Do I need new cats?

Howdy 2004 TRD V6. Just installed denso dnstream 02 sensor to eliminate p0136 cel. Just came back on. Ordered new denso upstream. If that don' fix it, how can I tell if my cats are bad? And which one? Truck runs/ starts great. No other symptoms. Rarely get small evap leak cel but vsv valves check out And I can' find any cracked hoses. Thanks to all who reply.

 

Did it come back as a P0136? That is o2 voltage low which would indicate a o2 sensor or wiring issue or some sort of magic extremely good cat. Cat usually leads to a P0420 code instead indicating high voltage or poor cat performance. You 100% sure you got the right replacement sensor?

 

I put in a

$170 denso 234-9003 air fuel ratio sensor

denso 234-9003 connects under passenger seat. (Got lucky and didn't brake the studs)

 

There's your problem,

$170 234-9003 Air Fuel Ratio Sensor

234-9003 is the upstream sensor, downstream part number is

$61 234-4189 Oxygen Sensor

234-4189

 

P0136 is not necessarily cat related, but sensor related. Check the FSM for that code attached below.

 

Yeah, upstream also. Changing it may solve the problem.

I had this code a while back. Changed the sensor. Still had the code, and no other codes. Did the diagnostics, and everything checked out. Checked the wiring and connections, including the relay. Maybe reconnecting the plugs and relay fixed a bad connection because that code did not come back, but I got new ones for EVAP leaks. Has a bad VSV, and it's been good ever since.

 

drive her hard for 10 minutes, then get out an look to see if the CAT is glowing red ( from heat ) if so its more then likely faulty.

 

I don't think that necessary in this case. The computer will throw a DTC when the cat efficiency drops below the minimum. Even then, there may be another cause. I had a low efficiency code, and it turned out to be a leaky gasket ahead of the downstream sensor. I'm still running the original cats.

 

Got the sensor and wideband in the right locatioms. Still got cel. Turned out tobe the gasket was not sealing because the stud threads are crappy and the nuts ( ne w ones caust the old ones rusted out) tightened up before the gasket was squeezed enough to seal. Some washers inder the nuts solved it. Mo cel so far. BIG THANKS TO ALL.

 

Man do i got fat fingers.....