is catalytic converter under 8 years/80K wanranty?

Yes, the catalytic converter should be covered by the 8 year/80,000 miles emissions warranty but the #2 O2 sensor probably is not.

It is my humble opinion that the after-CAT O2 sensor is bad, not the CAT itself. The CAT is notoriously reliable, the sensor is equally unreliable. Replace the sensor first, taking special care to inspect the integrity of the wire harness and connectors.

Since the catalytic converter is probably covered by the 8 year/80,000 mile emissions warranty and the O2 sensor probably is not covered, and since the cat costs a lot more than an O2 sensor, in my also humble opinion, the OP would be better off getting a cat covered by the warranty than paying for an O2 sensor that is not covered by the warranty. If the problem persists, then the OP can inspect and/or replace the after-cat O2 sensor.

The dealer is not going to replace the CAT under warranty if the sensor is toast. And, if they replace the sensor, they will easily get several times what the job is worth.

In the conditions described by the OP, my guess is that the cat is bad, that the dealership will replace the cat, and ask the OP to pay for an O2 sensor "just to be sure."

The #2 O2 sensor does not fail nearly as often as the #1 O2 sensor, probably because it is in a cooler environment than the engine compartment and because it is sticking it's sensor (nose?) into the cleaner exhaust stream exiting the cat than the #1 sensor.

When the engine is first started after a cold soak, the catalytic converter is not hot enough to do its job so the #1 and the #2 sensor are sending basically the same signal to the computer. After the cat is warmed up, #1 O2 sensor is still doing its rich-lean oscillation but the exhaust stream coming out of the cat should be clean so the #2 sensor should not oscillate as much. If the #2 sensor is still oscillating after the cat is warmed up and the ECU sees a "busy" signal instead of a "resting" signal, it knows that the cat is bad.

If the #2 O2 sensor was kind of bad but not bad enough to set its own DTC, you are more likely to miss a bad cat than say a cat is bad when it is not.

A bad O2 sensor can cause DTC P0420 but it is a lot less common cause of P0420 than a cat that is actually bad.

In a similar vein, but a different car -- entirely different.

I have a '95 Bronco that tells me intermittantly that the Bank 1 O2 sensor detects a Lean Condition. My check light may or may not come on in any given trip, and generally goes out after coming on if the trip is long enough. That is, the light will not always come on, and when it does come on it will go out again if the trip is long enough. If the light is still on when I park, it is always off the next time I start the motor, then it comes on after several minutes. If the light comes on, then goes out, it has never come on a second time in the same trip.

I'm convinced the Bank 1 O2 Sensor is on its last leg because the stuff that can contribute to a Lean Conditiion is generally not transitory -- if there is a real Lean Condition, then it will remain throughout whichever trip where the condition was sensed.

I just bought this truck, and it passed Calif. Smog twice in the last 90 days.

Would you be considering the sensor under these conditions, and whcih bank is Bank 1 on my Ford engine? I haven't got a Ford Book, but my Jeep book and a Motor Manual both suggest Bank 1 is the Left side, but somebody told me that Bank 1 is the Right side. Do you know anything about Ford motors?

I'm guessing that this truck does not have an OBD II system because the light is being extinguished before the correct number of OBD II drive cycles.

Under the conditions you described, I would check the O2 sensor for Bank 1. Bank 1 is the bank where Cylinder 1 is located (hint- check the firing order on the distributor if it has one)

To check the O2 sensor function, hook up a volt meter to the O2 sensor leads (it doesn't matter if you disconnect from the vehicle's wiring harness or not) and read the voltage coming from the O2 sensor connector. With the engine running above 2500 RPM, voltage should fluctuate somewhere between .1 volts and .9 volts two to five times a second if the engine is Throttle body and five to seven times a second if it is multi-port. If frequency of the fluctuations is not enough of the range is not enough, replace the O2 sensor.

My experience with Ford engines is not very extensive: '68 Mustang with a 302 - fast car, it ate tires. '74 Mustang - can't remember if it had a 4 or a 6 cylinder, it was a sloooow car, only kept it for a few months '75 Granada with 302 - drove it from the midwest to SF to my first day of work at brand T, it pinged badly in the mountains and ate an alternator and voltage regulator on the way, very comfortable car. '7? Maverick with a straight 6 - friend's car, I remember working on the car but I don't remember what for.

That's correct. It is OBD I. I bought the scan tool for it, so I can easily extract the codes and reset the computer.

Dude this is 2006 wonder its hard to remember what you did, around 30 years ago ;)

mike hunt

LOL! Although I've worked on a few cars here and there, most of them were Toyotas so I tend to remember the non-Toyotas ;-)