Question about 2005 Buick LaCrosse
Code 420 means the O2 sensors are telling the computer the catalytic converter on bank one is not working correctly. Bank one is on the side with cylinder one.
The problem could be the cat, or one of the sensors, or a fuel mixture problem such as a vac leak in the engine or injector problem.
The sensors would need to be tested.
Posted on Jan 21, 2013
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Posted on Jan 02, 2017
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