I've been dealing with CEL ever since my cats were stolen 2 years ago. Toyota at the time had a 6 month national back order the parts and the t4r is my daily, so I had an independent shop weld up aftermarket cats onto the existing exhaust system which never resolved the CEL light. I recently started searching online and see I can buy OE style manifolds for much cheaper than OEM (almost half the price!!). Has anyone tried any aftermarket OE style manifolds with success in resolving CEL light? Rockauto has brands like doorman, AP, walker that are OE design and EPA compliant. TIA.

they cut the actual manifold cats? There are 2 cats per side; one on the manifold on each side and one lower on each side of the y-pipe.

If it is just the y-pipe cats they took those shouldn't trigger a CEL. you most likely have bad secondary o2 sensors or they messed up the wires to the sensors when they cut the cats off. The cats higher up on the manifold are the ones that matter.

THIS^^^
my understanding is that despite the 02 sensors on the lower cats, they are not monitored by the ECU. In theory, you could just cut off the rear cat and add a O2 bung to the pipe and call it good, as you upgrade the rest of the "questionable engineering" of the T4r exhaust system.

Please note: I am NOT ADVOCATING doing this...just adding to the discussion!
Cut Cats at your own risk...
AMLOR

x2. they must have been really motivated to go after the upstream cats. the secondary/downstream cats have no effect on the o2 sensors. If youre cold, theyre cold, take them off and keep them safe in the garage.

Get the code scanned and post the code here, most auto parts stores will scan it for free

The shop I went to said my primary cats went bad bc I drove around with the exhaust cut up, apparently too much vibration caused the inside of the primary cats to collapse or something. I find it hard to believe but the shop was a friend of a friend of mine so I believed them. They welded new cats directly onto the manifolds. I don’t have secondary cats. I’ve been dealing with this issue for a long time and just want to get it back to stock essentially. I lost my faith in this shop, bc I’ve been driving back and forth trying to deal with them forever and now just want to DIY. I’ll have to get CEL codes again but we tried changing o2 sensors 2x already as the shop has their vendor warranty out the first set I got.

Sounds like some BS that primary cats would have blown out. It's not like its that old and it shouldn't "shake loose" unless it was punched out and pieces were left in there. Either way if they cut off the primaries and welded "something" new in there now it's f'd and you need to buy whole new manifolds with the cats and change them out. Looks like about $900 in parts + labor.