This is a long shot but does anyone know the part number for the rear O2 sensor on an Evo 5/6? This part is missing from the sites I normally use for parts diagrams (Amayama, Nengun) and I haven't turned up anything useful in research.

Am I safe getting a rear O2 sensor for an Evo 8 (MR578532)? I would assume they are pretty close in terms of cable length and probably the exact same actual sender, though the Evo 8's bolts into the exhaust pipe and the Evo 6's bolts into the catalytic converter itself.

 

For an Evo 5 or 6 (CN9A or CP9A), the downstream oxygen sensor is located in the catalytic converter on the exhaust system. Unlike later Evolution models, the Evo 5 and 6 only have two oxygen sensors total: one upstream (before the turbo elbow) and one downstream.
The part number for the downstream oxygen sensor is a bit difficult to verify definitively due to multiple possible revisions and varying OEM/aftermarket suppliers. Many vendors stock both OEM and aftermarket options.
Location
The downstream or "post-cat" sensor is found in the exhaust system after the catalytic converter.

• It is located further down the exhaust path than the upstream sensor, which is in the turbo elbow.
• The downstream sensor's role is to monitor the catalytic converter's efficiency, not the air-fuel ratio.

Part number

• Genuine Mitsubishi: The original part number can vary by market and specific build, so it's best to confirm with a Mitsubishi dealer using your VIN. Some suppliers list the OE part number as MD348475.
• Aftermarket: You can also purchase a high-quality aftermarket sensor from a reputable brand like Denso

Im sure if you called STM Tuned they could help you find it.

 

Just for posterity that part number (MD348475) has popped up a couple times in my searches and it's almost certainly wrong, I'm almost sure it is for a front O2 sensor and not the rear one.
True, but I probably still need the correct PN to find the right part from Denso.
Also true but I bother their customer service enough as it is and they are not my personal research division, though if I get desperate I'll probably try them out.

 

Send me a vin and I'll see what I can find. Rear o2 sensor looks odd from the parts diagram.

 

Sent it to you but I don't know how much it will help as JDM Evos don't have the 17 digit standard VINs that USDM Evos have.