whatiswrong?

Hey friends,

I have a 2000 accord LX that has given
me a P0420 DTC. Apparently this
means my cat is done for. I searched
on Google and found out if you pound
the cat and it rattles than its for sure
the cat is broken. I went under and
sure enough it had a rattle sound but I
have no idea what an unbroken cat
sounds like when pounded so I have
nothing to compare it too. I also had
my brother used his scan gauge to test
my o2 sensors. My o21/1 is running
rich, which is probably why my cat failed and
my o21/2 is going up and down just
like it shouldn't. Me and my brother are
no experienced mechanics so we are
just doing what we learned from our
research.



Around 17:48:36 is when I started the car and ran the RPM at 2k for 10 seconds or so.

Also, here is the freeze frame data if it is any help:
Vehicle Calibration ID: AAL740.......... Freeze frame information:
------------------
Fuel Status = 0 byte
Engine Coolant Temperature = 197.6 °F
Fuel Trim Bank 1 Short Term = -14.062 %
Fuel Trim Bank 1 Long Term = -6.25 %
Intake Manifold Pressure = 4.641 psi
Engine RPM = 1,299.25 rpm
Speed (OBD) = 33.554 mph
Intake Air Temperature = 125.6 °F
Throttle Position(Manifold) = 13.725 %

End of report.

I was wondering if I could get some
advice from someone experienced on
what all of this data means.

Thanks!!

MAD_MIKE

P0420 does not mean the catalyst is dead, is simply states 'catalyst below threshold efficiency'. If the engine is out of tune it can set the P0420 code. Banging on the catalyst is not a good idea as it has a ceramic substrate. Only way to check if a catalyst is non functional is to use an infrared scanning thermostat to see if there is a temperature change in the catalyst from the rest of the exhaust.

Find out why your car is running rich and fix it. With no rich/lean switching and stuck on rich the catalyst can only do so much.

Check the basics, air filter clean, fuel pressure within spec, spark plugs/ignition up to snuff, valves adjusted, ignition timing correctly set, compression check, TPS voltage input/output correct, MAP sensor input/output voltage correct. Etc etc.

Catalyst is a secondary system, find out the fault in the primary(engine) system that has lead to the P0420 code. Don't replace it on a whim, verify it is actually damaged/dead first. And even then, don't replace it until the primary cause has been resolved.

whatiswrong?

Hey MAD_MIKE,

thanks for your reply

My brother just tested out my o2 sensor using his scan gauge today.

He manually induced a lean environment by pulling out the PCV valve and letting it idle.

My o2 sensors did not react to the change at all. Could it be my o2 sensors are fried?

Here are the results.



As you can see my o2 1/2 is fluctuating wildly. If my engine was running rich then my o2 1/2 should be stable around a rich reading voltage, would it not?

And I am sorry for asking this newby question but, what is TPS voltage?

Thank you for looking!

slowcivic2k

Your sensor 1 looks a lot like a normal sensor 2, and vis versa, probably just a coincidence.

Your long term fuel trim is removing fuel from the vehicle, possibly because sensor 1 is biased in a rich state. The reason I can jump to that conclusion is because your rear sensor is swinging through the voltage ranges like a front O2 sensor would. (It's not supposed to be doing that, but the front and rear sensors are no different in terms of voltage range, sensitivity, etc.)

Unfortunately this wild swinging on sensor 2 means the converter is not scrubbing the exhaust like it should, and will require replacement. The sensor 2 data also tells us that you are still in complete fuel control from a PCM perspective. I would start by replacing the front O2 sensor and recheck. Drive the car until a good LTFT and STFT are known. Given your maintenance as an assumption, you should not deviate much from +/- 2%. (+/- 10% LTFT will set a rich code in most vehicles mind you.)

If your sensor 1 O2 cycles after replacement, replace the converter. Sensor 2 is perfectly fine, as long as you can get it out of the exhaust.

To answer your last question: Yes, it should be stable, but at a higher voltage. Since it is not, and is swinging like a front sensor, the converter is not scrubbing the exhaust.

whatiswrong?

Hi slowcivic2k,

I wish I read your post sooner. My car was due for a smog check so I jumped the gun and got my cat replaced.

I will definitely check the status of my o2 sensors and LTFT and STFT, bank 1 presumably.

I'll stay updated!

Thank you so much for the advice!

slowcivic2k

You didn't jump the gun, there was no doubt you required a converter. The question is, is your front O2 sensor biased rich. I say yes to that. You'll be buying a converter prematurely if you don't replace it.

whatiswrong?

Ok, thank you for the heads up. I'll be sure to do check my o2 first next time.

I did another round of testing and my cat seems to be scrubbing exhaust, my o2 1/1 is still running rich, and my stft is trimming alot of fuel, hits the 10% mark 2x.



o2 1/1 running rich, o2 1/2 scrubbing better than before but still seems to be struggling




stft 1 @ 2.5k RPM




stft 1 @ idle



I told my brother everything I learned from your advice, obviously I need to replace my front o2 sensor but he said my engine is running rich because of loss of compression from worn valve seals or piston rings so my Accord has to dump more fuel into my cylinders to create a "bigger explosion," so to speak, to make up for the loss of compression and he suggests that I get my engine rebuilt.

Needless to say, I'm afraid for my car and wallet right now.

Is what he saying advisable?

Thank you!

DCFIVER

The question that should have been asked is,is this a California emissions vehicle? Is it SULEV?

whatiswrong?

Hi DCFIVER,

Yes this is a California emissions vehicle and yes it is ULEV.

DCFIVER

In that case you have an AF ratio sensor,not an O2 sensor,in front of the cat. AF sensors need to be measured in miliamps in order to see amplitude swings in response to rich or lean conditions, you cannot use volts.
Your brothers "scanner" app is displaying the readings in volts and it is displaying the readings incorrectly.



Short term fuel trim is a direct correlation to AF ratio or O2 sensor readings. STFT can be used in lieu of AF or O2 readings to gauge the PCMs response to rich or lean conditions

Causing a vacuum leak on a MAP based vehicle will NOT cause the vehicle to run lean,nor will fuel trims be affected.

Simply drive the vehicle and monitor the STFT. If they are oscillating between -5 to +5 then the AF sensor is working fine.


OBD 2 PCMs contiunously monitor AF and O2 sensors. If the sensor was biased rich,it would set a DTC.





Assuming the data you posted is correct,the vehicle is running rich, and this will adversely affect Catalyst function.

whatiswrong?

Hey DCFIVER,

Thank you for your insight. I used my brothers scanner and took a short trip going about 30-40MPH to the grocery store and back home going 15-25MPH.

Here are my results:



30-45MPH




15-25MPH


According to my calculations and personal research, my engine seems to be running rich since its hitting the low 20's negatively, but I am not that mechanically inclined so I do not know if this is normal for Accords or not.

If it isn't, then I will follow MAD_MIKE's prognosis:
Also, according to aa1car.com, they suggest



I have also been noticing my tank seems to be emptying more quickly than before, but I have not officially been keeping track of my MPG to say for sure.


Also to note, my CEL has not come back on.



Now, I am a broke, full-time college student so I do not have the money to take my car to a professional mechanic and I barely have any time as it is, so if you men of knowledge can help me narrow down what I have to do then that would be much appreciated.


Until then, I will do the best I can with what I know and with what I have,


Thank you for reading!


-whatiswrong