[mopar56]

Well my sons 99 Dakota just had a mil light come on the scanner says error code po420, I know this code is related to the o2 in fact it came on a few years ago and after replaceing the rear 02 and several hours of chasing wires I found some wires chafed through the wire harness inside the l/f wheel well behind an acess panel, these were repaired and all was good for the next two years, I had a quick look with a flash light in the dark and rain at the repair I made and it looked ok but after reading some info on po420 it says that an exhaust leak could also trigger this code, the truck has a broken exhaust stud on the right manifold but it has been that way for 1.5 years now and causes no more than a slight tick, do you think a stud would cause this code or any other ideas?, thanks, oh yeah 5.2 l 5spd stick

 

[Bob Lincoln]

Well, a broken exhaust stud could eventually allow it to develop a gasket leak. I'd fix the stud anyway and then clear the codes and recheck them.

"P0420 Catalyst System Low Efficiency" - this can be either a failed catcon or, more likely, a failed downstream O2 sensor.

How does it run?

 

[mopar56]

he said performance is good but it did have a bit of a stumble once at a traffic light today, I am in the marine business some outboards use o2 sensors and they can be tested buy heating the sensor with a tourch and pinning the leads with a volt meter and checking with origanal specs, is there such a test for this one?

 

[Bob Lincoln]

I've heard of people testing them with propane, but that's not an accurate test. Best way is to use an oscilloscope and watch the output change back and forth across the center point at something like 8 times a second. Slow or mostly off-center or reading near one end of the scale is grounds for replacement.

 

[mopar56]

well if it turns out that we end up replaceing the cat has anyone used one of the magnaflow ones?, do they add any performance?