Car People: Some Catalytic Converter Questions

My 2003 Toyota Camry’s check engine light came on today, and I had the error code read by my local auto parts place. The error is that the catalytic converter(s) are not performing efficiently.

Can bad O2 sensor(s) cause a catalytic converter error? Is the car’s computer usually detailed enough to tell the difference?

One many newer cars there’s two O2 sensors (or more). One (or more) is before the catalytic converter many times on the exhaust manifold. This one is mostly used to control the fuel/air mixture. The O2 sensor after the cat is used to tell if the cat is working correctly.

The first rule of using an OBDII code reader: The codes are good place to start the troubleshooting, but you should never, ever change a big ticket item based just on a code. There’s one vehicle I’m familiar with that often throws a knock sensor code. Changing the knock sensor is about a $700 job. And it seldom fixes the problem as the knock sensor code means the engine is knocking or pinging.

Before changing the cat or any O2 sensors, I’d check the wiring to the sensors. They are in a high vibration and heat area and often break at the connectors. Splicing back together a broke wire is a cheap fix.

Next with the engine warmed up from a lot of driving, I’d use an infrared thermometer over the cat to see if you can find any relatively cold spots. That’s a good sign that the cat might be bad.

Next you want to resistance check the O2 sensor. If it passes the sensor is probably good. Some 02 sensors have a heating circuit to get them working faster when the engine is cold. That circuit could be bad and not have anything to do with O2 sensor itself.

How many miles are there on the car? It’s possible that the cat(s) are seeing better days. But before I’d write them off, I’d use some very good fuel injection cleaner like Techron for a tank or two. I’d also go out and do an “Italian Tuneup” by warming up the car and flooring it from a slow speed up to the speed limit a few times. Something like the on ramp of an Interstate up to the speed limit.

I’ve driven our 2002 Camry for years with the same error code. I replaced both O2 sensors and still got the same error code. No way am I replacing the cat.

Thanks for the replies. It sounds as if a good mechanic can and should diagnose the problem separate from the car’s computer, and thankfully, I have a good and honest shop that can take the car.

Could I damage the car if I didn’t replace the converters?
As I don’t live where any sort of Emission or safety inspections are required, I thought about not replacing the CCs at all. Also, the prices for replacement OEM CC parts and O2 sensors are just sky high - it would cost thousands to replace these.

I am seeing references to “Universal” catalytic converters with much more reasonable prices - anyone familiar with these?

I’ve heard rumors that there might be a TSB to the effect that the measured difference between the upstream and downstream O2 sensors is calibrated wrong, but I’ve never bothered to look it up.

I too live where there are no inspections. So long as the converter doesn’t clog up, it won’t damage the car. If it did clog, I’d see if I could just punch out the cat innards with a metal rod and hook it back up.

Universal, after market cats have a bad rep, but I’ve never tried one.

Yes. Inside the catalytic converter is this honeycomb of material that contains the actual catalyst (usually some sort of ceramic coated with a metal like platinum). Over time this catalyst material degrades. At first the efficiency of the catalytic converter just goes down, but eventually the honeycomb material can pretty much just fall apart.

When this happened to my pickup truck, the excessive exhaust pressure (caused by the catalytic converter’s exit being blocked by the loose pieces of honeycomb) forced exhaust gases out through paths that it didn’t normally take, which damaged some seals and completely nuked the EGR valve.

As Kansas Beekeeper said you technically can just punch out the honeycomb material and prevent it from clogging up the catalytic converter and causing damage.

I replaced the catalytic converter in my truck with a cheap aftermarket one. It was about half the price, which I liked. It was also noticeably louder with respect to exhaust noise, but on an old pickup truck I didn’t really care. But then it rusted and split in half when it still should have had many years of life left in it. I got a better aftermarket cat to replace that one, one that actually came with a decent warranty, and it’s still on the truck. YMMV (or YCCMV).

Which one did you get?

It makes sense to verify that the O2 sensor (downstream) is giving plausible readings, but if there’s a catalyst efficiency code it’s a virtual certainty that the converter is faulty. There are different codes that are typically caused by a faulty O2 sensor. And yes, the computer can tell.

Universal converters can be a real pain, as they aren’t shaped or configured to fit any particular car. They have to spliced into the system, sometimes attached by welding, sometimes requiring pipe bending. They typically seem to be of budget quality.

The next step up is an aftermarket “direct fit” converter, designed to fit the specific vehicle it’s listed for. Definitely less problem with installation, and usually of a higher quality level.

Unfortunately, field experience has shown that even the high-quality aftermarket converters don’t work reliably on all makes of cars, and Toyota is one where it needs to be a genuine Toyota part. The aftermarket ones will do okay for two to twelve months, then start setting catalyst efficiency codes. There may be some EPA criteria that they meet, but they just aren’t precise enough in their manufacture and operation to measure up to Toyota specs.

Toyota had some problems with their converters around that era. As a result they extended the emissions warranty on their cars to 8yrs/80k miles but apparently on the cars that were actually found to have the faulty batch of converters they’ve extended it even further. You might want to try calling the dealer and having them run your VIN to see if it just so happens to be one of those.