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P0420, and rich bank 1

Aerohokie

Aerohokie

SM 2020
PM 2017
Full Member
Joined
Apr 16, 2006
Messages
249
Location
Pensacola, FL
2004 Z71 1500, 170k

Cruising around on the highway I popped a P0420. Truck behavior sometimes acts sluggish, other times not, but idle is smooth. I plan to swap #2 sensors, but rust is strong, so while the pb blaster soaks in, I wanted to see if anyone had an idea about my sensor readings. Using Torque, I have monitored the read outs today. O2 sensor 1x2 reads an almost constant 0.7v while 2x2 is 0.1v. The other oddity is the fuel trim. Bank 1 seems to be richer by close to a factor of 2. At idle bank 1 has a LTFT of -2.5ish while bank 2 is -5 ish. You can see the same behavior is STFT readings too.

Mileage isn?t horrible, average is 13.7 on 33s. Does the fuel trim reading mean anything? Until I swap the #2 sensors, I can?t rule out a sensor issue, but that wouldn?t explain the fuel trim.

What are your thoughts?

 
My 03 1500 has 140k. I started getting a p0420 every few hundred miles. Just assumed it needed a catalytic converter. Finally one day decided to put my Modis Ultra on it and check out the 02 Sensors. Noticed bank 1 would go down to zero occasionally. Ended up picking up a Bosch on amazon for like $25. Haven?t had a check engine light since. It?s def running bit rich if you?re running -2, fuel is being taken away, that?s a bit odd. May poss have an injector dumping a bit too much fuel. Look at the Pids on 02 senors on a scan tool and hit the gas, the graph should spike up rapidly. In my experience p0420 codes are usually catalytic converters about 75% of the time but every now and again its just a slow or intermittent 02 sensor. They?re pretty inexpensive, may just want to try that first.
 
STFT between -10 and +10 is considered normal. They should be closer but a 5 is nothing to be concerned about. Driver vs passenger will almost always vary a few points from each other.
 
Thanks. Do clogged cats cause a fuel trim issue? Just wondering about ways to identify a cat is going bad right meow. I have worked on cars with totally clogged ones and know the ultimate signs.

I hope to swap the sensors tomorrow.
 
bad cats:
rear o2 sensor is there to tell you when cat is done.
also noise underneath truck like rocks in a tin can rattling..
also extreme high temp on cat versus inlet pipe (use laser temp gun)

Many things on internent on how to check cats

PS in my mind if you replace one then replace both as they have pretty much seen the same exhaust unless you had a bad cylinder for many miles - Raw fuel (read extra rich mix) is what kills cats and makes the honeycomb get so hot it melts in to little lava rocks
 
Do not replace the 2nd O2 sensor just. It's just a diagnostic sensor and it should not cause the car to have rough idle or acceleration. It's just a diagnostic sensor for the P0420 code. There is probably another rich mixture problem like misfires, MAF sensor, coolant temperature, O2 sensor 1 or something likely, any other trouble codes?. I think that your problem here, is that there is a rich mixture and this is not caused by the 2nd O2 sensor as mentioned. So repair the rich mixture before the P0420.
Let me know if you need more help with the rich mixture.

Source trouble code: https://mechanicbase.com/trouble-code/p0420/
 
Opely said:
Do not replace the 2nd O2 sensor just. It's just a diagnostic sensor and it should not cause the car to have rough idle or acceleration. It's just a diagnostic sensor for the P0420 code. There is probably another rich mixture problem like misfires, MAF sensor, coolant temperature, O2 sensor 1 or something likely, any other trouble codes?. I think that your problem here, is that there is a rich mixture and this is not caused by the 2nd O2 sensor as mentioned. So repair the rich mixture before the P0420.
Let me know if you need more help with the rich mixture.

Source trouble code: https://mechanicbase.com/trouble-code/p0420/
Click to expand...

But it isn't running rich enough to cause a problem.
 
After researching, the fuel trim looks within normal range. I graphed the B1S2 voltage today and it was all over the place from .13 to .87 with a pretty fast cycle rate. As I understand it, an old O2 sensor would get slower, not faster. This waveform makes me think the cat is indeed bad, but not clogged yet because the truck still runs and idles normally. Essentially, I am in the window between no longer working and clogging.

So, I have read good stuff on Eastern Catalytic Convertors. Their catalog says 83166 fits and they are on RockAuto for $57-ish each. Does anyone have a different suggestion for a cat? My local shop charges $75 per side, so total repair would be about $280. That's not bad.
 
That?s a good deal for catalytic converters. Typically a cloggged cat would result in very little power because the engine can?t breathe so to speak. Like ygmn said, most likely the vehicle had a bad misfire or so to ruin the catalytic converter, all the raw fuel. But eh, I know its not uncommon for the cats to go bad on these things. I would probably go with the 280 for the cats. For that price I don?t believe you can go wrong.
 
The code P0420 means that the catalytic converter or several parts of it stopped working the way they should. This can happen due to a lot of reasons.
The oxygen sensor or both of them have failed or have been damaged.
One of the sensors isn?t connected properly so there?s a problem with the wiring.
The temperature sensor on the engine isn?t working properly.
There?s a damaged or leaking pipe in the exhaust system that is affecting its performance as a whole.
There are several holes or leaks in the exhaust system of your engine.
The oil inside the engine is contaminated or not clean.
You used leaded fuel instead of unleaded fuel as recommended for your vehicle.
The catalytic converter isn?t clean.
 
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