nwagtmustang

I have been burning oil and the check engine light comes on. Code is p0432. Main Catalyst Efficiency Below Threshold. I reset the light and comes back on every 3 days or so and stays on until I reset it. I am getting a new engine installed this week but was curious about the cat?

PeterB

From my experience. Yes of course it can.

My last 2000 JGC Limited was purchased with 600 miles and I drove her over 310k.

The past 3/4years she burned about 2 quarts of oil per month. I replaced my cats prior to having immission testing done here in Illinois with aftermarket cats, check engine light would go off, I pass emissions and about 3-6 months later check engine light would re appear. I would go back to the cat place, replace it out under the 1 year guarantee and on and on.

Whether it was due to cheap ($179) aftermarket cats or not, I can't tell you what I can confirm is that I burned a substantial amount of oil as a result it corroded them up is what I was told. Perhaps others will chime in with their knowledge that it does not but I'm of the opinion it does. My .02

Good luck and stay well.

PeterB.

5-90

Yes.

Even an overdose of blowby can poison the catalyst bed - that's how we got saddled with the "Energy Saving" API SM oils with the lose anti-scuff additive content that is wiping out flat-tappet cams (most OEMs of gasoline engines are using roller cams now - and have been for a few years. Doesn't do us guys with older engines a whole lot of good tho.)

It's the organometallic additives (primarily ZDDP) that get into the catalyst bed and degrade its overall efficiency, which pushes catalysis down and throws a code under OBD-II.

Correct the cause of oil loss (most often valve guide seals,) replace the cat, and make sure you are not using "Energy Saving" oil (API Service Spec SM or SN, no corresponding Diesel - C - spec) or add something like General Motors' "Engine Oil Supplement" to the API SM or SN oil to preserve your camshaft. Roller bumpstick kits for our beloved AMC six are still cost-prohibitive.

nwagtmustang

I am replacing the engine this week so that will fix the oil burning. I am sure its the valve seals but due to low compression numbers I decided to go with a reman engine. Will be done by Friday. I do know they are original cats. Atleast by fixing the oil burning the cats will not get any worse. I jist passed emissions in april so im good for 2 years.

nwagtmustang

I found out some interesting news. The shop got the engine out yesterday. I stopped by today to look at it and they gave me some info. He said the 3rd cat was cut open, innards taken out, and then the piece welded back on. The first 2 cats are good. So Im guessing due to the engine burning oil and the 3rd cat being not existent that is why I was getting the code of cat being under threshold. However I then started doing some research and came across a dodge website. Somewhere in the thread it was stated that the first 2 cats are monitored by the 02 sensors and the 3rd one is after the sensors. I was under my jeep before taking it to the shop but I don't remember looking at the cats and seeing where the o2 sensors were compared to the cats. I know I can call the shop, but I was going to ask them that when I pick it up this week. Ever since I bought the jeep even before it started burning oil I could smell exhaust. I thought it was a leak but now thinking it is because there are 2 cats instead of 3. The plan for now is keep the cats as is since it did pass emissions testing and if it becomes a problem then go with all new cats. I was just curious if someone knows the cat and o2 sensor setup for a 99 grand Cherokee with 4.7l engine?

autosurgeon

There is no way for the rear cat to effect codes as there is no sensor behind it. The only reason it is there is so the vehicle will pass CA smog.

nwagtmustang

That is what I wanted to confirm, if the 3rd cat is after or before the downstream o2 sensors.