post cat oxygen sensor

420 is a bad catalytic converter, either there is an air leak prior to converter, O2 sensor bad or converter. most of time it's a converter especially if higher mileage.

what should be the reading than

thank you

Here is an article on to replace the cat

https://www.2carpros.com/articles/catalytic-converter-replacement

so is the cat bad?

If there are no upstream vacuum leaks, most likely the cat is bad, sorry to but in Harry :-)

do you mean by upstream the exhaust side or intake side

Exhaust side, if it was intake side you would have a lean code, not a cat inefficacy code. Here is more information on that

https://www.2carpros.com/topics/trouble-codes/p-codes-powertrain/p0400-p0499/p0420

Thamk you for your help.

is there any chance in the future somebody else answer my questions beside HMAC300. because his answers they are 95% is: take your car to a mechanic:

thank you

when i idle 80% the after cat o2 sensor is lean around 0.1v . when i accelerate (shifting gears) the after cat o2 sensor is a almost a mirror of the pre cat o2.
when i cruise the after cat of sensor is rich around 0.8v. check engine was on , now is off and all monitor are ready including catalytic converter

scan for codes and check fuel pressure with a gauge auto parts rent it.

I checked the fuel pressure is good.
Today the the code p0420 came back.the freeze frame data IS
lTFT 5.5
STFT -2.3
Speed 40
Rpm 2380

That info is good, its telling you you have a cat converter that is weak, this is a common problem

here is more information on how to replace it

https://www.2carpros.com/articles/catalytic-converter-replacement

hoy to reaplace front the oxygen sensor of 2000 mazda protage 4cylinder 1.8L with picture.

There aren't any instructions to post. You unscrew the old one and screw the new one in.

Diagnostic tool brings up code P1170. I have put in two new 02 sensors, the top one and the bottom one, then erased the code from the car, drive about 60 miles and the engine light comes back on giving me the same code, P1170. Any ideas? Thanks in advance

Possible causes
- Faulty HO2S-11 Sensor
- HO2S-11 Sensor harness is open or shorted
- HO2S-11 Sensor circuit poor electrical connection

Scanners are a smart diagnostic tool but can be very dumb at the same time, yes it is saying that there is a problem at the O2 sensor, but you have to look a little deeper into the problem this code is for an open circuit or poor connection and not necessarily a faulty sensor, so you need to check all connections for loose or corroded connections and do a pin out from the sensor back to the ECU to look for open circuit or high resistance, start here.

thank you, I'll try that

OK, good luck with this , these can be tricky to work out, re post if you have any furtjer questions.

Engine Performance problem
2001 Mazda Protege 4 cyl Front Wheel Drive Automatic 12500 miles

I just wanted to ask that if bad gas or air pushing into your tank can it cause or o2oxygen sensor connected towards the muffler to malfuction.

Cause when i went to put gas in and didnt feel prssure of the gas going into my tank..but theyt charged me for the gas and since then check engine like came on and need to repair the above and just want to see if there was dirt or air from the gas pump pushed into my tank could this cause my problem stated above.

thanks

[quote:f50ee6181b="ladybud"]Engine Performance problem
2001 Mazda Protege 4 cyl Front Wheel Drive Automatic 12500 miles

I just wanted to ask that if bad gas or air pushing into your tank can it cause or o2oxygen sensor connected towards the muffler to malfuction.

Cause when i went to put gas in and didnt feel prssure of the gas going into my tank..but theyt charged me for the gas and since then check engine like came on and need to repair the above and just want to see if there was dirt or air from the gas pump pushed into my tank could this cause my problem stated above.

thanks[/quote:f50ee6181b]