AnbeLexus

Soooo.. My current project is my " new to me " 02 sc430. Ive got a check engine light that comes on and give the code P0330( knock sensor 2 circuit bank 2) and sometimes P0420(Catalyst system efficiency below threshold bank 1) . I've checked the plugs and the coils and both appear in like new shape. I've ran fuel cleaner through several tanks of gas and no change. When the code is off you can drive for quite a while before it comes on if you keep your foot out of the gas but when the motor is put under load it seems to trigger it. I've read up on the knock sensor and have a new one to install but I was wondering if the exhaust system could some how be causing this as well.? I'm looking forward to solving this and getting my sc back in good health and any input would be greatly appreciated !

kevin3344

Been there, done that (on my GS). How many miles on your SC? My knock sensors went right around 210,000 miles on my GS. Had them done at the dealer and while pricey haven't had a problem since. Words of wisdom...do BOTH and be sure and use true Lexus OEM knock sensors or the problem will come back! When I got the P0420 on my GS it was a small exhaust least....odd but the GS400 is known to develop a small leak on the y-pipe. Not sure if this will be the same for you on the SC but get it checked out to be sure.

Coleroad

Let me add to that exhaust leak. It only throws the 420 code pretty far apart. If the motor mounts are worn out you move that connection at the manifold a lot more. This is a huge possibility for it. What has the freeze frame data been each time it's set the code? Fuel trim percentages at idle, and around 3 thousand rpm's? This will show if you have a small vacuum leak that might cause the code. Also misfire numbers for each cylinder. You can have a certain number of misfires before it throws a code for it.

Reminder when clearing codes, Save or print off the freeze frame data. This could become important in quick diagnosis of the issue.

DshngDaryl

I would fix the Knock sensor first. If your car can't adapt to the knocks because of a bad sensor, then it will probably run below efficiency and trigger the P0420 code.