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Hello,
I am trying to clarify exactly what i have...

I think i have 3 catalytic converters - one on each bank of 3 cylinders and a 3rd on the common pipe before the silencer/muffler
I believe there is an A/F sensor (also known as Sensor 1) above the cat on each bank, and an O2 sensor (sensor 2) below the cat on each bank. There is another O2 sensor after the 3rd cat and before the silencer/muffler.
The two A/F sensors are known as 'upstream' sensors, the two sensor 2 sensors are known as 'downstream'. What is the 3rd O2 sensor further downstream called?

When i get a P0420 error code, does that indicate that all 3 cats need replacing, or just the one on the common pipe?
For a P0037 code (Bank 1, sensor 2) that means the downstream sensor on bank 1/rear bank NOT the 3rd O2 sensor. Is this correct?

Thanks for your help
 

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05 camry 07 tacoma
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P0037 is error code set by the bank1, sensor 2 located after bank1 cat. It is not for the 3rd (S3) sensor.
P0420 is error code for bank1 cat only.. Before replacing cat fix the P0037 may be a connection.
 

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05 camry 07 tacoma
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A more accurate approach would be to measure the sensor heater circuit first.
The sensor heater itself should read around 14 ohms.
If shorted or open then of course would need to be changed.

Let us know how it comes out and if P0420 continues to set after the P0037 fix.
 
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