Pending P0420 code after acceleration on highway

Status
Not open for further replies.
W

wing0

Joined
Oct 8, 2012
Messages
357
Location
Ontario, Canada
Today's pretty cold here around -15C+ with snowstorm and on top of that windchill.
I was on the highway trying to beat the after work traffic and tried to get ahead of a snowplow like all the other cars.
Dropped into 4th and accelerated while trying to avoid all the rock salt spray.
At this moment, while I was running over these stuff, my CEL came on. I went home and read it with Torque.
It's all muddy wet in the garage right now so I cannot get under the car to look at the the cat.

Pending P0420 code which means possibly something wrong with the cat.

Car is Honda with K20 engine with ~303000 km now. Never changed the O2 sensors.
As far as I know, there are 2 sensors B1S1 and B1S2. I cannot read the B1S1 voltage, but I can see B1S2 through Torque.
1. Is that normal?

2. Why all of a sudden this code pop up just because I did a bit more acceleration in the 4-5K rev range?

My cat heat shield is pretty rusted out with lots of holes, I have 3 hose clamps holding it together so there's no rattles.
3. Is a cat very easy to damage by road debris?
 
Spirited acceleration will increase the exhaust velocity. A Poor performing cat will often be okay at idle/cruise but at acceleration will not perform well if at all.
The method the ECM uses to determine if a catalytic converter is bad is to compare the forward voltage and number of 'switches' to the rear O2. The rear should switch less and have a lower amplitude compared to the front.
I dont know why torque cant see forward O2 voltage.
 
At that mileage I would do the rear o2 spacer trick if it continues but wait a bit. The efficiency is most likely down at higher flow rates as Colt said so it not dead just tired and in warmer weather it may be no problem, the snow and ice probably lowered the internal temp when it needed it most to catalyze the exhaust.
+1 Air fuel monitor aka wide band up front. JMO
 
I thought 420 means there's too much marijuana smoke in your car. Or is it possible to have too much?
laugh.gif
 
My recent Honda cold weather P0420 code experience may be of interest to you:

https://www.bobistheoilguy.com/foru...84/cat-codes-in-cold-weather#Post4988484
from that post:
Here's what I (think I've) learned.
They mean front and rear Cat performance under par.
It takes two failed runs in a row to throw the code.
They happen more often in cold weather.
They usually don't mean the sensors are bad, since the before-cat and after-cat O2 sensors have to agree in lock-step that the same amount of oxygen is going by.
Usually these codes mean it is time for new Cats.
Can be caused by intake leaks and diagnosed by fuel trims.
Originally Posted by wing0
2. Why all of a sudden this code pop up just because I did a bit more acceleration in the 4-5K rev range?

For the code to pop up, means that a.) the ECU has moved from open loop to closed loop because it expects that Cat to be hot and functioning after warm-up, and b.) before and after sensors are seeing the same pattern of oxygen going by. As the fuel trims and throttles vary, the sensed output of the Cat should be relatively flat, meaning oxygen seen by the first sensor gets burnt by the Cat before it gets to the second sensor. Instead the second sensor tracks the ups and downs of oxygen presence in lock step with the first sensor, and you get the code.
 
I know I sound like broken record but once you start getting P0420 occasionally, it will eventually become a permanent yellow light on your dashboard. The spacer trick is the only illegal work around. Don't bother changing the post cat O2 sensor. That would be the absolutely wrong remedy but hey, you learn that the stove is hot after getting yourself burnt.
 
With lack of diagnosis, IMO, you may want to change both o2 sensors and if it is still coding then you know the Cat is bad.

My brothers Sienna have similar issue, we changed all O2 sensors (4 of them).
The code still lingering for a couple of years and we know the O2 sensors are good.
So, finally, he gave up and replaced the cat (there are 2 cats), not cheap but it goes away.

In TX, we have emission test so if there is code, there is a big chance it will fail.
 
After ECM reset, I drove ~60km to work on the highway.
The cat B1S1 temp sensor got up to 790-800C and the B1S2 voltage reading was moving between 0.2 to 0.7V while I had the cruise control set.
Just waiting for EVAP system to be ready, all other systems are in ready state according to Torque.

"Can be caused by intake leaks and diagnosed by fuel trims."
How do I monitor fuel trim to see if there is any issues?

I haven't touched the air filter since 240k. I'll take a look when I get home.
 
Originally Posted by wing0
How do I monitor fuel trim to see if there is any issues?

Torque has them well hidden as LTFT and STFT (long term/short term fuel trim), add a gage and them go digging for them.

Once you can view them, there is some different opinions on the thread I linked as to how to interpret them.

My code has not come back (yet). If it only happens when short tripping in single digit cold weather, I can live with that for years.
 
Originally Posted by HangFire
Originally Posted by wing0
How do I monitor fuel trim to see if there is any issues?

Torque has them well hidden as LTFT and STFT (long term/short term fuel trim), add a gage and them go digging for them.

Once you can view them, there is some different opinions on the thread I linked as to how to interpret them.

My code has not come back (yet). If it only happens when short tripping in single digit cold weather, I can live with that for years.


Ah thanks.
I did a freeze frame on the pending code and it got the STFT(0%) and LTFT(-2.34%) numbers so the spread is within 5% tolerance as indicated on some websites.

I think this is pointing towards cat getting old and maybe O2 sensors, but I probably will hold out till spring time before doing anything about it as long as the light doesn't come back on.
Our premier got rid of the requirement to pass drive clean(emission test via OBD readout) in order to renew license plate so I could theoretically drive the car to the ground with the light on.
 
Originally Posted by wing0
Our premier got rid of the requirement to pass drive clean(emission test via OBD readout) in order to renew license plate so I could theoretically drive the car to the ground with the light on.

Wow.

When I was dealing with a bad ECU on the Dakota, I discovered I could drive forever with a CEL and a pending emissions test in MD. I just had to bring it in every couple of months to fail again. And again. Back in the day when I drove nothing but beaters, there were time limits.

After 2 tries of rebuilt ECU's I finally got a "good one" from the rebuild/resell service and got on with life. Worth it I guess versus paying 4 times as much for a new one at the dealer.
 
Back to the Cat, it will perform better in warm weather than cold, so if you want to plan on replacement versus code frequency, consider that.
 
Maybe through my fuel economy conscious driving, I lug 5th gear too much?
My average rev range on the highway is 3-4k though due to short gearing.

Will some italian tuneup help? lol
 
Here in CA, they do a visual inspection and check for those, but I've leaned that a combination of copper RTV, stainless steel foil, and a thin-gauge wire wrap to hold it tight against the sensor will accomplish the same thing, but be completely hidden from the outside once you screw the sensor back in.
 
Status
Not open for further replies.

Similar threads

H
P0420 - 05 Jeep Liberty 3.7
Replies
2
Views
340
Vitamin Yoda
Globalksp
Helping our Babysitter: Diagnosing from 14(!!!) Engine Codes 2012 Hyundai Velostar
2
Replies
29
Views
1K
Accent Abuser
R
Downstream O2 code.....then immediate US code after change?
Replies
6
Views
852
someonesomewhere
John105
emissions testing/issues with P0420
Replies
19
Views
2K
Skippy722
T
Car jerking on acceleration
Replies
19
Views
2K
tookien
Back
Top