Please Help (error code)

[RaveSensation]

OK....so heres the deal. I keep getting an error code on my 98' Chevrolet V8 305 engine. The error code is

P0420 Catalyst Efficeincy Low Bank 1

Now...I dont know what that means. Do I need to change an O2 sensor, and if so which one, or is it something major I just dont know. I recently about 4months ago replaced my transmission. Complete rebuild so it is brand new. I notice a few months later that when the truck shifts from first to second (automatic transmission) it sometimes jerks, as if a shift kit was put on. I took my truck back to AAMCO. The guy that did the transmission I truly trust and value his opinion. He said that the above error code can cause the pressure of the lines to transmission to cause this jerk. What do I need to do to correct this problem?
Thanks
Casey

[2000CAYukon]

This code is set when the 02 sensor after the cat detects that the cat is not working properly. This could be a bad 02 sensor or a bad cat. Many just replace the rear 02 sensor first before replacing the cat.

//2000CAYukon

[Fireplug]

BANK 1 is a pre cat sensor should be on the drivers side exhaust manifold

[RaveSensation]

I replaced the second one on the drivers side...right next to the transmission. the one on the manifold first ...thats the one that needs replacing?

[Jeremy-WI]

Actually two O2 sensors should monitor the catalyst efficiency if it has a single catalytic converter which is standard on the 4.3 and 5.0. You could have tried swapping the two O2 sensors closest to the catalytic, one is between the cat and y pipe(Bank 1, Sensor 2) and the other is between cat and muffler(Bank 1, Sensor 3). Bank 1 just means the drivers side of the exhaust system and with a single cat anything after where the drivers side and passenger side exhaust mix together(Y pipe) is also considered Bank 1

[RaveSensation]

would this cause the transmission to jerk from 1st to second. the guy who rebuilt my transmission said that the jerking from 1st to 2nd is caused by this error code. is that true?

[GMMerlin]

Originally Posted by RaveSensation

OK....so heres the deal. I keep getting an error code on my 98' Chevrolet V8 305 engine. The error code is

P0420 Catalyst Efficeincy Low Bank 1

Now...I dont know what that means. Do I need to change an O2 sensor, and if so which one, or is it something major I just dont know. I recently about 4months ago replaced my transmission. Complete rebuild so it is brand new. I notice a few months later that when the truck shifts from first to second (automatic transmission) it sometimes jerks, as if a shift kit was put on. I took my truck back to AAMCO. The guy that did the transmission I truly trust and value his opinion. He said that the above error code can cause the pressure of the lines to transmission to cause this jerk. What do I need to do to correct this problem?
Thanks
Casey

A P0420 is caused by a catalyst that has loss efficency.
Replacing the converter will fix this problem.
This code should not change the shifting pattern of your transmission unless the converter is physically starting to come apart and clog.
This code does not put the PCM into a default mode.If the converter was clogged, you should notice a loss of power.

[LastOne]

My 98 has this code but real problem is a misfire on a cyl. Some type of mech problem with the head. It runs too good to tear it down so I just have an extra nightlight (SES) to guide me home!

[RaveSensation]

Thanks guys....Ill let you know what happens.