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I have a 2000 impala 3.8, 202000 miles. This car has a gm

Hello- I have a 2000...
Hello- I have a 2000 impala 3.8 , 202000 miles. This car has a gm second design rebuilt transmission that was installed with 112000 miles on the car. I know that the car needs a catalytic converter. The computer shows codes P0171, P0420 and P1811. Recently it started shifting hard when it gets hot outside or when the engine temperature is above 202 F from 1-2 and 2-3 thus the P1811 code. I have read that this could be a number of different problems with the transmission including the pressure control solenoid. My question is this. Could the fact that I have code P0420 and P171 be the cause of code P1811 setting? The engine seems to run just fine so far but I suspect the need to replace the catalytic converter is causing the lean running condition.
FYI I recently dropped the transmission pan and changed the filter but haven't flushed it completely yet. Transmission hasn't been serviced other than to change the filter and replace lost fluid at 900000 miles to see if it would help the hard shift problem. It seemed to for about a week but the problem is back. GM used Dexron VI with the rebuilt as did I. I don't know what the life expectancy is for a second design rebuilt 4765E is but I sure hope its more than 900000 miles. Any help would be appreciated. Thanks!
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9/20/2017
Gary
Gary, Chevy Technician
Category: Chevy
Satisfied Customers: 17,277
Experience: 15 years GM master tech
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the 420 code and the 171 code will NOT cause the transmission to shift like that

the 1811 code is the pressure control solenoid causing that issue

sometimes having a transmission flush performed with a flash machine can clean the pressure control solenoid out to stop that code

if it returns the transmissions side cover needs to come off and it replaced

as for the 420 code yes the cat is bad

as for the 171 code if there is no vacuum leaks at all replace the O2 sensors when you change the cat and it will fix both codes

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Gary
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Customer reply replied 2 months ago
That's what I suspected. I have experienced transmission shifting problems with a bad cat before on a different car but only at higher speeds... ie. torque converter not locking up just not shifting problems at low speed. Thank you for clarifying. My thought was to pull both transmission cooler lines from the radiator and flush it that way. Are you saying that will not help and only gm or another shop with a flash machine will possibly help? I'm a little leary to try expensive procedures on a car with this many miles unless I know it will help. Also, is it normal to expect a rebuilt transmission to act up in this way with 90,0000 miles?
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