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P0141 = Downstream HO2S Heater CKT Malfunction.
This is not an O2 problem but the heated circuit and it should not be related to the catalytic converter. Either the HO2S sensor or its wiring circuit is faulty.
P0136 = Downstream HO2S CKT Malfunction.
This is either due to a fault in the HO2S or the catalytic converter.
P0421 = Catalyst efficiency.
This is most probably due to a bad catalytic converter but a faulty O2 sensor can cause it, vice versa it can cause a bad O2 reading and indicator malfunction.
I have attached a diagnostic for the P1506 and it is self explanatory.
Emission trouble shooting sometimes can be sticky as engine performance can cause it to happen as well. When burning rich or lean, maybe due to vacumn leakages, air flow clogging, fuel pressure low etc can cause it to happen so it would be best to do test and checks first before proceeding with replacement of parts.
I believe the catalytic converter is due for replacement.
Monday, December 8th, 2008 AT 3:21 AM