1996 Jaguar XJ6 emissions

1996 JAGUAR XJ6
108,913 MILES • 6 CYL • 2WD • AUTOMATIC
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DENNIS MAHLING
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  • 1 POST
I get a check engine light code PO420 which reads Catalyst System efficiency below threshold (Bank 1) A couple of times the engine ran rough when warm. Could this be a bad oxygen sensor or a bad catalytic converter?

My car also shows a symbol on the dash instruments when I step on the brake pedal. Does this mean the booster is low or bake pads are worn down?
Aug 4, 2008 at 6:32 PM
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JAMES W.
  • ✓ASE Certified Mechanic
  • 2,394 POSTS
  • ASE Certified Mechanic
0420 may be an upstream O2 sensor out of range and leaning your fuel mixture out too much causing a rough idle.
Brake symbol is usually a warning of worn brake pads.
Oct 7, 2008 at 9:20 AM
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