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Q:

i replaced all 3 o2 sensors and the engine light is still on and failed emission on 1996 Chevrolet Tahoe

Rookie cbe0621eac06868b3efe0d8d1d3611e23c60d3114864ea2ec19a68cfbd3eebab
code p0140 still come up...why and how can i fix the problem????? please help
(1) Answer
Needs to be scanned with a proper scanner that has live data to monitor rear 02 sensor for correct readings.
Could be lots of causes, poor connections, fuel press. vacuum leak, exhsust leak, defective after market sensor, which is not unusual.