02 sensor/P0420 problem

[Ardent]

Mr T gives a range of 11 to 16 when measured at 20 C.
If its out of spec, Mr T says replace. As per his manual.

[thetyrant]

Though most of the things have been mentioned, let`s see if anything is missed.
According to the manual, the P0420 trigger is: After engine and catalyst are warmed up, and while vehicle is driven within set vehicle and engine speed range, waveforms of oxygen sensors (bank 1 sensor 1 and bank 1 sensor 2) have same amplitude (2 trip detection logic). Which if accurate, narrows the problem down to two sensors. However, I kind of doubt based on their troubleshooting guidelines.

1. Check for air leaks. Especially, since you have a new catalyst, the cat itself should be the last resort.
2. Check oxygen sensor resistance. This is one health status indication, but unfortunately does not guarrantee proper dynamic response, that we care of.
3. Use Torque. One of the important things is to ensure ECM has completed oxygen and catalyst control routines. To do so, use the DTC display and check the status. You will be surprised, how long it might take to complete them, even if you drive it daily...
4. Do the Toyota troubleshooting. Again use torque, but this time remove every display and graph apart from the voltage of the three oxygen sensors (the latter to ensure maximum refresh rate). As per MrT procedure:
(a) In our case use Torque to monitor the three voltages.
(b) Start the engine and warm it up with all the accessories switched OFF until water temperature is stable.
(c) Race the engine at 2,500 – 3,000 rpm for about 3 min.
(d) After confirming that the waveforms of the heated oxygen sensor (bank 1, 2 sensor 1 (OX1A, OX2A)), oscillate around 0.5 V during feedback to the ECM (at a constanst engine speed of about 2500-3000rpm), check the waveform of the heated oxygen sensor (bank 1 sensor 2 (OX1B)). If there is a malfunction in the system, the waveform of the heated oxygen sensor (bank 1 sensor 2 (OX1B)), is almost the same as that of the heated oxygen sensor (bank1, 2 sensor 1  OX1A, OX2A)).
So you would expect a slower response rate on the post-cat sensor.
Hopefully, the above will help narrow the problem down.

Thanks for that and pretty much what ive been doing last few days so glad to hear im on right track, ive done a fair bit of research to try and work out the waveform and voltages I should be seeing on the post-cat sensor and as you say should be much less variable than the pre-cat sensors cycling up and down, what I find strange on my car is that the post-cat sensor does a bit of fairly static voltage at idle and steady revs like it should (although I see both low and high voltages which is odd!) but also sometimes does the same quick cycling that you get with pre-cat!, to me It points to the cat not being 100% efficient in its clean up of gasses but im still monitoring and yet to get on the mot emissions machine to see what that says.

I will take a couple of screenshots from Torque app running showing whats going on.

I did check and gap plugs and cleaned the maf on sunday which seems to have made a slight improvement in smoothness of car so maybe I had a mild misfire throwing fuelling out, ive not had cat error again since but haven't had a decent run out in car yet either so will get that done.

Ian

[deviantmr-s]

Though most of the things have been mentioned, let`s see if anything is missed.
According to the manual, the P0420 trigger is: After engine and catalyst are warmed up, and while vehicle is driven within set vehicle and engine speed range, waveforms of oxygen sensors (bank 1 sensor 1 and bank 1 sensor 2) have same amplitude (2 trip detection logic). Which if accurate, narrows the problem down to two sensors. However, I kind of doubt based on their troubleshooting guidelines.

1. Check for air leaks. Especially, since you have a new catalyst, the cat itself should be the last resort.
2. Check oxygen sensor resistance. This is one health status indication, but unfortunately does not guarrantee proper dynamic response, that we care of.
3. Use Torque. One of the important things is to ensure ECM has completed oxygen and catalyst control routines. To do so, use the DTC display and check the status. You will be surprised, how long it might take to complete them, even if you drive it daily...
4. Do the Toyota troubleshooting. Again use torque, but this time remove every display and graph apart from the voltage of the three oxygen sensors (the latter to ensure maximum refresh rate). As per MrT procedure:
(a) In our case use Torque to monitor the three voltages.
(b) Start the engine and warm it up with all the accessories switched OFF until water temperature is stable.
(c) Race the engine at 2,500 – 3,000 rpm for about 3 min.
(d) After confirming that the waveforms of the heated oxygen sensor (bank 1, 2 sensor 1 (OX1A, OX2A)), oscillate around 0.5 V during feedback to the ECM (at a constanst engine speed of about 2500-3000rpm), check the waveform of the heated oxygen sensor (bank 1 sensor 2 (OX1B)). If there is a malfunction in the system, the waveform of the heated oxygen sensor (bank 1 sensor 2 (OX1B)), is almost the same as that of the heated oxygen sensor (bank1, 2 sensor 1  OX1A, OX2A)).
So you would expect a slower response rate on the post-cat sensor.
Hopefully, the above will help narrow the problem down.

My notifications do not seem to be working, as this has progressed quite a bit...

I have rechecked for leaks along the system... none. I followed MrT's checks of the sensors and replaced b1,s1. I will be running torque later today to check the results.

[thetyrant]

My notifications do not seem to be working, as this has progressed quite a bit...

I have rechecked for leaks along the system... none. I followed MrT's checks of the sensors and replaced b1,s1. I will be running torque later today to check the results.

Interested to see your findings with the new sensor and everything warmed up, i watched mine closley on drive to work today and cat seems to be doing its job at idle ok with a fairly steady 0.6/0.7v reading from post-cat 02 sensors, similar when cruising around 2000/2500 revs as well, however when sat stationary at those revs it seem a bit all over the place but still no ecu errors logged so far so maybe cat was a bit dirty and with plug gapping/maf cleaning ive made engine burn a bit nicer and give cat less to clean up, i dont think the oem cat is so fussy and no doubt a much higher quality unit but then it should be at the price!

Took a couple of screenshots of torque running at various points and will upload tonight when im home.

Will keep monitoring and get the mot emissions checked before my test which is due in September, maybe i will need to fix the flexi on my oem cat to get through test!, we will see.

[deviantmr-s]

Excuse my ignorance on the sensors, learning as I go...

After 25 mins still the cat check is incomplete (attached) and two readings(screenshots) from the sensors also attached.

Voltages checked afterwards:

2,1 = 15.6
1,1 = 22.5
1,2 = 16.7

Advice please for a novice to sensor reading, thank you.

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[deviantmr-s]

Also, can someone explain the below please to me?

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[thetyrant]

Excuse my ignorance on the sensors, learning as I go...

After 25 mins still the cat check is incomplete (attached) and two readings(screenshots) from the sensors also attached.

Voltages checked afterwards:

2,1 = 15.6
1,1 = 22.5
1,2 = 16.7

Advice please for a novice to sensor reading, thank you.

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Doesnt look like your cat is working on that from what i can see as all 3 of the 02 sensors are cycling up and down, which is normal/good for x2 pre-cat sensors ( and post cat until warmed up) but the post cat should be a fairly steady line/voltage once cat is upto temperature if the cat is working as it should be, i get similar with mine then it goes steady when left to idle for awhile and will upload screenshot later.

Ian

[shnazzle]

Indeed. That is a knackered cat. 
Could try some cataclean and an Italian tune-up and see what the readings say but it's not looking promising.

[thetyrant]

Heres a couple of screenshots from my Torque data today, post cat is bottom left graph and needle gauge above it, top 2 are the pre-cat 02's, weirdly this morning it looked ok with steady voltage around 0.6/0.7v which i beleive is ok ? also no Error codes or EML, driving home after lunch today the voltage didnt look so good with lot of post cat 02 fluctuation even once warmed up, finally settled to steady low voltage 0.1/0.2v and when i scanned for error P0420 was back! ....

Morning data with cat appearing to work ?


Afternoon data with cat doing strange things...


Stupid car!

[shnazzle]

Heres a couple of screenshots from my Torque data today, post cat is bottom left graph and needle gauge above it, top 2 are the pre-cat 02's, weirdly this morning it looked ok with steady voltage around 0.6/0.7v which i beleive is ok ? also no Error codes or EML, driving home after lunch today the voltage didnt look so good with lot of post cat 02 fluctuation even once warmed up, finally settled to steady low voltage 0.1/0.2v and when i scanned for error P0420 was back! ....

Morning data with cat appearing to work ?


Afternoon data with cat doing strange things...


Stupid car!

Steady low voltage is still no good. It basically means it's running too lean for the cat to be effective. Hence p0420. 

Perfect would be stft1 and 2 fluctuating between say 0.6 and 0.3, with 0 LTFT and post-cat flatlining slightly above 0.45v.
So, make your call based on how far you are from that
Factors are:
- aged o2 sensors
- leaking injectors 
- dirty maf 
- dirty air filter
- fouled sparks
- intake (vacuum) leak (lean condition)
- exhaust leak
- oil burning
- and probably a couple more that I'm forgetting

[thetyrant]

Steady low voltage is still no good. It basically means it's running too lean for the cat to be effective. Hence p0420.

Perfect would be stft1 and 2 fluctuating between say 0.6 and 0.3, with 0 LTFT and post-cat flatlining slightly above 0.45v.
So, make your call based on how far you are from that
Factors are:
- aged o2 sensors
- leaking injectors
- dirty maf
- dirty air filter
- fouled sparks
- intake (vacuum) leak (lean condition)
- exhaust leak
- oil burning
- and probably a couple more that I'm forgetting

Indeed the steady low voltage has me most stumped!, and the fact its not doing it all the time!... i must get my wideband stuck in tailpipe see what that shows with the AFR so know what mixture is actually like, ive done a few things on your list as below..

- aged o2 sensors - Post cat is new denso, 1 pre-cat is about 6months old denso, other precat couple of years old looking at previous history and all seem to cycle ok.

- leaking injectors - dont think ive an issue here but getting them cleaned/checked is an option.
- dirty maf - cleaned this at weekend, did seem to improve running a little but maybe placebo
- dirty air filter - its pretty new
- fouled sparks - had plugs out looked ok but bit light which is expected it its lean.
- intake (vacuum) leak (lean condition) - cant see anything obvious checked clamps tight etc on pipework, will maybe pull it all off and go over it, car runs well enough though so dont think its that.
- exhaust leak- pretty sure there isnt one been over it closley
- oil burning - doesnt use any noticable amount of oil, think ive put 0.25litre top up in 4k miles since change


Car runs very well and if it wasnt for the P0420 i wouldnt think there was any issue!

Open to other ideas!

[shnazzle]

What are your long term trims like across the rev range? 
Digital voltages display doesn't really help much as it fluctuates so much and our OBD2 speed is so slow. 

I show;
STFT 1 and 2 (graph) 
LTFT 1 and 2 (graph) 
O21x1 (graph) 
O22x1 (graph) 
O21x2 (graph) 
TPS (bar) 
MAF (dig) 
Coolant temp (dig) 
Intake temp (dig) 
Fueling status (dig) 
Misfires (dig) 

If you really want to go nuts, I built a handy spreadsheet where I can copy-paste logged values and it creates a nice table so that I can see exactly what my LTFT is across tps and rpm range. 
Helps narrow down where thr car is over/under fueling. Very handy for mapping purposes on piggyback, and diagnosis. 
I.e. If it runs lean at idle (lots of + LTFT in idle range) but fine/rich unser load; probably vacuum leak. Etc

[thetyrant]

I will get some more data for you on the trims but they are all pretty low corrections from what i remember when i checked the other day.

[deviantmr-s]

Indeed. That is a knackered cat.
Could try some cataclean and an Italian tune-up and see what the readings say but it's not looking promising.

Already had two lots of cataclean through it, maf cleaned, filter changed, not burning oil and no leaks anywhere, been over it with a fine tooth comb yesterday. Oldest sensor is 3 years old.

About to take it out to graph again. Will try and take screenshots and post later.

[Carolyn]

Are the sensors all Denso?

[thetyrant]

What are your long term trims like across the rev range?
Digital voltages display doesn't really help much as it fluctuates so much and our OBD2 speed is so slow.

I show;
STFT 1 and 2 (graph)
LTFT 1 and 2 (graph)
O21x1 (graph)
O22x1 (graph)
O21x2 (graph)
TPS (bar)
MAF (dig)
Coolant temp (dig)
Intake temp (dig)
Fueling status (dig)
Misfires (dig)

If you really want to go nuts, I built a handy spreadsheet where I can copy-paste logged values and it creates a nice table so that I can see exactly what my LTFT is across tps and rpm range.
Helps narrow down where thr car is over/under fueling. Very handy for mapping purposes on piggyback, and diagnosis.
I.e. If it runs lean at idle (lots of + LTFT in idle range) but fine/rich unser load; probably vacuum leak. Etc

Not sure how much use this will be but logged trip home after work and uploaded to datazap, resolution is poor though due to slow obd port but trims don't look so bad from what I can see ?

Link to log here - https://datazap.me/u/thetyrant/log-1563899984?log=0&data=2

Ian

[deviantmr-s]

Are the sensors all Denso?

Yes all Denso.

[deviantmr-s]

Journey just taken and a map view of 1,2 sensor.

Is my cat definitely gone then?

[Carolyn]

Run it in to your friendly local MOT people.  Give them a tenner.  See if it passes... Then you'll know if it's the cat or the sensor.

[shnazzle]

The post-cat o2 readings are mirroring the two others.
I.e, the cat is doing nothing. Whatever its taking in is coming out. 
Cat efficiency being shit doesn't perse mean non-passing emissions mind. It is possible to pass.

[Carolyn]

In my experience, 1ZZs with duff cats don't pass emissions tests.

if the car passes an emissions test, then, is there a problem?

[shnazzle]

In my experience, 1ZZs with duff cats don't pass emissions tests.

if the car passes an emissions test, then, is there a problem?

Nope. But if it's running consistently lean, it'll fail on lambda. 1.03 is easily reached. Which would be annoying

[potge]

Also, can someone explain the below please to me?

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You can find more information in this Link

[potge]

From memory, the post-cat sensor is located on the cat assembly itself. Is there any chance that the aftermarket location is on a poor point?
Though this might also mask any underlying problems and make the car run improperly, have you tried a non-fouler?

[deviantmr-s]

Run it in to your friendly local MOT people.  Give them a tenner.  See if it passes... Then you'll know if it's the cat or the sensor.

Will take in for a test and see what transpires, thank you.