P0420 No I don't have a solution

Spring break here so I'm about to take a 3 day trip in a different car. This gives you guys and girls 3 days to figure out how to diagnose the P0420 problem.

Just kidding but I do need to start trying to figure out the solution to fix this code.

2003 3.4L. We don't have smog checks here so it doesn't seem to matter as the vehicle runs like a top. I would just like to have know that everything is working properly.

I've read through many if not all of the posts concerning P0420 and I know better than to start throwing parts at the problem. I have one of the Wifi OBD2 units and OBD Fusion installed on my iPhone. Today I started trying to sort out how to run down the problem.

I created a dashboard on the program that allows me to look at 02 voltage Bank 1 Sensor 1, Bank 1 Sensor 2, Bank 2 Sensor 1 and Bank 2 Sensor 2, and also Mass Air flow rate.

Q1. Bank 2 Sensor 1 and Bank 2 Sensor 2 always read 0.00. I think this is because these sensors don't actually exist. There are only 2 O2 sensors on this vehicle and I think that they are both Bank 1. Is this a true statement so that I can stop looking at B2 S1 and B2 S2?

Q2. Bank 1 Sensor 1 so far has always read 0.00. Does this seem normal?

Q3. Bank 1 Sensor 2 fluctuates. Mostly staying around 0.64 - 0.76 but occasionally as low as 0.12 and as high as 0.84. I only have a few minutes of viewing this at which point I decided that I needed to figure out what I should be looking for. Is it normal for this sensor to fluctuate? What parameters should be "normal"?

Q4. What other sensors should I monitor? As mentioned I'm also looking at MAF rate which has thus far stayed pegged on 0.5 or was it 0.05.

The truck is new to me last September. It drove fine for about 3,000 miles and then in December it threw P0420. I had it cleared but it came back and has been on now since late December. Again, it runs like a top but I'd like to have clear dash lights.

Thanks in advance. Remember, I'd like this fixed in the next 3 days.

 

I did not read all your post, but I had same problem. I had the code for over a year, changed o2 sensors,then rear converter. Still no fix. Finally had front converter changed during frame swap a month ago and all good.

 

If I remember I'll hook my scanner up this evening and see what I get for readings. Maybe that will reveal something.

 

there is a company that sells a device that plugs into the O2 sensor harness that fools the ecu into thinking that all is good. Illegal in most states as it is a defeat device. Do they have one to fit your application, dont know.

 

Q1 You only have bank 1 sensors 1 and 2.

Q2 No, but that condition "should" set a code. If it is not, that might be a hint. Look for open or closed loop operation as well, study up on that if needed.

Q3 Normal, but the ECU compares that "fluctuation" to the similar but faster fluctuation of the upstream sensor to determine if the cat is working. You have no upstream bank 1 S1 value. I would be looking/learning in that area for starters.

Q4 The rate should change with engine speed. I would still be looking into the missing bank 1 S1 signal, first.

 

I'm not keen on diagnosing the cats, but I had this code last year and needed to get it fixed to pass smog. Took it to Toyota and they told me they ran their tests on it and the front catalytic converter was bad (usually the 1st to go) and when that happens, the rear cat is not far behind it. So I needed to replace both.

OEM cats from Toyota are stupid expensive, over $1k each. I got CARB approved aftermarket ones through Magnaflow installed for around $600 at a local exhaust shop, code has been gone ever since.

If you don't need smog legal cats, then you can get even cheaper aftermarket ones than that.

 

Also, for the first few months I had this code my truck ran fine...seemed like nothing was wrong aside from the check engine light. However, after about 6 months the code would keep coming back more quickly after I would clear it, and I started to notice performance issues especially when the engine was under load (going up a long grade on the freeway, for instance). If it is the cats, they will continue to get worse and you'll start to notice it sooner or later

 

My OBDII reader recorded nothing for bank 1 sensor 1, bank 2 sensor 1, or bank 2 sensor 2. I don't mean 0 volts - I mean no reading at all.

For bank 1 sensor 2 I got readings ranging from 0 volts to .8 volts.

The MAF read from about 25 cfm up to about 800 cfm, depending on how hard I was stomping on it.

 

P0420 is like 95% the catalytic converter.
The only real fix is to replace it.

You have to figure out if your truck is California (50 state) emissions or just regular emissions.
Even though my truck was bought new in Maryland, and I bought it in MD...it was unfortunately a 50 state emissions truck. It's not really a big deal, it just makes things more expensive.

The code was saying "Catalytic converter below threshold". And the pipe flanges on my cats were pretty badly rusted, so I knew even if the cats were still good, they would be leaking a lot, which also throws the P0420 code.

I just bought everything from the Y-pipe back new off Rockauto. New pre-cat, cat, intermediate pipe, and muffler. It was like $450 shipped and I put it on myself. It fixed the issue and really quieted the truck down.


Also, there is a hack you can do the rear O2 sensor that will simulate a properly working catalytic converter to trick the ECU into thinking everything is okay.
You basically loop the signal wires together with a resistor and capacitor in between to create the sine wave function, but it didn't work for me.