Help diagnose aftermarket cats and not getting readiness, no CEL

The older these trucks get the more history in each one, and mine is no exception. 2002 V8 4WD 320k miles.

Two years ago the cats were stolen and thief cut the driver rear oxygen sensor harness. Replaced the cats with the cheapest ones at Rockauto and some no-name O2 sensors. Installation was faulty, and for two years there were major (loud) exhaust leaks at the flanges and sensor mounts. Car had CEL the whole time and never taken for emissions test.

That's when I got the truck. Fixed the harness, cleared the codes, replaced the rear sensors before figuring out there was a broken harness wire for the sensor output, did the shop-vac leak test (lots of leaks) and tightened all four sensors and put new gaskets in the four flanges, before and after the cats. And now no CEL but it won't go to readiness on either cats or oxygen sensors. Sensor heating test is fine.

Even after driving it 400 miles in city and highway and doing the factory manual procedure to set sensor readiness (25+ mph for 50+ seconds, idle for 40+ seconds, repeat 10+ times). Still shows the two fields not ready: cat and O2 sensors.

Output on the two front sensors swings between .1 and .9v like they're supposed to. On bank 1 the rear sensor is steady at .2 and the bank 2 is steady at .4v. When I blip the throttle both rear sensors show a brief voltage spike, but no change in the reading on the front sensors. I swapped in another set of rear sensors that I had but no difference.

IR gun shows bank 1 cat at 500F at both the front and the back. Bank 2 is 550F at the weld before and 600F after. That tells me the bank 1 cat is bad, right?

I'm thinking that running 30,000 miles with exhaust leaks and CEL (open-loop) ruined at least one of the cats. Also possible that I still have a minor exhaust leak and perhaps a cracked manifold leak that closes when hot.

My next move is to replace just the cat that has the same in and out temp. It seems everything else is working, and I don't think a small exhaust leak would cause all this trouble. What do you guys think?

 

Think I’d cut the cats out and tune the lights out.

 

I get that but I'm asking for diagnostic help. I gotta pass emissions test to get it registered.

 

I’d swap the downstream 02 sensors and see if the voltage stays the same or tracks with the 02 sensor. 200 mV is low. Should be around 400-500 mV as I recall.

Exhaust leaks could definitely be contributing. Doesn’t your state allow 4/5 emission tests to be complete? I know mine does.

Also, a lot of members here stress to use OEM or OE Denso sensors instead of some generic as problems have been seen in the past. I don’t know the history though.

 

Thanks everyone. The scanner I'm using says it's passed 5 of 7 tests. Here in AZ we're allowed one non-pass. In the VW world there's 8 tests and I've passed emissions with 7 of the 8. I will hit the testing station tomorrow and see what happens. But I do want to solve the actual problem in the meantime.

I did swap a second sensor onto the side that was at 200mv and no difference in output.

 

Readiness is a weird thing. I've seen lots of formulas for lots of vehicles I've owned over the year, none seem to work right. I've found the best way to achieve it, people's and even manufacturer's formulas be damned is one of two ways:

• Trigger each test or the suite of tests with your manufacturer's "OEM" tool (Most support it, but some aftermarket tools may support the same)
• Drive a good mix of city and highway in a day. Run errands to a few stores, but do it by taking the interstate into/out of town and do a good mix of surface roads and highway.

My 99.5 MKIV GTI was a pain in the ass to get into readiness and had me sweating bullets every year at emissions time. That's ultimately why I got the VAG-COM, so I could at least watch the readiness state. I know GM's "Tech2" handheld will complete all readiness testing in a matter of 1-2 minutes with the press of a button. I'm not sure if Techstream will do the same for Toyota.

 

What a coincidence, I have the same problem on my 03 GTI. I could sort of force readiness on some fields using VAG-COM, but it has a tuned ECU from a previous owner and not sure what's going on. Totally worth the hassle, it's a great car.

 

I loved my MKIV. VR6, manual, total blast to drive. Total torque monster, pocket rocket.

 

Well I received some excellent karma today. Went to the testing station with enough paperwork to justify a waiver, but had to actually take the test first. Lo and behold it passed. When I got home my scanner said 7 of 7 fields in readiness, and what's weird is the output on that one rear sensor is still at 200mV or even less. The other is around 500mV. Disappointed to not actually learn anything, but I'll take the win.