I have recently bought a 1995 sc300, it’s giving me code 27 (sub oxygen sensor signal)… I’ve been underneath the car and checked everywhere but I’m only finding two o2 sensors. One on each half of the headers, basically I’m just wanting to know how many o2 sensors there should be on my car or which one of those two is the sub o2 sensor. Thanks in advance

 

Hello,

Can you take a picture of what you see under the car?

The sensor should be right under the car, behind the Transmission Mount, facing away from the Transmission towards the Passenger Door, at least that's the case for the 1995 GS300, below is a snippet from the Service Manual. I do not own neither the Manual for the SC, nor the SC itself unfortunately, so a picture of what you see in that area would be helpful.



Hope this helps and best of luck!

 

Some SC300's have just the 2 o2 sensors, some have a third underneath mainly 96+obd2 and 92-95 california models. On the passenger side toward the front, right where the exhaust bends to go under the car from the engine bay there should be an o2 sensor there or a flange for one. It is not after the cat looking thing on the end of the midpipe as that is not the main cat on a sc300. The main cats are right off the header.

 

Unless the previous owner installed a replacement ECU with CA Emissions into a Federal Emissions chassis (these cars are so old now that this could potentially happen)... then you have a CA Emissions SC300 which will have three O2 sensors: two 4-wire heated O2's (on CA 1995 SC300's) on the engine's header before catalytic convertor #1... and one 4-wire heated O2 sensor (the "sub-oxygen sensor") located at an angle right on the #2 catalytic convertor under the car's middle section. It is not easy to see unless the car is jacked up or on a lift.

Look under the hood's lip at the emissions label to be certain of what chassis emission type your car came with.... or you can give your VIN to a Lexus dealer parts department and they can tell you if your chassis is Federal or California Emissions.

On the rare (possible but rare) chance that someone installed a CA Emission 1995 SC300 ECU in a Federal 1995 SC300 chassis then the fix would be to locate a good 1995 Federal SC300 ECU (in the correct trans type) since your car would not have any 3rd O2 sensor wiring and the mis-matched ECU would be issuing a Code 27 for hardware that is not present on a Federal '95 chassis.

From 1996 onward with OBD2 *all* SC300's got the 3rd O2 sensor in that location. CA market versions just got it much earlier.