I have a 1995 SC400 with almost 140K miles. Recently the "check engine" and "trac off" lights have been coming on, (the "trac off" light follows the "check engine" light) I have done several searches and found a lot of related info but still have a question or two.

After clearing all codes from the EFI, the system consistently reports error #27 - sub O2 sensor. According to other accounts, this can be symptoms of a failed catalytic converter. Is this true and if so, how can I determine whether it is a sensor or a cat converter? If it's a sensor, will the generic AutoZone Bosch replacements work as replacements in the sub O2 postions?

I appreciate any info you guys can offer, thanks
Mike in Dallas

 

yes. you can replace them with parts you get from Autozone. Make sure the part is cross listed to work with your car.

It's hard to tell which one is bad. a factory replacement cat will be something like $600 per item (MSRP $800) for each.

I would change the 2 sub o2 sensors first. If the cats are bad those will get fouled quickly and throw the check engine light on again in a few days to few weeks. If it does get fouled you have 2 options

to replace the cats with factory cats (don't do this)

or to replace the factory cats with aftermarket.
I got the Carsound 53006 cats for about $70 each.
They will most likely have to go under the car (not at stock location because of size)
Now you take the sub-o2 sensors that have gone bad and you can have the exchanged under warranty. of be honest and buy new o2 sensors.

up to you dude.

good luck.

 

thanks for the quick response - I have read that the sub O2 sensors are accessed tru the floorboard or under the back seat. These screw-in to the exhaust directly? Are they easy to access and remove with no issues?

 

screw in. screw out
They are easy to access.
They can be removed with no issues
They are accessed from underneath the car right behind the cat.

where have you read that the sub 02 sensors are accessed thru the floorboard or under the back seat? any links?

 

I believe I read it here in one of these oxy sensor threads - they may have been referring to the electrical interface. Will see if I can reproduce it

Thanks

 

found it - read down the responses on this one:
https://www.clublexus.com/forums/sho...ck+seat+sensor

 

hmmmm i don't remember having to pull the back seat out.......

if you jack the car up, you will see the o2 sensor plugged in right after the cat.

 

After re-reading the whole thread, I think they were referring or comparing sub-O2 access on an LS400

Will get the sensors and get them swapped. Hopefully, is not the cats. Are you familar with a product that by-passes and eliminates the sub-O2 system?

 

o2 simulator. but if you get those you will not know if the cats are bad or not since it won't throw a code.

 

OK, finally had a chance to troubleshoot this thing. Went by the book and first looked for failed heater circuit on the sub O2's and bingo! the drivers side had zero resistance and was open.

BTW, accessing this was actually pretty easy and really gives one a chance to appreciate the great engineering and modular design of the console assembly. Its no wonder these cars were over $50K new.

AutoZone does not list a generic sub O2 and the OEM units they sell are so high, they are special order only. Has anyone found a substitute Bosch or other generic brand that works on the 95 SC400?

Really would like to pick one up this weekend and get her back on the road

 

try oxygensensors.com

 

Cool - looks like the Walker product is what I am after for <$50

Would you know of any retailer that carrys these?

 

I hope all worked out with your repair.

How can I get codes from my 300sc. The fan speed jumps around on the climate control.

 

96 or later, just take it to AutoZone and they will analyze for you. 95 and previous, I used the under hood DLC, small recatngular receptacle with a pop off cover. The pins are labeled on the underside of the cap. I jumpered TE1 and E1. When you turn the key on it will flash the code to you; ie two flashes, pause, then seven flashes = code 27 which correlated to the subO2 sensor on my car.

good luck

 

how this work out for you?