legacycentral bbs

i live in alberta and the emssion control here is still very laxs. so i was wondering if the O2 senor was a before or after the first cat

Which car?

I know the stock Turbo legacy is on the DP before the cat

As for an NA I don't remember

There should always be atleast one o2 before the cat.

As far as I know only OBD2 (96+) cars have a second O2 sensor after the cat. It's specifically to tell the ECU if the cat is doing it's job or if it's gone bad. Doesn't have any effect on the engine like the first one does.

Actually from what I've read, on newer OBDII cars the the post cat O2 sensors main function is to check catalyst efficiency/threshold, but it also has a small effect on Total Fuel Trim.

brweber352 I thought that was only after like 2004 or something

its 94 turbo but from the sounds of it ill be able to make the switch with no problems

Not sure of exact year, I think it's different from manufacturer to manufacturer but I was speaking generally of the newer ob2 cars 2000-up and also CAN. Personally, I treat all O2s (pre-post) equally, and would replace any I suspect are bad.

Since the car is a 1994 Turbo Legacy you only have 1 O2 sensor and it is right after the turbo, before the cat, and is accessable from under the hood.

thanks guys

This recent post may be of interest http://bbs.legacycentral.org/viewtopic.php?t=43096

sorry for the thread jack, but i have a 94 NA and i have 2 o2 sensors, whats the second 1 for?

The second one would be for the ecu can tell if the cat is working. I believe it takes the reading from the first one and then compares it to the second on.

so with no cat, that's probably pretty useless. So is there a way to get rid of it, without setting off the check light?

If it's a 94 Legacy, there should only be 1 O2 sensor. If it's running the stock ECU, there's not 2nd O2 sensor or cat monitoring on the OBD1 computers.