O2 Simulator or Replace Cat?

Hey there, trying to decide whether to fix my truck correctly by replacing the cat or throwing in an O2 simulator. Not 100% sure it’s the cat. Need to do some more diagnostics to make sure it definitely is. The upstream cat rattles when you bang on it. Exhaust shop said there was no exhaust leaks. Truck also run with a lean code for who knows how long before I bought it. Dont really want to drop the money on a OEM cat and not sure how good the aftermarket ones are.

Thanks,

Eli

 

if there is loose material in the cat it is just a matter of time before it plugs either the rear cat, if equipped, or the muffler. I have O2 simulators on all of my Tacoma's that reside in Mexico due to poor gas.

 

If push comes to shove, I replaced my original factory cat with a Magnaflow from L C Engineering. It's legal and well-built.

 

I have been running Walker Exhaust products with no problems .

It is good to know the real problem before replacing things.

It would suck to go either route and still have the code.

 

LCE sells a test pipe depending on your location for 95.00

 

I use aftermarket cat with no problem. If you have a lean code, you might have superheated the front cat causing it to break up. Fix the lean issue firstly.

 

It's best to fix the actual issue before potentially compounding it with another issue. Cats shouldn't rattle so that will need replacing.

 

I have owned by truck for six years and had been driving it without a cat with a rear O2 standoff. I just installed a cat and new exhaust and it’s like driving an entirely different truck. It runs awesome. Don’t leave it out. RockAuto sells decent ones.....

 

I've been running front/rear Magnaflow cats for almost 4 years now with no issues, they aren't that expensive and way cheaper than OEM ones.

 

O2 simulator is very illegal and there’s some hefty fines if you get caught. Depends whether your state requires inspections, etc.. so you can decide whether it’s worth the risk. Plus selling it with an O2 sensor simulator could also get you in trouble. Fix the root of the problem and just put a new cat on. You can scrap the old ones to make some of the money back. The platinum in them is very valuable.

 

The URD simulator goes inside the cab under the passenger seat. It connects to the downstream sensor connector. I seriously doubt you’d ever get caught with it by a regular state inspection. It’s less than $150.00 if I remember correctly. You should be getting a catalyst efficiency code for the simulator to cover up the bad or gutted converters. If you have a lean code, the simulator will not fix that problem, nor will a converter. Like mentioned in earlier posts the lean code could have contributed to the failed converter. Lean or rich codes come from your upstream o2 sensors which are before the converters. Catalyst efficiency codes are set by the downstream o2 sensor. Your ECU constantly adjusts air fuel according to the feedback from the upstream sensor, which will directly affect drivability. Now your next task is to find out if the engine is actually running lean, or do you have a sensor problem. FYI lean codes are very very rarely set by a bad O2 sensor, but it is possible.

 

I had a P0171 code for awhile and fixed that by replacing the MAF sensor. Now it’s just the P0420 code. I’ve just been clearing it for awhile now.

 

That's what I did too for awhile, but replacing the cats was the only thing that fixed it.

I live in CA though and had to so I could pass emissions

 

Yeah, I need to go ahead and fix it some point. What’s the best test to confirm it’s the cat? I’ve seen people reading the live data from the rear O2 sensor. Is there anyway to tell if it’s both cats or just one?

 

Tbh I just took it to Toyota and they were the ones that told me they confirmed it was the cat. Front cat specifically, but recommended I replace both because if you drive for a long time with the front bad then it's likely the rear isn't too far behind. So I just had an exhaust shop replace both with 50 state legal Magnaflows. P0420 disappeared for good after that.

 

Not sure if it was related or not, but not long afterward I got a code for a bad rear o2 sensor (P0136). Took it out and it looked fried. Replaced that too and it took care of that code.

 

How is it that these OEM cats are failing?... doesn’t make sense

Mine is still original at 635,000

 

Previous owner ran it with the P0171 code for awhile it sounds like. I assume the lean condition killed the cat

 

I thought running it rich kills a cat, not lean.


Two conditions can kill a catalytic converter. First, rich fuel mixtures and exhaust leaks can cause excessive heat which can cause the matting to erode and eventually the ceramic substrate to melt. Second, contamination from oil, coolant and other substances like sealants can block the catalyst surfaces.

 

True, but an oxygen sensor is sometimes just stupid, well not exactly it just does what it’s supposed to. It creates voltage related to oxygen inside the exhaust. Scenario time, let’s say your engine is misfiring. A misfire code should also be present but that’s not always the case. When the engine misfires it sends all the oxygen and unburdened fuel into the exhaust, the oxygen sensor is only reacting to the oxygen, not the raw fuel, causing it to read lean. The converter will overheat and fail due to all the raw fuel and oxygen it needs to burn it. The combustion is now taking place in the converter instead of the cylinder that’s misfiring. Given this problem should be noticed by the driver, but as a technician, like I am, you can’t always depend on what the customer says in relation to what is actually wrong. For instance maybe this particular customer came in and only stated that the check engine light was on. If you were to have lean codes and misfire codes, you should always address the misfire codes first. Lean codes can be caused my a number of things. Just an example of an o2 sensor reading a lean condition when in actuality the exhaust is also rich with fuel.