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#1
01-26-2007, 02:57 PM
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Catalyst Efficiency Below Threshold PO420??
 1999 Malibu LS. 3.1L This car is driving me nuts! So far I have replaced the catalytic converter and back O2 sensor and the fuel pressure regulator. Just had to have the engine rebuilt because the piston cap broke off and wedge between the crankshaft and engine wall. (ouch) Now after driving maybe 300 miles since the rebuild I get the check engine light with the PO420 code coming up! (Had it checked at AutoZone) Anyone have any idea what else is going on with this thing? -also we aren't sure if this is the original engine on the car; any idea on how we can find out what year it is?- Thanks! 
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#2
01-26-2007, 03:39 PM
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Re: Catalyst Efficiency Below Threshold PO420??
The PCM uses a comparison between the front and rear O2's readings to monitor catalyst efficiency, so try replacing the front o2 before going any further.
__________________
 Still waiting for the "good old days" I'll get to bore my future grandchildren with!
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