1997 V6 Po420

[Szyd]

I have a 97 XLE 3.0 with 130K. I have had a PO420 for years cant figure it out new cat new Y pipe no leaks. I can turn it off with scanner and it will stay off for somtimes a day and others a few minutes. I clear the code take it to Echeck it passes than back on the CEL till i need to Echeck. Well i am sick of it and would realy like any ideas.

THANKS FOR ANY HELP.

[Szyd]

Bumping this up

[Szyd]

I used the search fuction and found nothing with my problem.

[hill8570]

Originally Posted by Szyd

I used the search fuction and found nothing with my problem.

Search for P0420, not PO420 -- there's quite a few threads in the forum related to that CEL. And good luck -- P0420 is probably one of the gnarliest codes to get to the bottom of.

[73sport]

P0420 Catalyst System Efficiency Below Threshold

After the engine is warmed up and the vehicle driven for 5 min. at 32 – 80 km/h (20 – 50 mph), the waveforms of the heated oxygen sensors, bank 1, 2 sensor 1 and bank 1 sensor 2 have the same amplitude.

That's from EG2.PDF

At a glance it almost reads as if the manifold sensors read 123XYZ, the exhuast traveled through the catylitic converter and still read 123XYZ with no change as in the CC did not have an impact on the exhaust gases.

I say you need a live computer read on this and look at the O2 sensor values and grab the freeze frame data.

With that you can see stuff like this and hopefully get a glimpse into why this has been happening. This picture of the scan software does not show sensor #2 past the cat in the graph but my goal here it have you get it to someone who can look at it at this level so they can see something more than the code itself.

Have any of the O2 sensors been replaced? Do you run consumer grade pump gas? There are a lot of things to "suspect" but we need more information.

Mr Hill, please chime in on this, but if he unplugged one of the engine O2 sensors AND recorded the voltage at the cat sensor, would this tell us if the cat is working effectively? This is for a short test run only. If the cat doesn't raise in temp to burn the extra fuel then I'd say that new cat is not working properly.

How is the engines performance? Does it run good, make good power, accelerate well? I think you'll need a computer and software to make quick work of this. . .

Regards,
73

[Szyd]

Thank you very much for youre input. It has been to the dealer and scanned and all they told me was it needed a cat. So i took it to a speedy or a munroe cuz of cost had them put a far infirior Y pipe and cat on. The light was out for a few days and than back on found a leak fixed it it was out for a few days than back on. Took it to a privateley owned exhaust shop where the guy let me get under with him and inspected the whole system for leaks nothing.

I have never reaplace the 02 sensors. I thought a bad sensor would throw another code all together.

[73sport]

I'm not going to say your sensors are bad, but I have to wander why the cat went bad to begin with? Mines a 95 with 220,000 miles and is original.

The upstream O2 sensors are very critical and they can be in pretty bad shape before they actually trigger their own codes. Something led to the demise of the old cat and that could easilly be the sensors.

Again, I suggest getting recordable data from scan software (likely a laptop) from a cold start to operating temperature. With this, you have information to make better "guesses" in this case. Specifically you need to monitor the details (like those in the picture above), not just the error codes. The voltage output from all three O2 sensors under varying load conditions would be very benefical towards sloving this problem. As shown in the pictures above, the sensor response time can be very different and not cause CEL's but impact performance of the system.

Can you answer the questions above?

[hill8570]

Originally Posted by 73sport

Mr Hill, please chime in on this, but if he unplugged one of the engine O2 sensors AND recorded the voltage at the cat sensor, would this tell us if the cat is working effectively? This is for a short test run only. If the cat doesn't raise in temp to burn the extra fuel then I'd say that new cat is not working properly.

Hard to view an oxygen sensor output with multimeter...it switches too fast if it's working right. Really need to have a real-time look at the output of the upstream and downstream oxygen sensors. By far the easiest way is with a computer hooked to the OBD port, like what you are showing. IIRC, the Federal emissions (I'm assuming a rig in Ohio is probably Federal emissions) 1MZ has two upstream sensors, a single cat, and a single downstream sensor, and P0420 is triggered when the downstream sensor (B1S2) "follows" the upstream Bank 1 (B1S1) sensor. Seems like a bogus way to do things, since I could visualize Bank 2 doing something to overload the cat (say, running rich), and you'd probably never get a diag unless that bank ran up against the "system too rich" DTC. Wordy way of saying I'd want to see a realtime plot of B1S1, B2S1, B1S2 and the freeze frame from the DTC before I could even begin to make a guess.

[73sport]

^^ Easy to see I was unclear there. Never mentioned a DMM though. I was referring to scanning software and laptop as I had all along. A multi meter would be of no help here. Agreed.

From above:
I say you need a live computer read on this and look at the O2 sensor values and grab the freeze frame data.

Originally Posted by 73sport

. . .

Again, I suggest getting recordable data from scan software (likely a laptop) from a cold start to operating temperature. With this, you have information to make better "guesses" in this case. Specifically you need to monitor the details (like those in the picture above), not just the error codes. The voltage output from all three O2 sensors under varying load conditions would be very benefical towards sloving this problem. As shown in the pictures above, the sensor response time can be very different and not cause CEL's but impact performance of the system.

. . . .

I hope this clear things up. . .

[MrKrispy1183]

Clean your mass air sensor and reset the battery. A dirty sensor/significant change in airflow will signal the ECU to run richer, triggering P0420. This happened to me recently; shady mechanic managed to get me to replace main cat and tried to get me to replace both pre-cats (CA-spec) as well. Wasn't having it, and consulted my friend/current mechanic GregTRD from SolaraGuy. Was told to check/clean O2 Sensors, but first to clean air sensor and reset ECU. Light hasn't come back on since.

[Szyd]

I run regular pump gas never reaplace sensors.
I will have to find a shop to take the time and realy do a throw diagnostic on it. Mean while i will clean the Mass air sensor.

There probably was nothing wrong with the OE I just took some body at the dealers word. They are suposed to be the experts that is why i took it to them in the first place.