CEL - advanced class

[nipper]

It was a dark and stormy night...

 

 

Actually a chilly and sunny day off roading. Going doena path which wasnt too bad at 20-mph left front wheel went over a washboard bunp-bump-bump-bump and lo the CEL did light. My inspection isnt due till next Dec so i wasnt excited.

 

i checked with the scangauge and it was our freind 420. Front O2 OE sensor (i didnt put it in) has 40,000 on it, rear has 10,000 on it.

 

Scangauge wont reset it.

 

i was fiddling with it today, and noticed when i stepped on the gas it was in closed loop, when i let up, it would go to open loop. This is instant. SO this tells me its not the cat (230,000 on the cat, 40,000 on the engine).

 

My thought. The front O2 sensor is physically damaged. It may be cracked and have an exhaust leak issue. The car is not loud, noisey etc etc.

 

Gas mileage has dropped more then it should for this time of year.

 

nipper

[njdrsubaru]

so i guess u have answered your own question, its the O2 sensor.. so whats the question?

[nipper]

so i guess u have answered your own question, its the O2 sensor.. so whats the question?

 

before i spend money i juat want assurance my thinking is correct

[njdrsubaru]

a 40K o2 sensor going bad is unlikely,, now the 420 code is a o2 sensor right? it can well be your cat converter, is it the original?

[nipper]

Not the cat because the cat wouldnt be instantly responsive to throttle poition. There would be a time delay, and it would not be going in and out of open loop closed loop all the time.

 

i am just hoping its not a cracked pipe.

[njdrsubaru]

sounds like it may be cracked then if everything else checks... crawl under there and look

[screwbaru2]

Sounds like your on track there nipper. I had a similar experience the other day when I hit a BIG puddle on the highway. CEL is on but I have'nt checked it yet. Seems to me water on a hot O2 sensor may cause problems.

[RallyKeith]

Not the cat because the cat wouldnt be instantly responsive to throttle poition. There would be a time delay, and it would not be going in and out of open loop closed loop all the time.

 

i am just hoping its not a cracked pipe.

 

I'm confused... What makes you think that the CAT has any effect on going open loop or closed loop and what time delay????? Front 02 sensor is monitoring cumbustion and the rear o2 sensor is monitoring the effeciency of the CAT. I'm about 99.9% certain going open or closed loop doens't have anything to do with the CAT or it's performance, only on the throttle position. That said I don't think that piece of information has any relevance to your situation. PO420 is catalyst effeciency out of range which is always a toss up of sensors or CAT. Given your circumstances I think it's even harder to gauge. Were the 02sensors OEM or aftermarket? If OEM I wouldn't expect them to fail, especially know what our rally car sees with no issues. But, at 230k the CAT has gone through a lot. I'm sure you're familiar with the honeycomb construction of the CAT. There is a chance some of it collapsed going over the bumps. If I had the time and resources I would probably pull apart the exhaust and inspect the insides of the cats, but that's me. Also, I would have someone else rev up the engine while I stood behind the car listening for any whistle coming from the tail pipe that might indicate a partially colapsed cat.

 

Those are my thoughts. PO420 is pain in the you know what to properly diagnose, so good luck.

[nipper]

I'm confused... What makes you think that the CAT has any effect on going open loop or closed loop and what time delay????? Front 02 sensor is monitoring cumbustion and the rear o2 sensor is monitoring the effeciency of the CAT. I'm about 99.9% certain going open or closed loop doens't have anything to do with the CAT or it's performance, only on the throttle position. That said I don't think that piece of information has any relevance to your situation. PO420 is catalyst effeciency out of range which is always a toss up of sensors or CAT. Given your circumstances I think it's even harder to gauge. Were the 02sensors OEM or aftermarket? If OEM I wouldn't expect them to fail, especially know what our rally car sees with no issues. But, at 230k the CAT has gone through a lot. I'm sure you're familiar with the honeycomb construction of the CAT. There is a chance some of it collapsed going over the bumps. If I had the time and resources I would probably pull apart the exhaust and inspect the insides of the cats, but that's me. Also, I would have someone else rev up the engine while I stood behind the car listening for any whistle coming from the tail pipe that might indicate a partially colapsed cat.

 

Those are my thoughts. PO420 is pain in the you know what to properly diagnose, so good luck.

 

 

I said the front sensor was supposedly OE. Open loop and closed lop has nothing to do with cat performance that is why i dont think it is a cat. The engine performance is fine, as is the load the the can gauge shows at given rpms/conditins.

 

I'll just go with my instinct then. i was hoping to find someone else who had a similar condition since money is tight, and i dont have a garage, and there is this cold white stuff all over the place.

 

nipper

[nipper]

Sounds like your on track there nipper. I had a similar experience the other day when I hit a BIG puddle on the highway. CEL is on but I have'nt checked it yet. Seems to me water on a hot O2 sensor may cause problems.

 

 

Thanks

 

nipper

[screwbaru2]

Nipper, was wondering how you made out with this? The CEL I mentioned in my reply is a P0141 the heater circuit in the #2 sensor is bad. I'm going to look at the sensor tomorrow PM see if there's actual damage. The CEL has come back 2x's now after clearing it so I'll be ordering one regadless what it looks like. Unless it's unplugged!

[nipper]

i was thinking about this, as the weather hasnt allowed me to get under the car. i am thinking its just what you said, the heater is damaged. Thats the only thing i can think of with instant open/closed loop response. My gas mileag is crap, so thats telling me its not the cat. Also if it was a cat i wouldnt get instant closed/open loop response whaen teh car is cold at 15 degrees.

 

I see that OE o2 sensor for blu is on sale at less then 100 bucks. i think i am going to order it on blind faith and my best guesstimate.

 

nipper

[kingbobdole]

Actually..

I'm thinking more the cat... how advanced is your scanner? Usually I'll just look at the front and rear O2 sensor readings... cruising down the road the front will be in pretty good flux, but the rear should be flat lined.

 

The P0420 you have is a cat efficiency code, not a heater code. Heater codes look at one thing.. continuity of the heater circuit and draw. This cat code compares the front and rear O2 readings... if they are similar, it sets the light.

 

You can be right though... a very lazy(faulty) front or rear sensor can also cause the code... but with the conditions you describe.. you probably just broke it...

 

Here's a quick test... while the exhaust is cold, lightly rap on the cat... If it sounds like a rattle, you need one:-\

[nipper]

My cat doesnt rattle. In all my years ive never seen a O2 sensor respond INSTANTLY to throttle by going closed/open loop, hence the damage theory. Also it got tripped over bad road which leads me to belive its a physical fault, not to mention it refuses to reset.

 

 

Also the 30% drop in gas mileage.

 

 

nipper

[screwbaru2]

Nipper, here's a few possible causes for p420. Number 2, 3, 5 and 6 has possiblites.

 

1.Leaded fuel was used where unleaded was called for

2.An oxygen sensor is not reading (functioning) properly

3.The engine coolant temperature sensor is not working properly

4.Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe

5.Retarded spark timing

6.The oxygen sensors in front and behind the converter are reporting too similar of readings

[nipper]

engine coolant temp is fine.

Engine timing is fine

 

2 and 4 are the only ones left really, and i dont think its 4, but its supposed to hit 60 here tomorrow so i may get a chance to look under the car and find out.

 

 

nipper

[nipper]

 

FINALLY

 

After a month i ran the scan gauge for the heck of it, saw the car was staying in closed loop much longer, scanned the codes, and finally got a reset.

 

Now for some odd reason, when i take my foot off the gas pedal, for a second or so the car will go open loop then back to closed loop, so i may still have an issue. It's not flipping back and forth constintly like it was.

 

I will warch to see what my next tank of gas does to see if my mileage came up or not.

 

nipper

[WoodsWagon]

Open loop and closed loop have nothing to do with the cat.

 

What open loop and closed loop is is a purely computational condition of the PCM. When the PCM is in "closed loop" operation, it is looking at the 02 sensor readings and adjusting the fuel injector duration (short term fuel trim). This is the mode it's in when you're under cruise or moderate load.

 

When you quickly open the throttle, the PCM switches to "open loop" operation, in which it decides the fueling of the engine based on tables and the MAF sensor. It runs the engine at a richer mix to make the power you're requesting, and throws concerns of emissions out the window for a short period. When you suddenly let off the throttle, the PCM goes in to engine braking mode, and fuel cut. With the injectors closed, The engine is 100% lean and the O2 sensor reading is pointless, so you're back in open loop.

 

The PCM will not switch from open to closed loop based on the condition of the O2 sensor. It switches based on load and operating conditions of the motor. Open or Closed only indicates if the pcm is using the O2 sensor as a feedback calculation or not.

 

Now, the P0420 catalyst inneficiency code has to do with the PCM watching the front and rear O2 sensors and calculating the amount of fuel the catalyst is burning. If the 02 sensors are getting lazy, then the data the PCM is using is faulty, and it can set the code. However, if the sensors get too lazy, then a sensor range performace code will set, not a P0420. So it's a small window in which the sensors are just lazy enough to make the cat look bad, but not lazy enough to set an O2 sensor code.

 

Your sensors are pretty new and the cat has 230K on it? I'd say the cat is probably done. The cat can loose it's effectiveness without clogging, they just wear out over time.

[nipper]

Well my gas mileage is back up, yay, and everything is fine.

 

i will keep an eye on it.

 

 

I cross my fingers because i cant afford a cat (though i actually like working on modern exhaust systems).

 

nipper

[Cougar]

Since the trouble code comes and goes quickly I have to think the problem is due to an electrical connection problem, with the rear sensor possibly.

[nipper]

Since the trouble code comes and goes quickly I have to think the problem is due to an electrical connection problem, with the rear sensor possibly.

 

i still may put it on the to do list. even with 23.00 a fill up thats 14 mpog was getting painful.