Suburban Engine code 430

My '98 has 193,000 miles and the catalytic converters were replaced last year. Recently it started giving the subject engine code which is for the left bank catayst efficiency being below normal. First code was for the right bank but I cleared it and all subject codes were for the left bank.

Just before the problem started I flushed the cooling system and replaced the radiator. The truck runs fine other wise. Any one have any suggestions?

Welcome to AF.

Please post your Sub model(K1500?) and engine(5.7?) and GVW(more or less than 8600 GVW (found on a door sticker)).

Were the Cat's a direct 3-way replacement?

Do you have high oil or coolant consumption?

Are there any exhaust leaks?

Yes it is a K1500, 5.7 with a GVW at 7300 lbs. Truck does not use a drop of oil. Pretty amazing at almost 200k but it does not. As for coolant, I replaced the radiator due to a leak in it a few days prior to this problem. The cats were a direct replacement but not OEM. It was 3-way replacment. To my knowledge there is no exhaust leaks. I checked where I could safely put my hand. No obvious sounds indicating a leak either.

New info: It is inconsistent. Yesterday the service engine light came on the way to work - a 14 mile trip start to finish. Again on the return trip. Today, I make the round trip with no code.

Thanks for your help. The truck is in great shape and I can buy a lot of gas for 50 grand!

Yes it is a K1500, 5.7 with a GVW at 7300 lbs. Truck does not use a drop of oil. Pretty amazing at almost 200k but it does not. As for coolant, I replaced the radiator due to a leak in it a few days prior to this problem. The cats were a direct replacement but not OEM. It was 3-way replacment. To my knowledge there is no exhaust leaks. I checked where I could safely put my hand. No obvious sounds indicating a leak either.

New info: It is inconsistent. Yesterday the service engine light came on the way to work - a 14 mile trip start to finish. Again on the return trip. Today, I make the round trip with no code.

Thanks for your help. The truck is in great shape and I can buy a lot of gas for 50 grand!


obviously you replaced the O2 sensors when the new cats were installed....as this is common knowledge that they require replacing at 100,ooomi......the most common cause of cat failure on a good engine is O2 sensor's not working properly...

Actually, I did not replace the O2 sensors. Mine failed because the engine started misfiring on a Sunday evening 200 miles from home. I opted to drive it rather than call a tow truck, rent a car and have to pay to have it fixed in an area where every thing is more expensive. Before that, there was never a problem.

I after correcting the misfire problem, the catalyst efficiency code on the right bank kept recurring at regular intervals so replaced the cats. That was about a year ago. I have not see an engine code since. I suppose it is possible that the misfire and the bad sensor happened co-incident to one another. But the gas milage has not changed in 5 years. Go figure.

I all ears, bring it on. I am going to drive this until I see a Chevy Volt on the show room floor!