Supra Forums banner

1 - 6 of 6 Posts

·
Supra Owner Since 1996
Joined
·
2,723 Posts
Discussion Starter #1
I'm trying to cure a code 25 problem that I am having and am going to start with the most probable cause, the O2. Question is that since I am OBDII, which O2 do I replace. Logic tells me that it would be the first since the post cat o2 only really tells you how effective your cat is working, but then why would you hook the o2 simulator to the first sensor after removing cats? Or maybe the wiring for the second just runs up to the ecu by the first. I know the OBDI supras (93-95) only have the o2 located in the DP post cat so maybe that is the one I should replace???? Since this is just a hunch I don't want to spend $$$ on the wrong o2. Tonight i will be checking resistance and possibly ohming out my 02 to see if the code continues to show it's ugly face.

In short, which is my primary O2 that the ecu bases air/fuel on?
Thanks
 

·
Supra Poobah
Joined
·
1,391 Posts
The ecu uses sensor 1 for a/f, sensor 2 is for cat degradation as you mentioned. The only way to know if the 02 functions properly is with a scope at operating temperature.
Mike

edit: 02 simulators are hooked up to the second 02 sensor not the first! So if you hooked one up to sensor 1 this might be your problem.
 

·
Registered
Joined
·
247 Posts
Hooking the o2 simulator to the number 1 sensor is a big no no. You are simulating the #2. I believe all year models have 2 o2 sensors. It's just that the OBDI cars don't throw a code when missing a cat.

The first o2 is for regulating your a/f ratio. The second is for telling you if the cat is working. The o2 after the cat is not used for any a/f metering.
 

·
Supra Owner Since 1996
Joined
·
2,723 Posts
Discussion Starter #4
Since the price of a new O2 is about half the price of a Bosch WB I figure I might as well go all out. If it doesn't fix my problem at least I will feel like I didn't waste my money. How many of you use your first O2 port instead of welding in a new bung? I've heard WB generally need to be 12-18in. from the outlet, but how much of an effect is it really going to have if I fab up a bracket and mount the WB in the origional hole?
 

·
Supra Owner Since 1996
Joined
·
2,723 Posts
Discussion Starter #6
I've heard the WB sensor can't take the exhaust head put out that close to the outlet, only the factory narrow band can. Looks like a bung hole for me.
 
1 - 6 of 6 Posts
Top