After my new exhaust arrived today, I crawl under the car only to discover that my 95 (OBD1) BB4 Prelude has TWO O2 sensors - one in the usual place before the cat, and a SECOND one at the tail end of the cat. WTF?? I thought only OBD2 cars ran 2 sensors??

Can the car run without the second sensor? It seems to be plugged in somewhere, but I cannot find a 'secondary O2 sensor input' pinout on any OBD1 P13 diagram I've ever seen. I will have to weld an O2 bung into my cat bypass if it needs it!

 

i've heard that some uk obd1 preludes have 2 o2 sensors, it must be the differernce between our emissions regulations and yours.

are you looking at a p13 pin out diagram for usdm preludes, or one for your european market?

worst case you can try and trace the sensor wires with a multi meter back to the ecu connectors.

 

It's a JDM car - and I have the JDM P13 pinouts. And to my knowledge, NO OBD1 ECU has inputs for a secondary O2.

 

Bump - anyone?

 

Dunno - I'd unplug the 2nd sensor from under the car & drive it around for a few days . . . see if it throws a CEL.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Daemione &raquo;</TD></TR><TR><TD CLASS="quote">Dunno - I'd unplug the 2nd sensor from under the car & drive it around for a few days . . . see if it throws a CEL.</TD></TR></TABLE>

yeah. that'd be the surest way to tell if it's necessary.

 

It's probably an egt probe to monitor your cat's temp. Does it look EXactly like the primary o2 sensor? I know my jdm front clip had an indicator for the cat convertor in the dash( where all the other lights are, cel, brake, oil, ect.)

 

Bump - anyone with any further insights? The 'secondary' sensor appears to have 1 thick wire going to it.....

 

The sensor is supposed to be there.
Secondary O2 sensor with throw a CEL 67
Just leave it connected.

 

Ok, but here's what i don't understand: the ECU has NO input for secondary O2 sensor data - so how could it throw a code?

 

Its the temperature probe.............I also have a JDM (RHD) prelude and the light in the dash came on when I put on a test pipe...................I then moved the probe towards the flex pipe (nearer to engine) and light went out, theoryis that its a bit hotter there.........................
I can imagine a 4th gen '96 with twin O2 sensors, but a 95 theoretically will have just 1!!

 

It has to be the temp probe indeed -&gt; you should have the light under the water / fuel gauges too.

Some JDM ludes have this.

Voila:




Modified by wstef at 10:12 PM 2/19/2006

 

damn....
no sh*t...wowzer...
well you learn something new everyday!

 

So you do! Indeed I found the 'hot cat' light in my dash. Thanks for the info, chaps!

Now then, any ideas on how to bypass this? My test pipe resonator has no bung, and I don't want to go to the trouble of welding one in for something I don't need!

 

I think it is simpler to weld the mounting cut from catalyser than to try to disable this. In plus this is unique It can indicate there is something wrong with engine (ex. running too lean = exhaust gases too hot = not good for engine at all).

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Nalude92 &raquo;</TD></TR><TR><TD CLASS="quote">damn....
no sh*t...wowzer...
well you learn something new everyday!</TD></TR></TABLE>

heh, another exemple: I just realized that USDM ludes have the AUTO switch for driver's mirror going automatically only down. European ludes have AUTO position not only down but also up

 

I would just weld in another place for the second 02 sensor, also. It's really not that hard.

Plus it's unique, like wstef said.