P0420
#1
Pit Crew
Thread Starter
P0420
Quick question
Got a P0420 error Bank 1
Replaced Cat on Bank 1
Code came back
However:
- Old gasket from the cat was worn and I didn't have new one.
- Didn't replace O2 sensor (downstream)
Question:
Could it be the gasket or o2 sensor?
or did I get a bad Cat?
Got a P0420 error Bank 1
Replaced Cat on Bank 1
Code came back
However:
- Old gasket from the cat was worn and I didn't have new one.
- Didn't replace O2 sensor (downstream)
Question:
Could it be the gasket or o2 sensor?
or did I get a bad Cat?
#2
More than likely it's a leak on the rear flange where the cat meets the y pipe. If you put your car up on jacks and start the car from a cold condition you will feel and hear a breeze on the upper side of the flange. Doesn't do any good to replace the gasket, the part of the y pipe is worn away from long periods of gas escaping there. The hole just gets bigger and bigger. I patched mine with versachem muffler weld. It is basically a liquid steel product that hardens up after you apply it. I'm guessing your original cat was just fine.
#3
Moderator
I'd check the output voltage of the O2 sensor. If it stays less than 0.3V before and after the warming up, I will check the air leak. The gasket or some other leaking point may be causing the problem.
#6
Moderator
iTrader: (7)
cats rarely go bad so I would have replaced the downstream sensor first before tackling a cat replacement.
http://www.easterncatalytic.com/educ...he-po42o-code/
http://www.easterncatalytic.com/educ...he-po42o-code/
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#10
Super Moderator
iTrader: (6)
Some additional thoughts are that if the O2 sensors are detecting the output erroneously due to age then the air fuel ratio will not be correct. We'd look for other symptoms of these like poor gas mileage and reduced performance. On a car of these ages, O2 sensors are wear items so at 100-125K, they would be best changed out along with the coolant temp sensor, PCV for good measure. These are all low cost items to help insure that the ECU is properly regulating function. The reason being that something upstream is the cause of these "cat" failures. A rich ratio is a factor in seeing a non-functioning cat. For CA peeps when the inspector sees a spacer this would be a visual fail.
#11
Lexus Champion
iTrader: (1)
Some additional thoughts are that if the O2 sensors are detecting the output erroneously due to age then the air fuel ratio will not be correct. We'd look for other symptoms of these like poor gas mileage and reduced performance. On a car of these ages, O2 sensors are wear items so at 100-125K, they would be best changed out along with the coolant temp sensor, PCV for good measure. These are all low cost items to help insure that the ECU is properly regulating function. The reason being that something upstream is the cause of these "cat" failures. A rich ratio is a factor in seeing a non-functioning cat. For CA peeps when the inspector sees a spacer this would be a visual fail.
#13
I have this same problem on my 95.Which sensors do you think are bad?I hate to have to go inside my carpets to replace the rear sensors
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bornking (06-18-18)
#15
Pit Crew
Thread Starter