Post cat oxygen sensor

Tiny
ZEMORZEMOR
  • MEMBER
  • 2000 MAZDA PROTEGE
  • 1.6L
  • 4 CYL
  • FWD
  • MANUAL
  • 170,000 MILES
I have intermittent check engine light p0420. I checked the voltage of the post cat oxygen sensor it was fluctuating between 0.420 to 0.435
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Saturday, February 6th, 2016 AT 11:13 AM

20 Replies

Tiny
HMAC300
  • EXPERT
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.
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Saturday, February 6th, 2016 AT 1:16 PM
Tiny
ZEMORZEMOR
  • MEMBER
What should be the reading than

thank you
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Saturday, February 6th, 2016 AT 2:48 PM
Tiny
KEN
  • ADMIN
Here is an article on to replace the cat

http://www.2carpros.com/articles/catalytic-converter-replacement
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Tuesday, February 9th, 2016 AT 6:28 PM
Tiny
ZEMORZEMOR
  • MEMBER
So is the cat bad?
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Wednesday, February 10th, 2016 AT 7:10 AM
Tiny
KEN
  • ADMIN
If there are no upstream vacuum leaks, most likely the cat is bad, sorry to but in Harry :-)
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Wednesday, February 10th, 2016 AT 2:42 PM
Tiny
ZEMORZEMOR
  • MEMBER
Do you mean by upstream the exhaust side or intake side
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Wednesday, February 10th, 2016 AT 6:28 PM
Tiny
KEN
  • ADMIN
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
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Thursday, February 11th, 2016 AT 11:09 AM
Tiny
ZEMORZEMOR
  • MEMBER
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
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Thursday, February 11th, 2016 AT 8:32 PM
Tiny
ZEMORZEMOR
  • MEMBER
  • 2000 MAZDA PROTEGE
  • 1.6L
  • 4 CYL
  • FWD
  • MANUAL
  • 172,000 MILES
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
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Tuesday, December 20th, 2016 AT 2:50 PM (Merged)
Tiny
HMAC300
  • EXPERT
Scan for codes and check fuel pressure with a gauge auto parts rent it.
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Tuesday, December 20th, 2016 AT 2:50 PM (Merged)
Tiny
ZEMORZEMOR
  • MEMBER
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
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Tuesday, December 20th, 2016 AT 2:50 PM (Merged)
Tiny
KEN
  • ADMIN
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

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

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Tuesday, December 20th, 2016 AT 2:50 PM (Merged)
Tiny
VESHKI
  • MEMBER
  • 2000 MAZDA PROTEGE
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 103 MILES
Hoy to reaplace front the oxygen sensor of 2000 mazda protage 4cylinder 1.8L with picture.
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Tuesday, December 20th, 2016 AT 2:50 PM (Merged)
Tiny
WRENCHTECH
  • EXPERT
There aren't any instructions to post. You unscrew the old one and screw the new one in.
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Tuesday, December 20th, 2016 AT 2:50 PM (Merged)
Tiny
SHERISHERI
  • MEMBER
  • 2001 MAZDA PROTEGE
  • 1.6L
  • 4 CYL
  • AUTOMATIC
  • 100,000 MILES
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
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Tuesday, December 20th, 2016 AT 2:50 PM (Merged)
Tiny
MHPAUTOS
  • EXPERT
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.
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Tuesday, December 20th, 2016 AT 2:50 PM (Merged)
Tiny
SHERISHERI
  • MEMBER
Thank you, I'll try that
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Tuesday, December 20th, 2016 AT 2:50 PM (Merged)
Tiny
MHPAUTOS
  • EXPERT
OK, good luck with this, these can be tricky to work out, re post if you have any furtjer questions.
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Tuesday, December 20th, 2016 AT 2:50 PM (Merged)
Tiny
LADYBUD
  • MEMBER
  • 2001 MAZDA PROTEGE
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 12,500 MILES
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
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Tuesday, December 20th, 2016 AT 2:50 PM (Merged)
Tiny
LADYBUD
  • MEMBER
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Tuesday, December 20th, 2016 AT 2:50 PM (Merged)

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