2003 I4MT5 Coupe Gets Dreaded P0420 - Drive Accord Honda Forums | radio-pro.ru
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post #1 of 20 Old 01-11-2018, 04:25 PM Thread Starter
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2003 I4MT5 Coupe Gets Dreaded P0420

With all the computer power these days, OBDII just flashes a CEL to annoy everyone and worry them about continued driving the car and potential expensive repairs. Why not flash up the DTC with a bit of information. Service department profits are a higher priority that informed drivers I guess!!

So it's a P0420 cat converter below threshold.

The old Coupe has 260 Mm and is hardly new so I shoudn't complain.

But a few questions.

Been -20 C degrees here for 3 weeks and I did short slow trips on icy roads during this timeframe. So no chance for "youthful" driving to warm up the cat. So the cat might have never gotten efficient and so a DTC thrown.

Does this "cold cat theory" make sense?

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post #2 of 20 Old 01-11-2018, 05:10 PM
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Originally Posted by WDHewson View Post
With all the computer power these days, OBDII just flashes a CEL to annoy everyone and worry them about continued driving the car and potential expensive repairs. Why not flash up the DTC with a bit of information. Service department profits are a higher priority that informed drivers I guess!!

So it's a P0420 cat converter below threshold.

The old Coupe has 260 Mm and is hardly new so I shoudn't complain.

But a few questions.

Been -20 C degrees here for 3 weeks and I did short slow trips on icy roads during this timeframe. So no chance for "youthful" driving to warm up the cat. So the cat might have never gotten efficient and so a DTC thrown.

Does this "cold cat theory" make sense?
Makes some sense, Mine did that during a very cold spell when only highway driving. I expected that the Cat never reached operating temperature with all the frigid air blowing around at 60mph. Went on for a week and never came on again.
If you are burning more oil than a quart in 2000 miles though, the cat may have seen better days.


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post #3 of 20 Old 01-11-2018, 06:11 PM
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New O2 sensors bro.

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post #4 of 20 Old 01-11-2018, 06:16 PM
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Quote:
Originally Posted by WDHewson View Post
With all the computer power these days, OBDII just flashes a CEL to annoy everyone and worry them about continued driving the car and potential expensive repairs. Why not flash up the DTC with a bit of information. Service department profits are a higher priority that informed drivers I guess!!

So it's a P0420 cat converter below threshold.
Okay, I was gonna say if your CEL is flashing then it is having an active misfire, and to stop whatever you are doing immediately.


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post #5 of 20 Old 01-11-2018, 08:40 PM
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Originally Posted by WDHewson View Post
With all the computer power these days, OBDII just flashes a CEL to annoy everyone and worry them about continued driving the car and potential expensive repairs. Why not flash up the DTC with a bit of information. Service department profits are a higher priority that informed drivers I guess!!

So it's a P0420 cat converter below threshold.

The old Coupe has 260 Mm and is hardly new so I shoudn't complain.

But a few questions.

Been -20 C degrees here for 3 weeks and I did short slow trips on icy roads during this timeframe. So no chance for "youthful" driving to warm up the cat. So the cat might have never gotten efficient and so a DTC thrown.

Does this "cold cat theory" make sense?
2007 i4 / 5mt here.
I had the same CEL on starting last Friday. This was in -20 to -25 celcius, likely the same weather as you. Same short trips were made, so i may have triggered the code.
I took the car in a couple days ago. Both up/downstream o2 sensors were apparently fine, but like you said 'cat.converter efficiency below threshold' P0420 code.
Therefore, assessed as faulty cat. converter. Recommended replacement. There was something else wrong with the converter, but I don't recall what.
Replaced with aftermarket AP direct fit 642189. Road test = cat. temp came up quickly.

This has likely been the coldest weather since I've owned the car in the past 5 years.
That's also the 2nd most expensive repair I've experienced with this car yet, after front ball joints/upper control arms.

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post #6 of 20 Old 01-12-2018, 06:11 AM Thread Starter
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Thanks for the input guys.

My oil consumption is about 1 liter in 7500km, so I'm hoping not to have the cat overly poisoned by ash.

No flashing CEL was thrown

If the HO2 sensors are bad they could mis-evaluate the cat, but I'm hoping the programming is sophisticated enough to throw an HO2 code before they throw a wrong code for the cat.

As an update.........I battery disconnected to clear the P0420, and did 4 trips yesterday without the code coming back. Weather was above 0 C. I want to do a few fast kilometers to get the cat lit for several minutes.

Naturally and perversely my CEL based emissions test for Ontario is due in March 2018.

I'll update this thread soon.
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post #7 of 20 Old 01-12-2018, 06:57 AM
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Does this "cold cat theory" make sense?
Just slightly. If memory serves me well, the CEL would trigger if the upstream and downstream O2 sensors record a temp difference outside an allowable range. Since the sensors are both immersed in the same cold weather, it shouldn't make a difference. So to state the obvious, you either have a weak sensor or a failing CAT. At least, that's my theory anyway. Go with the cheapest option first. Maybe jimijam can jump on the Google and give you his expert opinion.

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post #8 of 20 Old 01-12-2018, 03:12 PM
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I had to Google "HO2 sensor" and "260 Mm" just to figure out what the hell is going on here. Must be important, but who knows.

I did learn that burning 1 liter oil per 7500 km translates to 1.05669 quarts per 4660.284 miles. Seems to be an average amount of oil burning other i4 owners here are experiencing.

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post #9 of 20 Old 01-12-2018, 08:59 PM
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Burning a quart of oil every 4500 miles won't kill a cat. My I4 has burned a quart of oil approx every 2500 miles over the last 60,000 miles, cat still good.

Another car I have that used to burn a quart every 500 miles over the course of 20,000 miles (now fixed) and the cat is still good.

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post #10 of 20 Old 01-12-2018, 09:33 PM
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Burning a quart of oil every 4500 miles won't kill a cat. My I4 has burned a quart of oil approx every 2500 miles over the last 60,000 miles, cat still good.
Have you been using that oil recommended by Drew03Accord, or the stuff chris918 recommends?

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post #11 of 20 Old 01-13-2018, 07:32 PM
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Have you been using that oil recommended by Drew03Accord, or the stuff chris918 recommends?
No on the Drew03's QSUD, not sure what Chris918 uses. The oil burning started while I still had my cars under the care of a local indy mechanic. Dealing with this is partially how I became my own mechanic.

I would say the oil most often used during this period when I changed it myself was Castrol 0W-40 Euro, as I was trying to use the higher viscosity to reduce the burn rate. When the oil burning rate increased to 900 miles a quart, I did the seafoam cylinder soak, and since then it is much improved.

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post #12 of 20 Old 01-13-2018, 08:16 PM
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Originally Posted by WDHewson View Post
With all the computer power these days, OBDII just flashes a CEL to annoy everyone and worry them about continued driving the car and potential expensive repairs. Why not flash up the DTC with a bit of information. Service department profits are a higher priority that informed drivers I guess!!

So it's a P0420 cat converter below threshold.

The old Coupe has 260 Mm and is hardly new so I shoudn't complain.

But a few questions.

Been -20 C degrees here for 3 weeks and I did short slow trips on icy roads during this timeframe. So no chance for "youthful" driving to warm up the cat. So the cat might have never gotten efficient and so a DTC thrown.

Does this "cold cat theory" make sense?
Yes, our 7th gen has the code and CEL from November to May every year since 2014. It started at about 100k miles. Car it at 154k now. Seems to coincide with when the car began to burn oil. This past summer, we solved the oil burning issue. The CEL and code came back even so, but much later ( made it well into December this time). But last week was the coldest week here in the east that we've had in years and at present, the CEL is off. This is the first January since 2014 that the CEL is off.

My son now drives this car, but I do monitor it. One of the last times I drove it I did some testing as follows: I did a 50 mile trip on the highway on a cold winter day and brought my scan tool. I reset the CEL. About 6-8 miles into the trip, the CEL and code came back. I reset it. At about the same interval, the code and CEL came back again. I reset it and the CEL stayed off the remainder of the trip.

In fact I can say with almost certainty, that every time the CEL has come on, It has always been during the first 10-15 minutes of a trip. If I made it past that point, it wouldn't happen during that particular trip

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post #13 of 20 Old 01-14-2018, 02:41 PM Thread Starter
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Yes, our 7th gen has the code and CEL from November to May every year since 2014. It started at about 100k miles. Car it at 154k now. Seems to coincide with when the car began to burn oil. This past summer, we solved the oil burning issue. The CEL and code came back even so, but much later ( made it well into December this time). But last week was the coldest week here in the east that we've had in years and at present, the CEL is off. This is the first January since 2014 that the CEL is off.

My son now drives this car, but I do monitor it. One of the last times I drove it I did some testing as follows: I did a 50 mile trip on the highway on a cold winter day and brought my scan tool. I reset the CEL. About 6-8 miles into the trip, the CEL and code came back. I reset it. At about the same interval, the code and CEL came back again. I reset it and the CEL stayed off the remainder of the trip.

In fact I can say with almost certainty, that every time the CEL has come on, It has always been during the first 10-15 minutes of a trip. If I made it past that point, it wouldn't happen during that particular trip
Thanks BenzAccord. I've been trying to figure out if my cat was too cold to be effective. It looks like all three reactions that are catalyzed have a similar temperature dependence. I'm not sure which of the reactions the HO2 sensors are monitoring. Maybe all three.

I think it's possible in the very cold spell that I had a "cool cat" and conversion was low. Especially since my cat's heat shield is significantly rotted away and did not keep the heat in.

I've gone 4 days without the P0420 recurring and temperatures around here are about -5 C. If the code isn't thrown again I'll go for the emissions test later this week.
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post #14 of 20 Old 01-14-2018, 04:06 PM
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Thanks BenzAccord. I've been trying to figure out if my cat was too cold to be effective. It looks like all three reactions that are catalyzed have a similar temperature dependence. I'm not sure which of the reactions the HO2 sensors are monitoring. Maybe all three.

I think it's possible in the very cold spell that I had a "cool cat" and conversion was low. Especially since my cat's heat shield is significantly rotted away and did not keep the heat in.

I've gone 4 days without the P0420 recurring and temperatures around here are about -5 C. If the code isn't thrown again I'll go for the emissions test later this week.
In my state: NJ, all they do is read the codes. I took this car for emissions inspection, the same day that the CEL cleared itself, and they passed me. Good luck!

There are some technical service bulletins out there for our car's that are strictly a software update to address this issue. My belief is that the software update probably delays the test from running thereby allowing the temp to rise. I'm not 100% sure though.

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post #15 of 20 Old 01-15-2018, 04:34 PM Thread Starter
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Thanks BenzAccord.

I cleared the P0420 with a battery disconnect, so I might need quite a few drive cycles for the system to pass for Ontario's code reading. Although I really have no idea of how Honda's OBDII software really works.

Appreciate the tip about TSBs on the problem. I'll search around to see if I can find them

If the CEL stays unlighted by Thursday, I'll go for the emissions test with fingers crossed

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