how many 02 sensors are they on a 99 4 runner? I'm only seeing 2 , but parts house are saying they are 3

 

You're rig has 2. Parts stores list 3 depending on the model. 49 state legal federal models use the same sensor in the upstream and downstream location. California models use 2 different sensors for upstream versus downstream.

Is you truck a Cali model or federal?

 

idk how can I find out?

 

run the vin?

 

Look at the emissions vacuum diagram under the hood. Post a picture if you can.

 

does it have one Cat or Two

Go to the Denso website and look up the part numbers of the vehicle you have.

 

They are confusing. What you want to do is look at the Emissions Information Label
Look for Engine Family in top left corner.

Under there it will say something like: SFI, HOS(2), TWC if it is a 49-state/Federal or SFI, A/F, TWC(2), HOS if it is a Cali. Ignore all the rest of the verbiage.

TWC means Three-Way Converter and TWC(2) means you have two. HOS is Heated Oxygen Sensor. Cali's have one and Feds have two.