Hello all,
Over the summer I started to get O2 sensor codes on my '04 Discovery so I went ahead and replaced all the O2 sensors. Since then, codes P1170, P1173, and P0153 have come back and stayed. The truck generally runs and drives well but has a shake at idle that feels like a misfire although no misfire codes are present. My muffler is also rattling quite badly which makes me wonder if this could all be due to bad cats. Would appreciate any input before I bite the bullet on new cats.

 

ACKD2,
Do you have a scan tool to watch live data? Rattling can be a catalytic converter coming apart, and that will generally be accompanied with a P0420. If you are able to watch live data, check to see what the front and rear 02 sensor voltage is doing. Fronts should cycle between 0-1V. They need to be cycling though. Rears should remain close to 0.450v and hold fairly steady. Let us know what you discover.

 

At this age, it's very likely the cats are bad. Does the exhaust smell sour? Bad sensors will destroy the cats, exhaust leaks will destroy the cats, etc.

The rattle may not be related, it might just be the muffler falling off due to welds going bad, which is common.

 

Personally I wouldn’t jump to replacing the cats. Maybe there’s nothing wrong with your O2 sensors, maybe they’ve been telling the truth all along and your problem is something like a vacuum leak (or numerous other possibilities).