(Anecdotal)P0240 remarks & generic question

[Terkins]

I post these comments for others to ponder. I don't understand them; I just relate them.

[First: I'm terribly envious! I didn't even have to lie on my back or jack the car up to gain access! Everything was staring us in our faces under the hood. By-contrast: I still haven't located the O2 sensors on my Explorer...]

[Our son's 2007 Honda Civic was] throwing the infamous P0420 code on/off for several weeks. I convinced him to purchase a new upstream O2 sensor (175k miles) & a backpressure tester. My rationale: We had just replaced the spark plugs and the P0420 still kept reappearing. No other symptoms.

The backpressure gauge (upstream sensor position) didn't even register ANY obstruction. (No clogged catalytic converter or muffler or exhaust...)

Installed the new upstream O2 sensor. Old sensor had blackened tip indicative of a "rich" fuel mixture. P0420 code disappeared on startup. [BTW: Old (original) sensor broke loose without ANY effort. New sensor (NTK) was precoated with antisieze compound.)

Inquired if son's air filter was "due for a change"? "Yes"; 12k mi.. Replaced.

Could the dirty/clogged air filter have created a "rich" condition causing the black deposits on the old O2 sensor...and the downstream O2 sensor to register "malfunction" of the catalytic converter?

(I'll update if the P0420 reappears... Walker website posits that the newer O2 sensors--when installed solo/upstream--can cause the downstream sensors to trigger a code after 30-60 days?)

I'm tempted to replace my Explorer's 137k mi./18-yr-old upstream O2 sensors. Both NTK and Walker manufacturers recommend replacement >60k-100k mi. due to decreasing performance approaching failure. (Same reasons spark plugs are replaced; they're just cheaper to replace.) (Gotta wait for $$ until budget allows purchase.) I've been coached by members to purchase an OBDII reader (3rd one!) that will mate with FordSYS app to read misfires, etc. Meanwhile my doorlock switch went bad ($34.00). Thus the "used-Ford-train" "travels down the rails paved with dollars"!

As soon as weather/time allow, I think I'll hunt down my O2 sensors, remove-and-inspect for signs of wear. Most manufacturers advise against any type of cleaning action of O2 sensors...

[Wow! After listening to these two women, I guess I gave the son some good advice on replacing his O2 sensor! WALKER® EXHAUST SYSTEMS :: Check O2 (Oxygen) Sensor #NotMyWifesAdvice]

 

[boominXplorer]

I'm not one to argue but a p0420 code is a code for a bad catalytic converter usually. Honda o2 sensors do go bad often and it's usually the heater circuit that goes bad. Also most newer VTEC motors (say 01+) use wideband sensors in position 1 and are MUCH more sensitive / higher tech than ones found in most Fords until about 2008 or so.

 

[Terkins]

Honda o2 sensors do go bad often and it's usually the heater circuit that goes bad.

I was aware of the P0420 being a cat code. There are specific codes for the sensors; none were triggered. If the (upstream) O2 sensor was getting weak/crazy in function, the video (above) says it could screw up the air/fuel mix and make the computer feed a too-rich mixture (black soot on old O2 sensor tip?) Time will tell if the cat throws the code again...

 

[J_C]

Parts manufacturers are always going to suggest that you should replace your parts

They're going to tell you that old parts "can" do XYZ, and it's true, at some point parts wear too much but I wouldn't make a lot from what you observed. The older many things on the vehicle get, the more likely they "can" fail, but it seems like there has to be some limit on how much preventative maintenance to do on an 18 year old vehicle unless the repair just lends itself to ease because you have better access due to doing another concurrent repair.

Old part with exhaust on it for many years, sure it may have soot. Once it fails the engine will run richer to keep running.

Unless you find your fuel trims way off, or are putting a ton of miles on it so you expect to reap a little MPG savings, I'd wait. Then again if you're putting a ton of miles on, you might soon enough find something else needs fixed more than O2 sensors.

 

[1998Exp]

Inquired if son's air filter was "due for a change"? "Yes"; 12k mi.. Replaced.
Could the dirty/clogged air filter have created a "rich" condition causing the black deposits on the old O2 sensor...and the downstream O2 sensor to register "malfunction" of the catalytic converter?

Unless the vehicle is driven on very dusty roads, 12K is far from being "due tor a change". Most manuals recommend changing at 30K intervals. And I don't see how even a dirty air filter will create a rich condition - the MAF is still measuring the actual air flow. Just saying...

 

[Terkins]

...the video (above) says it [a failing, upstream O2 sensor] could screw up the air/fuel mix and make the computer feed a too-rich mixture (black soot on old O2 sensor tip?) Time will tell if the cat throws the code again...

...two weeks out, driver says his MIL hasn't re-lit/hasn't thrown any new codes.

 

[Terkins]

...two weeks out, driver says his MIL hasn't re-lit/hasn't thrown any new codes.

Three weeks out and the PO420 is on/off again. He went and bought a downstream O2 sensor replacement and wants help to install it. Meanwhile I'm busy moving and it's COLD outside!