2003 Pontiac Grand Prix scanner codes

Tiny
SIMPLEMANTL
  • MEMBER
  • 2003 PONTIAC GRAND PRIX
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 65,000 MILES
Can you tell me what things to check with a scanner code 420 catalyst effecency below threshold bank 1
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Saturday, January 5th, 2008 AT 11:39 AM

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Tiny
FISHERMAN
  • MEMBER
Hello !

1, The oxygen (O2) sensor. It might be damaged or not working as it should.

2, The temperature sensor for the engine coolant. It might be damaged or not working as it should.

3, Check for problems or damage on your exhaust manifold, catalytic converter or your exhaust pipe.

4, The ignition (spark) timing might be wrong.

Any of the above items should be checked. But your best bet is to check the the oxygen sensors or your catalytic converter first. They might need to be replaced.

Good Luck!
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Saturday, January 5th, 2008 AT 12:08 PM
Tiny
MASTERTECHTIM
  • MEMBER
Definately check your warranty to see if its covered. This code is pretty foolproof, your converter is definately not up to snuff. It basically tells you that the o2 sensor behind the converter is reading the same as the o2 in front of the converter which means the converter is not working. In theory your rear o2 sensor should be steady while the front one toggles high and low frequently.
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Saturday, January 5th, 2008 AT 5:28 PM

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