Hey, I'm somewhat new to the forums but really appreciate all of the postings on here. So I have a question that I couldn't find an answer to and I was wondering if the reading for the O2S11 V is for the pre cat or post cat sensor. for our trucks with the V6. As I understand it the pre cat is the O2 sensor and the post is just an air content reader. I'm Getting a P0420 and the O2S11 reading is constant in the high 600 gfi range and the O2S12 has a lot of movement the rough a range of numbers. Could this be a bad sensor based upon these gfi readings or do I need a new toyota catalytic converter. Thanks again.
Trying to Diagnose a Bad Catalytic Converter
- Thread starter tryan68
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kball
New member
What are you using a modus? I assume O2S11 would be O2 sensor bank 1 sensor 1 which would be the pre cat sensor. Depending on what year your runner is it has either two O2 sensors or a pre cat air/fuel ratio sensor and a post cat O2 sensor. I'm not experienced with reading live data but the code you listed refers to the post cat sensor or possibly the cat itself I believe. I'd try replacing the sensor first. If you end up replacing the cat you would want to start off with new sensors anyway.
EatonKyleH
New member
I figured I'd share the testing procedures to determine whether you are dealing with a faulty oxygen sensor or catalyst.
1. Monitor the front and rear oxygen sensors while driving the vehicle at approximately 55 MPH. When the rear sensor switches above and below 0.45 volts, the catalytic converter may be faulty. The rear oxygen sensor should read about 0.6 to 0.7 volts when the catalytic converter is efficient.
2. Monitor the fuel trims both at idle and while driving at steady speeds. Fuel trims should be in single digit ranges and the short fuel trim should be increasing and decreasing 2 or 3 percent. When the fuel trims are out of range, there is a fuel mixture problem or a faulty oxygen sensor and this should be corrected before calling the catalytic converter faulty.
Let me know if you have any further questions via reply of PM.
O2 Sensor or Air fuel
I was wondering if the pre cat sensor is supposed to switch between high and low readings because as of right now both sensors are constant right around .6 after the engine has heated up and Im driving on the highway. From my understanding the pre cat sensor is supposed to switch and mine isn't, so I was going to replace it. BTW this is a 99 limited
I was wondering if the pre cat sensor is supposed to switch between high and low readings because as of right now both sensors are constant right around .6 after the engine has heated up and Im driving on the highway. From my understanding the pre cat sensor is supposed to switch and mine isn't, so I was going to replace it. BTW this is a 99 limited
98OzarksRunner
New member
I had one go bad on my 2nd gen. It smelled something like a dump truck. I figured out what it was when the guts broke loose and it rattled like a dump truck. Took a cat I had from a Lincoln Mk VIII motor I pulled for the block and welded it on. No more rattles, no more smell.
Kung
New member
No more...codes?
'Course, that was a 2nd gen. I keep hearing horror stories about 3G cats. Though I don't live in CA.
EatonKyleH
New member
Responded to your pm and hopefully you understood my explanation. I just came out of surgery yesterday afternoon and was a bit out of it when replying. But the basic thing I tried to explain in that if you have a federal emissions vehicle the precat sensor is an oxygen sensor and should switch. I you have a California emissions vehicle it has an air/fuel ratio sensor which is not a switching type sensor. Let me know which you've got and we can go from there.
98OzarksRunner
New member
No more...codes?
'Course, that was a 2nd gen. I keep hearing horror stories about 3G cats. Though I don't live in CA.
The 2nd gens only have one O2 sensor, so it won't (typically) throw a code for a bad cat. It just stinks and rattles.
