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Welcome to the forum. That DTC is not necessarily indicating sensor 1 is bad. It may not even be a bad sensor, a lot of things can cause that - a bad or clogged cat might be the most likely. The troubleshooting steps are in the Factory Service Manual found here. Go to section EC and lookup that DTC.
Last edited by MikeG35Coupe; Dec 14, 2022 at 09:30 AM.
Sensor1 (the upstream ones in the headers) are for measuring air fuel ratio, the downstream ones (in the catalytic converter) are for catalytic efficiency.
Normally those kinds of codes are caused by an exhaust leak at the flange between the catalytic converter and the header, if you don't have an exhaust leak it's probably the downstream O2 sensor.
The computer compares the values of both sensors to determine how much the cats are actually doing, if you introduce outside air into the system because of an exhaust leak it REALLY throws the system off.
However I personally like to just remove the cats and inspect them with a flashlight and borescope camera (VQ engines have a bend in the pipe so you can't see one end of the catalytic element) to make sure there aren't any melted looking spots on the front or rear of the element itself. That would indicate the catalytic converter itself is failing which could also cause that code.
If the gasket LOOKS good and isn't cracked then you can reuse them, just make sure to torque everything to factory spec.
It's easiest to remove the Y-pipe first since there's a lot more play in that section, trying to remove just the cats with the y-pipe still in place is a pain in the ***. EDIT: It's super easy to pull the y-pipe.
MAKE SURE YOU ARE ONLY USING 6 POINT SOCKETS OR WRENCHES ON THOSE EXHAUST NUTS/BOLTS OR THEY WILL STRIP OUT! And use a liberal amount of penetrating oil like PB Blaster PENETRATING oil.
Also, the forward facing bolts on the cats you will need about 36" of extensions and a knuckle to reach down from the top of the engine bay, passenger side is easy, driver side you have just enough room between the steering shaft to reach the bolt (with the intake tube removed).
