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So had a bad o2 sensor for bank 1 sensor 1, replaced it by myself since i was a newbie i messed up and damaged the sensor it was NTK 24302, i left it there in the hole and later in august i ordered a new one and got it replaced by a nearby mechanic. he seemed very confident and told me that once install we have to keep the wires away from the engine block due to heat, so he pushed them hide them under something, today after like 3 months while driving on the highway the engine light came on again and its the same code again, i wonder if its the sensor again or something again. Could it be a faulty part, should I have ordered Denso one instead of NTK, any other advice? Also back when the first time the sensor was bad, I had code p0134 and after I changed the sensor the code disappeared and now the code is P0420. Any advice would be great?
P0420 means you have (most likely) bad cat, not a bad sensor. Might be also an exhaust leak. Google how to find out if you have bad cat.
Most people use IR thermometer and compare cat's inlet and outlet temps, or use live data and compare the sensor 1 and sensor 2 readings.
There are movies on YT showing the process.
it COULD also be the downstream sensor as well, B1S1 sounds like the upstream sensor if i'm not mistaken. The downstream sensor is what tells the car whether or not the Catalytic converter is 'below threshold' Best to actually scan the sensor readings like Peter mentioned above or just replace the downstream sensor
to answer both of you, back the code was P0314 after I replaced the sensor it worked for about 3 months and now the code is P0420. My question is if there was no carbon build-up or anything else that was sent to the catalytic converter back when the sensor was bad, how come all of sudden the CAT starts to go bad? after all a bad 02 sensor does not damage the CAT is I'm not mistaken. The car has like 158kms on it and should be working fine. As Thoiboi stated that it sounds like B2S2 now, I did check the voltage on the sensor and I believe the B1S1 upstream sensor was showing result negative while others were fine I will check again. Is it often that both the sensors can go bad again while B1S1 is almost brand new and B2S2 is old? I highly doubt its the CAT because I don't see rpm go up and down while on Idle however I see a change in gas mileage and a slight change in performance as well but if it's the CAT then what's next if I would not want to replace the CAT, if I go CAT less on B1S1 and leave the B2S2 with the CAT would it work that way or does it have to be CAT less from top to bottom?
I've seen cars with bad cats and low mileage. Some are replaced under the warranty. Usually that's due to people driving with misfires, engines consuming too much oil, or just cats being defective. From my limited experience P0420 is more often bad cat than bad sensor. Exhaust leaks might also cause that code. I think newer Toyotas are especially sensitive. However there is a small chance of exhaust leak between first and second sensor.
To be sure, you need to check. If you want to throw parts, sensor is cheaper and easier to replace.
Just to be sure we are on the same page:
DTC P0134: Rear A/F Sensor (Bank 1, Sensor 1) Heater System Malfunction - that's the first sensor, upstream, before the cat, on the rear of the engine.
DTC P0420: Rear Bank Catalyst System Efficiency Below Threshold (Bank 1) - that's the rear cat
If you want to throw sensor at it, you need B1S2, downstream bank 1 sensor, after the catalytic converter, rear of the engine.
What you mean by "showing result negative". There are 6 or 7 wires at the upstream sensor so which one you probed? Also checking voltage directly at the wideband AF sensor will get you nowhere. They are current output devices, and then ECM converts the measured current to "old style" voltage display. Probing the correct wires will yield voltage reading that will not change depending on how rich / lean engine is running. "Sensor ground" might yield like 2-3V if probed against chassis ground. The rear sensor (downstream, S2) is an old style "switching" sensor.
Defective cat that is not plugged won't affect engine performance. Plugged cat will limit performance, especially on the higher RPM. Really bad plugged cat might cause bank 1 misfires codes. Sometimes they can crack and piece of cat can lodge sideways limiting the exhaust flow. Enough to trigger the code, often not enough to tell by how the car feels. If not plugged, I would leave the cat alone as there is no point going catless.
To check the sensors, car needs to be at operating temp, and you need a scan tool. Generic $10 OBD scanners from Amazon might be too crappy to tell. I like to set the scan tool on record and drive steady at ~40-50mph for the test. Guy on the video just pressed throttle and that worked fine.
I've seen cars with bad cats and low mileage. Some are replaced under the warranty. Usually that's due to people driving with misfires, engines consuming too much oil, or just cats being defective. From my limited experience P0420 is more often bad cat than bad sensor. Exhaust leaks might also cause that code. I think newer Toyotas are especially sensitive. However there is a small chance of exhaust leak between first and second sensor.
To be sure, you need to check. If you want to throw parts, sensor is cheaper and easier to replace.
Just to be sure we are on the same page:
DTC P0134: Rear A/F Sensor (Bank 1, Sensor 1) Heater System Malfunction - that's the first sensor, upstream, before the cat, on the rear of the engine.
DTC P0420: Rear Bank Catalyst System Efficiency Below Threshold (Bank 1) - that's the rear cat
If you want to throw sensor at it, you need B1S2, downstream bank 1 sensor, after the catalytic converter, rear of the engine.
What you mean by "showing result negative". There are 6 or 7 wires at the upstream sensor so which one you probed? Also checking voltage directly at the wideband AF sensor will get you nowhere. They are current output devices, and then ECM converts the measured current to "old style" voltage display. Probing the correct wires will yield voltage reading that will not change depending on how rich / lean engine is running. "Sensor ground" might yield like 2-3V if probed against chassis ground. The rear sensor (downstream, S2) is an old style "switching" sensor.
Defective cat that is not plugged won't affect engine performance. Plugged cat will limit performance, especially on the higher RPM. Really bad plugged cat might cause bank 1 misfires codes. Sometimes they can crack and piece of cat can lodge sideways limiting the exhaust flow. Enough to trigger the code, often not enough to tell by how the car feels. If not plugged, I would leave the cat alone as there is no point going catless.
To check the sensors, car needs to be at operating temp, and you need a scan tool. Generic $10 OBD scanners from Amazon might be too crappy to tell. I like to set the scan tool on record and drive steady at ~40-50mph for the test.
The first time when the code was P0314 bad o2 sensor, it doesn't really tell that it's indeed the o2 sensor however I checked with the Scan Tool, and the voltage on the sensor was in negative that was I meant so was firm that its the sensor so I changed it and now when I checked I believe it showed the voltage in negative again, however, I just realized that when I checked the car wasn't running at a normal temperature as it was parked overnight and an entire day when I checked it this may have given me wrong readings however I will check again with the car warmed up to see if its the senor or something again. I just bought those adhesive Dura Lube Cata System Cleaner and put it in my gas tank and drove and parked, I will see if that makes any difference. Meanwhile, any other advice would be helpful thanks!
I don't believe in anything you put in a gas tank... well except fuel conditioners - those are fine (for long time storage, or diesel winter additives). Whatever you put won't hurt but most likely won't help.
P0314 is for the heater inside the sensor. Without the heater, af sensor doesn't work at all, so any reading obtained with bad heater doesn't matter. Voltage shouldn't really be negative. If scan tool displayed current, that can be negative (as 0 current is stoichiometric, and positive / negative varies on the manufacturer, but will mean either lean or rich). But then different scan tools display different values, and generic OBD display whatever.
You can compare how bank 1 and bank 2 sensors behave. Chances are bank 1 sensor 2 will be "switching" while bank 2 sensor 2 will be more steady. Downstream sensors might have same connectors / wire lengths so it might be possible to swap them before replacing the sensor.
Disregard any info about "switching" upstream sensor from the second video - I didn't notice at first but his car uses traditional oxygen sensors, not af sensors.
You cat might be at borderline, meaning that P0420 might not come back for a while after clearing the codes, giving you the feeling that cleaner magically helped. I've heard about people taking out cats and soaking them in something, but I never did that so can't say if that does anything.
OP you can stick a borescope into your cat when you have the O2 sensors out. If the matrix is clogged or you see "bacon bits", it's time to replace it.
11-02-2020, 11:33 PM
