The check engine light on my truck just suddenly came on. Went to Autozone to check for codes and it comes up P0420. The description is pretty vague and a search doesn't really tell me much. If my research is correct it seems I should start with O2 sensor, then look toward cat. convertor. Strange thing is, I don't see any symptoms of anything wrong. It seems to drive fine. I'm tempted to think maybe I have some bad gas since I just filled up 2 days ago, pretty close to empty. Have some Lucas in it now. Some research also pointed to ethanol issues. I have some treatment that I have to use on my boat. Would this stuff be safe to use in my truck AND mixed with the Lucas? Any other easy stuff I could start looking at to work my way up? I'm handy, but no Mr. Goodwrench either. TIA.

EDIT: I'm hoping this was just a fluke. I replaced the air filter (needed to be done anyway) removed the negative battery cable and cleared the light. Drove around for a little bit and still no light. I'm really hoping it was just bad gas messing with the O2 sensors. Already had to replace this engine once because a faulty fuel injector caused it to hydro-lock and throw a rod. So I'd be EXTREMELY pi$$ed if there's something major there. Of course they didn't replace the cat or anything either. I'm at 74k miles now, with about 35k on the new engine.

 

The P0420 code means the passenger side cat is no good or the rear O2 sensor on the same cat is no good. Bad gas would affect sensor 1 not sensor 2.

 

Wouldn't it be more likely that the sensor would be bad than a cat for a truck this new/old? Not sure if it's the same thing you're referring to, but the printout for the error code said bank 1. The exact message is:

P0420 Catalyst System Efficiency below Limit - Bank No 1

It's the only code that registers and like I said, the truck is not exhibiting any issues at all. Performance is fine, gauages are all normal. I have some vague instructions on checking voltages, so that might be my next move if it happens again.

 

If the faulty injector was on the passenger side, then all of the raw fuel it was dumping went out the exhaust and into the cat. Misfires and raw fuel significantly reduce the lifespan of the associated cat.

FYI, bank 1 is the passenger side, or in fact in any vehicle, bank 1 is the side with the #1 cylinder. On our motors the #1 cylinder is the front most one on the passenger side, making that side bank 1. Sensor 1 is between the exhaust manifold and the cat. It's main function is to report back to the ECM the air/fuel mixture so the ECM can adjust it for peak efficiency. Sensor 2 is at the outlet of the cat. It's main function is to measure the efficiency of the cat itself. That's why a P0420 code means the passenger side cat is outside normal operating specifications, or the B2S2 O2 sensor is.

 

Depending on where you live, the cats are "probably" still covered under the emissions warranty. California 7/70, 49-states 8/80 is the norm for US owners.

Catalyst efficiency codes are an emissions item and usually have no bearing on the current operation of the engine; that is, there are no differences in drivability. Downstream O2 sensors do not cause efficiency codes as both the upstream and downstream O2 sensors are tested by OBDII prior to execution of the catalyst test. It is not uncommon for a misfire or faulty upper O2 sensor to flood the cat with fuel and shorten its lifespan as already noted. But, if the efficiency code reappears, it's a very good indication that the cat is no longer functioning as it should.

It takes two consecutive efficiency monitor self-tests to fail in order to set the MIL with a stored code. Since the self-tests do not execute every drive cycle, you will need to wait (continue to drive the vehicle) to see if the code comes back.

Frankly, unless you have to undergo a mandatory emissions test, you can postpone repairs (unless still under 8/80 emissions warranty). If you are still under your emissions warranty, let the Ford dealer properly diagnose it since they have the proper equipment.

See TSB 01-9-7 (https://www.ford-trucks.com/tsb/full...x.php?p=by_tsb) for background information and the 2006 OBDII manual (available at motorcraft.com)

 

Assuming something else, like a leaking injector, didn't cause the damage to the cat. It's a Federal mandate so the only location limitation is if your state has emission testing or not. Those that live in states that do, are covered.

http://www.epa.gov/oms/consumer/warr95fs.txt
"Specified major emission control components are covered for the first 8 years or 80,000 miles."

 

Now that I think about it, I think they replaced the cat when they replaced the engine because of the hydro-lock. Once you mentioned that a bell went off.

 

Put a running scan tool on it today. So far nothing shows up and the code is now P0000.

 

A P0000 code means the ECM failed to complete a self-diagnosis. Disconnecting the battery for 10 minutes or so will usually clear up that code.