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'97 CAMRY 4 CYL: OBDII code P0420

CEL came on the other day and the corresponding code is P0420 (Catalyst efficiency below threshold (bank 1)). Cleared code so CEL is now off. Mileage is 148,000. Upstream sensor was changed 20,000 miles ago (heater went), still have original downstream sensor. Midas indirectly changed the catalytic converter back in September (blown silencer on that section of exhaust pipe).

I've narrowed the list of usual suspects down to a faulty downstream sensor or flaky new converter. Based on cost, should I have the sensor checked/replaced or have tailpipe emissions checked first? Or should I take the car back to Midas and let them figure it out? Finally, is the downstream sensor part of the closed loop emissions setup or is just monitoring the converter its sole purpose? Thanks.

Reply to
oparr
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Yes, the downstream sensor does affect fuel trim. At $57.79+shipping, I'd just swap it out with a Bosch planar -- and nothing less. I wouldn't use OEM Densos here. The Bosch universal type (#15733) requires splicing the old connector on there, but it's easy to do IMO; otherwise get one with a connector for $20 more.

The catalytic converter is basically a ceramic honeycomb coated with platinum. It's usually the victim and not the villain. So before replacing it (it's too late in your case but for others), I'd make sure the engine is properly tuned up, no internal oil/coolant leaks, timing belt and valve clearance should be correct etc. Make sure there are no vacuum leaks. Make sure there are no exhaust leaks upstream of the sensors/converter.

So swap out the downstream with a Bosch planar (not any cheap thimble type). I hpoe that converter is still under warranty?

BOSCH Part # 15733 $57.79+shipping

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NGK Iridium-IX or Laser-Iridium spark plugs

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Bosch planar type sensor:

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CEL came on the other day and the corresponding code is P0420

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johngdole

Reply to
oparr

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