Obd2 dtc p0420

My explorer 96 XLT 4.0 has had a DTC P0420 for some time now. Smog check is required in a couple of months, so I need to fix this by then...no money to take it to a mechanic for now.

We connected a borrowed OBD2 tool and retrived the following:

DTC P0420 Catalist System Efficient below Theshold (bank)

live data @ idle
Cal load: 28.4 %
STFT B1: from -7 to 10 (%)
STFT B2: from -7 to 10 (%)
Eng RPM: 800
Spark Adv: from 8 to 12
MAF(lb/min): 0.664
TPS: 18.8 %
O2S B1 S1: from 0.065 to 0.725 (v)
O2S B1 S2: from 0.065 to 0.67 (v)
O2S B2 S1: from 0.055 to 0.8 (v)

What information can we get from this data?

Also, per a mechanic comment, once DTCs are reset, the compuer will read it again after driving the truck around 35 miles. A couple of times this is exactly what I noticed, but the last time, when I had to clean the ICV due idle issues, erased the DTC again. But after that, the check engine did not came ON around the 35 miles, but after 100 miles..I wonder why...does this ICV has something to do with this?

Do we really need to replace the cat or O2 sensors?

Any help will be greatly appreciated

That code is telling you that you have a bad cat on the bank 1 side.

I would swap the 2 rear 02 sensors with each other and see if the code moves to the other side or not. It might just go away all together-

Disconnect the battery before you start the swap to clear the pcm.

1998Explodasport said:

That code is telling you that you have a bad cat on the bank 1 side.

Click to expand...

Not neccesarily. Could be a bad 02 sensor.

Turdle said:

Not neccesarily. Could be a bad 02 sensor.

Click to expand...

Ya you are right I just always think the worst.

If your code remains the same after swapping the sensors, it would indicate to me the cat converter was bad
if the code moves with the sensor-then the sensor is bad.

Getting to the connectors for the rear 02 sensors requires removing the center console. Do not be intimidated by this, it is easy.



http://www.explorerforum.com/forums/showthread.php?t=209770

you could try switching sensors but there are other options. I've seen cat codes also just go away (bad tank of gas?? IDK??).

The 96 OHV has computer software update at the dealer that will make the catalyst monitor less sensitive. This is a last resort before changing the cat, but if the cat is really dead it won't help. Keep that in mind.

A graphing scan tool (or even seeing live data) would give more insight, the S1 sensors should be switching quickly while the S2s switch very slowly. The computer divides the switch ratio and averages it over a few drivecycles, using an exponentially weighted moving average(giving the benefit of the doubt for a few bad readings).

If the cat fails the S1 switch rate = S2 switch rate, so the ratio is 1. If the cat is getting old, it gets close to 1.

So live data would tell you right away what is going on. The numbers for all the sensors look normal, but without seeing them in action you can't be sure (they may be slow to respond for example)

as already stated, its a bad o2 or a clogged cat.

O2S B1 S2: from 0.065 to 0.67 (v)

That 02 sensor is less than enthusiastic.

no data for 02 sensor 2 bank 2 though. I would like to see the comparison

Turdle said:

O2S B1 S2: from 0.065 to 0.67 (v)

That 02 sensor is less than enthusiastic.

no data for 02 sensor 2 bank 2 though. I would like to see the comparison

Click to expand...

What is a good reading for the rear O2 sensors?

Thank all for your fast reply.

I will definitively swap the sensors. The link provided is great

Just out of curiosity.

I have not check under the truck, but I was told this truck has 3 sensors. 2 before the cat (one per bank) and one after. With the info from OBD2, it is confusing now. Which sensors is which one? The ones before the cat should be B1 S1 y the other B2 S2? What about the one after the cat? S3?

Why the OBD tool gave me B1 S1, B1 S2, and B2 S1?

O2 sensor numbering

As I recall when there is only 1 post cat sensor it is numbered as bank 1 sensor 2. Obviously, if there is only 1 post cat sensor you can't switch it with one on the other bank. The SOHCs and I believe the later year OHVs have an H exhaust instead of a Y exhaust and have two post cat sensors.

You didn't post your LTFTs. Are they both 0%? Your mixture is slightly rich but not excessively.

The voltage range for the post cat sensor is a little low.