Okay I have seen a couple of threads dealing with this, but I am puzzled to no end.... I have a 92 SC300 and I am getting Code 27 (sub-O2) however there is NO/NO sub-O2. I only have the two one wire O2 sensors that are located on the exhaust manifold. I have the dealer's manual and states that Code 27 is for the Sub-O2 (USA Spec) car. The sticker inside my door says Made in Japan. I also have another car that is the same way (no code however). I have replaced the O2 Sensors TWICE and I have pulled the EFI fuse and still have the code. Can anyone/anyone please help me out with this????? It would be nice to get this figured out.

Thanks!

 

I think I have narrowed down the problem....

I changed ecu's and didn't get the light. I too only have 2 O2 sensors and don't have the 'secondary sensor' like some cars. I do have a plug inside the car for one but there was never one hooked up from the factory. I too got code 27 (secondary O2) and changing the O2 sensors didn't help. I changed ECU's and it seems to be okay now. I want to give thanks to slappy96 for hooking me up with a computer.

Thanks,

 

A friend of mine has the same issue.

Code 27 = Sub-oxygen sensor signal or heater circuit fault

Heater circuit...I'm thinking maybe the ecu coolant sensor is going bad or on the fritz.

Anyone else have any input?

 

did your friend ever figure out the problem? was it the heater sensor?

I am having the problem with another car... when I take the ECU apart, you can see where it is burned on the lower circuit board right up next to where the connectors plug in. Really strange and I have seen this with several ECU's

Please chime in if anyone is familiar with this problem.

Thanks!