CEL P0135, fixed, and now P0420

I have a '97 ES300 with 112K miles. I had got a CEL with P0135 code. I replaced the bank 1 sensor 1 O2 sensor with a OEM sensor. Two days later, I get another CEL and now the code is P0420 - catalyst efficiency below threshold.

I had the P0420 code about 6 months ago and I had replaced the cat. Since then P0420 code was gone and everything was fine.

Any ideas why I am getting P0420 now, after P0135 and after I replaced the O2 sensor? What should I be replacing now?

Thanks, Mark

Reply to
Mark
Loading thread data ...

You should not be replacing anything until you check the Bank 1 Sensor 1, Bank 2 Sensor 1,and Bank 1 Sensor 2 output. Check voltage fluctuation and frequency of voltage fluctuation.

When you replaced the cat, did you use an OEM or an aftermarket cat?

Reply to
Ray O

There is a long history to my cat replacement, which was discussed in this thread here:

formatting link
The summary of that issue was, I initially replaced it with a crappy aftermarket cat. It was fine for ~6 weeks until I had got a fuel injection service. A couple of weeks after that I got the P0420. There was discussion on whether it was the cat that was bad, or the fuel injection service damaged it, or both.

Ultimately, I took it to my trusted mechanic, (the guy who put the crappy cat was a local guy, not my trusted mechanic) who replaced it with a superior quality cat. If I recall, it was either an oem for another car model or just superior in quality. Since then, I didn't have any issues with that cat.

***************

Looking through that thread, there is a mix of good and bad information and advice.

Aftermarket cats are a hit-or-miss proposition, and I've read and heard of more people with bad luck than good luck with them. As expensive as OEM cats are, IMO, they are the only way to go.

At this point, check the O2 sensors as I mentioned above. If the Bank 1 Sensor 2 checks out, then the cat isn't working properly.

Reply to
Ray O

Since I just replaced the bank 1 sensor 1 with the OEM sensor, I suppose it would be okay to "mix and match", and replace the downstream sensor with this bosch one? After my cat experience, I'm just too skeptical to use non-oem parts for emission components, so pardon me if my questions sounds silly.

Thank you.

************ It is OK to mix OEM and aftermarket parts, but before you go and replace any sensors, check their function. I suspect that B1S1 (Bank 1 Sensor 1), B2S1, and B1S2 are all OK because the nature of P0420 means that B1S2 sees a signal that matches B1S1 instead of a more steady signal that would result if the cat was working. If the sensors are good and the cat is bad, you would probably end up with the same trouble code.

Checking the sensor output voltages and frequencies would eliminate them as the cause and point to a bad catalytic converter. If you don't want to bother checking the sensors and prefer to just replace parts in hopes of solving the problem, replace the aftermarket cat with an OEM one. Of course, an OEM cat is fairly expensive, so spending 10 or 15 minutes to check the sensors is probably worth the time.

Reply to
Ray O

hey Ray,

this is probably a dumb question, but isn't the emission system, specifically the cat system, supposed to be covered by the manufacturers warranty for something like 100k miles?

Reply to
01dyna

I don't consider any questions dumb the first time they're asked. The catalytic converter and O2 sensors would be covered by the 8 year, 80,000 mile federal design and defect warranty, but the OP's 97 ES with 112,000 miles is outside of warranty coverage by time and mileage.

Reply to
Ray O

I took the car to my mechanic to have him check the other two O2 sensors. He asked me to buy 'catalytic converter cleaner' and put it in the gas tank. That should clean the cat and the CEL should go away. Anybody have any prior experience with this cat cleaner? Does it work? Does it do any harm? I wouldn't mind trying it as long as it does not cause more damage.

Reply to
Mark

I doubt if the catalytic converter cleaner will work, but it probably wouldn't hurt to try it.

Reply to
Ray O

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.