaust out of the manifold. One in each "footwell" area, the others are downstream before the cat.

 

I've been looking for replacement O2 sensors on-line (I've decided to just change all 4). I see that if you buy them with just the sensor and a short length of wire (without the hookup thingy) they're about 1/3 the price. Is this the way to go, and if so, how can I tell how many wires there are in each? I've seen "two wire", "three wire", and "four wire". It's a '99 Discovery Series I.

 

It's recommended NOT to go with the cheaper ones. You have to splice the old plug and doing so is said to screw with the voltage/resistance (or whatever) across the wires and give false readings, resulting in poor performance/failure.

If I recall, the O2's are 4 wire.