Catalytic converter questions

Chuckman

Chuckman

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My wife's Honda Odyssey and my son's Honda CRV just threw a couple CC 'check engine' codes, but both are running just fine. Awfully coincidental, both within a week of each other. Can the weather affect this? That's the only variable that has really changed. Trying to take care of the low-hanging fruit before I decide whether to spend a couple grand on a 9 year old minivan and 12 year old CRV.
 
How old are your batteries and has the cars sat for a few days?
 
Get them someplace where the codes can be checked (Autozone, etc.). Could be a simple as a loose/bad gas cap. Until then you're just guessing.

Some times the codes are 'general' and only the stealer has the tools to decipher further.
 
Free scan somewhere to see ahat codes are thrown. Then go home and research causes and simple fixes. I highly doubt its the cat as the original honda ones go forever. Hopefully its an easy fix.
 
Our '06 Odyssey has thrown the cat code for about 8 years. The van has 3 cats on it and it does not specify which one might be bad. Years ago when we checked with our mechanic, it was going to be about $1800 to replace them, and I'm sure it is a lot more now. We ignore the code unless it is near time for inspection, then we clear the codes, drive it around to build up history and then get it inspected. The van is not worth spending the money on it to fix it as it is primarily only used as a dog hauler now.
 
Take all the O2 sensors out and clean them. If that doesn’t work after a complete OBD2 reset then replace them. Cheap start on repair and sensors do get dirty. Some O2 sensors are cheap, some run up to $150.
 
amnesia said:
How old are your batteries and has the cars sat for a few days?
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Batts are under 4 years each, we've been driving them on the regular (i.e., every day).

rdinatal said:
Get them someplace where the codes can be checked (Autozone, etc.). Could be a simple as a loose/bad gas cap. Until then you're just guessing.

Some times the codes are 'general' and only the stealer has the tools to decipher further.
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Yep, codes P0174, P0171, P0128, P0430 per Auto Zone.

beamernc said:
Our '06 Odyssey has thrown the cat code for about 8 years. The van has 3 cats on it and it does not specify which one might be bad. Years ago when we checked with our mechanic, it was going to be about $1800 to replace them, and I'm sure it is a lot more now. We ignore the code unless it is near time for inspection, then we clear the codes, drive it around to build up history and then get it inspected. The van is not worth spending the money on it to fix it as it is primarily only used as a dog hauler now.
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That's a good idea.
 
BlackGun said:
Take all the O2 sensors out and clean them. If that doesn’t work after a complete OBD2 reset then replace them. Cheap start on repair and sensors do get dirty. Some O2 sensors are cheap, some run up to $150.
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Good God, I would not even know how to go about find them much less cleaning them.

The climax of my auto repair knowledge is using a Chilton's to change out a water pump and carb on a 1976 AMC Gremlin.
 
What mileage on the vehicles? 80K is often a magic number for when they start taking a dump.
 
Do you know what an "Italian tune-up" is?

Get the car up to operating temperature. Then go drive the piss out of it for a few minutes. Mat the pedal and keep it there for two or three gears.

It can work wonders for cars that are babied a little too much. A cloud of carbon comes out the exhaust pipe and the car is happy again 🙂
 
C-doodle said:
Do you know what an "Italian tune-up" is?

Get the car up to operating temperature. Then go drive the piss out of it for a few minutes. Mat the pedal and keep it there for two or three gears.

It can work wonders for cars that are babied a little too much. A cloud of carbon comes out the exhaust pipe and the car is happy again 🙂
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Or, it just goes fun'goo. 🤌
 
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I’m a smog tech. If you have other codes it’s best to repair them first. However cat effiency codes are rarely false codes. To set a p0420 or 430 the processor has to see switching activity in the post cat o2 sensor. A bad o2 usually fails to function or switch and remains steady. So a bad o2 does not ‘switch’ properly and hence does not set cat efficiency codes. With the exception of some new recent modern tech cars the pcm is looking at the post catalyst o2 sensor for activity because a properly functioning catalyst will have a steady o2 sensor reading due to the chemical reaction in the cat. I’ll post a pic to demonstrate
 
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The top is a switching pre cat o2, the bottom is post cat o2. If they look the same after the cat it is flagged with a p0420,430 low efficiency dtc. I hope that helps to save you trouble. Its addressed with a new cat 99.99999 percent of the time
 
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Buuuuut, the cats gotta be hot. And that p0128 is insuff coolant temp and usually a thermostat. Fix that, clear dtc. And If cat effiency codes return. It needs a cat
 
JoeAz said:
Buuuuut, the cats gotta be hot. And that p0128 is insuff coolant temp and usually a thermostat. Fix that, clear dtc. And If cat effiency codes return. It needs a cat
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So the cat codes could be downstream effect of the thermostat? A new thermostat could clear that?
 
Chuckman said:
So the cat codes could be downstream effect of the thermostat? A new thermostat could clear that?
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Yes.

Cat problems could also be triggered by intake gasket issues (MPG decrease) or head gasket (cats and O2 sensors don't like burnt oil or coolant).
 
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Chuckman said:
Good God, I would not even know how to go about find them much less cleaning them.

The climax of my auto repair knowledge is using a Chilton's to change out a water pump and carb on a 1976 AMC Gremlin.
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They are in the exhaust system, usually easy access on a set of home ramps. The last sensor I replaced was $22 fix. But it was not an OEM part so itmay not last long.
 
Schattenreiter said:
Did you check to see if someone has tried to liberate them????
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Ever had it happen to you? That's a pretty easy check, start the vehicle. We had the converters cut off my wifes Sequoia down in Hilton Head a few years ago at a restaurant. There were 4 or 5 other vehicles that got hit at the same time. Drove back to Charlotte with basically open headers in the 5.7. Memorable experience.
 
Carolinatlc said:
Ever had it happen to you? That's a pretty easy check, start the vehicle. We had the converters cut off my wifes Sequoia down in Hilton Head a few years ago at a restaurant. There were 4 or 5 other vehicles that got hit at the same time. Drove back to Charlotte with basically open headers in the 5.7. Memorable experience.
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I was thinking more along the lines of someone getting interrupted just after getting started than them actually getting it off. I was diesel and DEF system trained and I know that exhaust leaks can cause all sorts of codes.
 
Chuckman said:
Yep, codes P0174, P0171, P0128, P0430 per Auto Zone.
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If I had 2 vehicles that threw cat codes at the same time I'd be suspicious of contaminated fuel. However, you've got other problems that you need to look at first before I condemned the cat. P0128 means the vehicle isn't warming up. That needs to be fixed. It is probably running cold and has a weak thermostat. The P0171/P0174 mean that it's running lean, and the fuel trims are having to add fuel to keep the fuel mixture in bounds. If the fuel mixture isn't correct, the cats can't work. The whole thing might be fixed with a thermostat. A good tech will be able to tell you by taking a little time to diagnose it.
If you haven't heard, emission inspections are going away in all NC counties except Mecklenburg, so you'll be safe to drive it with just a P0420, but you need to get those other codes fixed regardless of the inspection laws.
Joe
 
Chuckman said:
Good God, I would not even know how to go about find them much less cleaning them.

The climax of my auto repair knowledge is using a Chilton's to change out a water pump and carb on a 1976 AMC Gremlin.
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Check YouTube. It should not be difficult. Might be a pain to get to them. But they are mounted on the exhaust system fore and aft of the cats.
 
JoeR said:
If I had 2 vehicles that threw cat codes at the same time I'd be suspicious of contaminated fuel. However, you've got other problems that you need to look at first before I condemned the cat. P0128 means the vehicle isn't warming up. That needs to be fixed. It is probably running cold and has a weak thermostat. The P0171/P0174 mean that it's running lean, and the fuel trims are having to add fuel to keep the fuel mixture in bounds. If the fuel mixture isn't correct, the cats can't work. The whole thing might be fixed with a thermostat. A good tech will be able to tell you by taking a little time to diagnose it.
If you haven't heard, emission inspections are going away in all NC counties except Mecklenburg, so you'll be safe to drive it with just a P0420, but you need to get those other codes fixed regardless of the inspection laws.
Joe
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I was an auto tech for 20 years. All of the above is correct. With the engine not warming up all the way, the PCM will add fuel. You're also getting the lean codes, which typically points to a vacuum leak or more unlikely a weak mass airflow sensor.
I will add that I have seen multiple times on Japanese cars that a very small exhaust leak upstream of the converters can create a venturi effect and draw air into the exhaust system causing the 420/430 codes.

I'd start with the thermostat, check that there's not some vacuum line unhooked, clear codes and go from there.
 
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chiefjason said:
Check YouTube. It should not be difficult. Might be a pain to get to them. But they are mounted on the exhaust system fore and aft of the cats.
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At one time I thought I would have to change mine, but the fault ended up being a dying battery. Even though the car was starting and running fine, it threw a ton of exhaust system codes that led me to think it might be the O2 sensors. Those bastards are seized as tight in there as it's possible to be seized, I ended up giving up before I got even the first one out. At least they were expensive too.

Check your batteries OP, it could be a lot easier than sensors.
 
Talked with my wife, next week we'll get the thermostat replaced and go from there. It'll fix the issues and we'll be good to go, or there will be more repairs to be had and we'll have a discussion about another vehicle.
 
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