CATALYST OVERHEAT

Hi guys,

I have a 1991 850i. Recently, I've been getting the CATALYST OVERHEAT error on the OBC/MID, complete with tone/beep, immediately after starting the car. Happens regardless of cold/hot, and this is not the quick 2 second one that J-Spec owners see that disappears right away.

The Euro/JSpec cars have after-cat temperature sensors, part numbers:
11 78 1 722 763, or 11 78 1 738 347. Don't want to throw parts at this, otherwise I would have replaced the sensors by now in hopes of it fixing it, but I would rather try and troubleshoot/diagnose this to make sure it's the sensors and not something else.

Anyone ever deal with this?

Info: 1991 J-Spec 850i, Automatic
-Just passed emissions testing recently with great results
-Air filters and sparkplugs(F8LCR) are new, will be doing caps+rotors soon, but since the error comes on instantly, I do not believe this to be an ignition/rich issue
-Behaves the exact same way with both sensors plugged in, both unplugged, 1 unplugged, other unplugged.

thanks!
-Andrew