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Originally Posted by smartguys
Follow up question:
Do I need 2 or 4 replacement sensors. Many auto parts stores online say 4 per car?
thanks/Kelly
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The pre-cat sensors see a much more harsh environment from a contamination standpoint than the downstream sensors. They are also the only ones that will actually effect the air/fuel mixture. The downstream sensors just tell the DME if the cats are working correctly. You might try replacing just the upstream pair first and see if that fixes your problem.