guiseppewv

So, my gf's car (2000 Corolla) had the check engine light on. I know the issue is at least one of the following:
1) Exhaust leak
2) Front O2 sensor went bad
3) Rear O2 sensor went bad
4) Cat went bad

I was looking at cats on Advance Auto's website and I saw the following 3 cats that fit her car:

Walker Cat #1 - P/N - 15844
Walker Cat#2 - P/N 15063
Walker Cat #3 - P/N - 15051

What are the differences btwn the 3 cats?

Also, question for MechMike, - of the 4 possibilities which is the most likely culprit and which is the least likely? The only thing around here that has changed lately is that it is much hotter (outside temp) than it has been the last time my gf drove her car. She mainly takes mass trans and leaves her car parked for a week or two at a time.

Thanks in advance for any insight or help provided!

mechmike0034

What DTC (diagnostic trouble code) caused the CEL to come on? Did you pull codes using a scan tool? How do you know that it is one of those four issues?

OBD II DTCs and their diagnostic routines are very specific.

How many miles on the car?

Be careful using an aftermarket or "universal fit" cat in a state which has emissions inspection. Many aftermarket cats do not have the oxygen storage capacity necessary for proper operation.

A catalyst DTC (P0420) can take months to set if the vehicle is infrequently driven.

Page 7 of this .pdf gives a simple overview of how the Toyota OBD II cat monitor works...

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guiseppewv

Sorry I thought I posted that code in my OP but I didn't. grrrr

P0420 was the code. I did pull the codes using a scan tool. I then looked it up on the internet to find out what it meant.

About 110k on the car.

Is there an aftermarket cat that you recommend? What is the difference btwn those three that I posted? I just want to know for my own edification.

Daedalus

The Advanced Auto site is down right now, but I think you can rule out front O2 sensor. It's probably either the rear sensor or the cat. Cats have excellent longevity barring external issues (fuel leak, using the wrong fuel, physical damage, etc). My money is on the O2 sensor, which is relatively cheap and easy to fix.

BUT before you spend a dime are you certain the car is no longer covered under some kind of emission warranty?

guiseppewv

Good thought. I did not even think of checking. Once I checked, I found out that the fed warranty is 8 yrs or 80k mi which are both long passed.

mechmike0034

O2 range, switch frequency, and time-to-activity have their own diagnostic routines and DTCs.

If there is no exhaust leak in the vicinity of the cat then the problem is the cat itself.

Again, the PCM's diagnostic routines to determine failure are pretty specific. They have to be. If the PCM errs, the vehicle doesn't maintain emissions compliance, and the USEPA doesn't like that. Passing a system that fails is bad, and so is failing a system that actually is in compliance.

mechmike0034

Were there any other codes set? I have done a little more research and discovered that Toyota's system is a little different. This uses a wide-range air-fuel ratio sensor in place of the normal upstream oxygen sensor. An oxygen sensor is used downstream (post-cat).

I don't know the difference in the specific converters. I am going to consult with some colleagues who are more Toyota-centric and see what I can find out.

Edit - is this car burning oil? This seems to be an issue on that generation of Corolla. This can "poison" the cat.

guiseppewv

No other codes were set.

I don't think the car is burning oil, however, I am not in/around the car enough to have noticed. I will check on that.

Thank you for checking into this for me. You are always a super huge help on cars and car related stuff!

mechmike0034

Pull the 15 amp fuse labeled EFI or F-HTR out of the junction block/fusebox on the left side of the engine compartment. Leave it out for a few minutes. This'll clear the code, turn the CEL off and reset all the adaptives. It may run a little funny right after you do this until the PCM relearns idle and fuel trims.

If the vehicle sees mostly short trips, get it out on the highway for 30-45 minutes - enough to get the cat good and hot. See if the DTC returns. Maybe the cat isn't getting hot enough to burn off any contaminants. This is probably a long shot, but it is worth a try. Include several full-throttle accelerations to heat the cat up.

A P0420 won't hurt anything, and won't cause any "collateral damage", but it will keep the vehicle from passing emissions inspection.

More when I find out more...

guiseppewv

Thanks!

I got the code reset on Sat and used the gf's car this weekend to drive around. Took a few shorter (~15-20 min) trips and 3 longer (30-45 min trips). I did not do any full-throttle accelerations, however, I am 100% sure the car was at least at operating temp. The light has not come back on.

Thank you for all the help. I know the problem isn't entirely gone, yet, however, it is good that the code is not coming back on.

BTW - the car does not look to be burning oil.

mechmike0034

If the cat is just over the fail threshold it may take some time to come back on.

Stay tuned...

mechmike0034

Here's what one source said:


You don't have much of a way to monitor fuel trim readings (these are data parameters which indicate the amount of short and long term adjustment the ECM is making to its internally-programmed fuel delivery strategy...) but the rest of the advise given echoes my suggestions.

Fuel trim works like this:

If there's a vacuum leak, for example, less air would flow through the airflow meter at a given engine speed because unmetered air is entering the engine via the vacuum leak. The PCM would attempt to compensate for this by decreasing the amount of fuel injected as a result.

If there were a leaking fuel injector, fuel pressure regulator, or canister purge solenoid, the engine would run rich, and the The PCM would attempt to compensate for this (after "seeing" this richer-than-normal mixture via the A/F or Oxygen sensor) by decreasing the amount of fuel injected.

An exhaust leak can cause air to be drawn into the exhaust system during periods of negative exhaust pressure. If the A/F or oxygen sensor (mounted in the exhaust manifold) "sees" this extra oxygen, the PCM compensates by increasing the amount of fuel injected.

Thus endeth the lesson for today...

How soon will you need to get this thing through an emissions test?

guiseppewv

Thank you for the lesson!


I need to ask the gf about the next scheduled emissions testing. I think she just had it done in April or March, so it probably isn't due for another couple years. Now that my gf knows what the cat does, she will not put off fixing it if the light comes back on and stays on. She is extremely environmentally conscious (I really like this about her) and would not want to drive around with a faulty cat.