Catalyst system bugs

[Ding1959]

Good morning, fellow owners! Our 2004 Highlander Limited FWD with 3.3L engine was purchased used from the original owner in 2015 with about 127,000 miles. The dash warning lights (check engine, VSC, ABS) come on intermittently. I bought a code reader which shows P0430 (Catalyst system efficiency behold threshold bank 2). We bought a code reader so I can erase the code and it may stay off for a day, a week, two weeks or one time, drove from MN to CA 2200 miles over four days and it never came on until one day after arriving at our CA home! We get 24 mpg at 78 mph and 19 mph in town, starts and runs perfectly. Because it is in such wonderful condition, we intend on keeping it. 

It now has 250,059 miles and has been maintained to the highest degree, no winter salt exposure, original running gear, exhaust and suspension. The vehicle was showing all three warning lights shortly after we bought it, took it to a master mechanic, who pulled a P0430 code and did a pressure check (ok) and replaced one sensor and suggested we use a fuel cleaner additive, which we did. One week later, same lights/code popped up and appear intermittently ever since  At 132,248 miles, replaced spark plugs (Iridium) and intake plenum gasket. At 150,554 replaced valve cover gaskets. At 179,513 replaced timing belt, water pump, coolant. At 204,094 replaced spark plugs (Iridium), upper intake gasket set, both throttle body gaskets, cleaned fuel injectors. At 208,300 replaced bank 2 catalyst with a Walker brand, all four cat sensor. At 233308 miles, replaced intake manifold gasket, thermostat, cross pipe water hose, coolant. At 249215 replaced air flow meter. Denso products were used wherever possible. Intake air filters replaced as required. 

I'm a retired outboard motor mechanic and am astute about keeping our vehicles in top condition, but this cat warning system has not only me stumped, but also five certified repair shops as well. My only thought is that we have a bad electrical ground somewhere. The car will not pass CA smog tests, so cannot get it licensed in CA. MN does not have smog tests, so it remains registered there (our legal residence). Can anyone help us? Thanks

[Toyota Owners Club]

Have you tested for exhaust leak (air being drawn in before or immediately after the cats?

Smallest amount of unregulated air can cause this symptom
Measure the oxygen content at the exhaust = should be zero (0) in O2 content
Also briefly block the exhaust with a rag and listen for any hissing from the exhaust components

[Ding1959]

Thank you, I will look at that shortly. I've had it to many certified master mechanic shops who have all the expensive testing equipment, but the darned lights are elusive. When electronics are intermittent, it's a bear to diagnose them. 

 

[Toyota Owners Club]

Its the only sure fired way to determine if the issue is with something as simple as an exhaust leak.....sometimes the techys don't look at the fundamental stuff first.

[Ding1959]

Thanks for the suggestion, but what's so maddening is the issue is intermittent and exhaust leaks, once they start, don't get better. I will ask my mechanic to check it out nevertheless.