Car throwing 3 of the same codes

David Wagner

Asked by Sep 10, 2015 at 12:17 PM about the 2000 Mercury Cougar 2 Dr V6 Hatchback

Question type: Maintenance & Repair

So my car is throwing P0420 code but it doesn't just throw it once it throws it 3 times had cats replaced and O2 sensors as well and it's still throwing the code 3 times. Would this indicate a need for a computer reflash?

5 Answers


I think there are Two O2 Sensors one in bank one and the other in bank two. Did you replace both, I have also read that after market cats don't seem to work well...

David Wagner

All the o2 sensors replaced and complete OEM Y cat installed. there was 2 at bank 1


Wow I'm at a loss...

Bob Beaman

Check the wiring and the connectors that goes to the O2 sensors.

David Wagner

Ok so they are all working via live readings from OBD2 scanning and they are working correctly with the right voltages and the post cats are not switching super fast versus the upstream ones that are switching faster then the DS ones. All are in nominal voltage readings at idle and 2500 RPM. We have been fighting this issue for nearly a year and can't seem to figure it out. EVERY THING IS NEW FROM THE CATS TO THE O2 Sensors. The question i have is the scanner is throwing 3 of the same code. And I have also noticed after about 800 miles of driving now the Cat and EVAP are both still showing INC Another indication of Computer needing reflashed?

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