Another P0420 Code, 98 Obw

[blaze]

YUP, been tagged with the P0420 DTC

Found a small leak downstream at the Mid pipe flange with the Muffler section, no leaks upstream of the Cats.

My CanOBD2 Code Reader pulled the following data:

 

Report#: 1

Report Date: 1-17-2008 (5:47 PM)

Vehicle Year: 1998

Vehicle Make: Subaru

Vehicle Model: LEGACY, OUTBACK

Vehicle Engine Size: 2.5

Vehicle VIN:

Vehicle License Plate:

Vehicle Mileage:

 

Stored:

P0420 Catalyst System Efficiency Below Threshold (Bank 1)

 

Pending:

P0420 Catalyst System Efficiency Below Threshold (Bank 1)

 

MIL ON

MisFire Monitor Complete

Fuel System Monitor Complete

Comprehensive Component Monitor Complete

Catalyst Monitor Complete

Heated Catalyst Monitor Not Supported

Evaporative System Monitor Complete

Secondary Air System Monitor Not Supported

A/C System Refrigerant Monitor Not Supported

Oxygen Sensor Monitor Complete

Oxygen Sensor Heater Monitor Complete

EGR System Monitor Complete

 

DTC for which Freeze Frame was Stored P0420

Fuel System 1 Status Closed Loop

Fuel System 2 Status Not Supported

Calculated LOAD Value 14.51 %

Engine Coolant Temp 183.20 °F

Short Term Fuel Trim - Bank 1 1.56 %

Long Term Fuel Trim - Bank 1 4.69 %

Intake Manifold Absolute Pressure 12.99 inHg

Engine RPM 2275 rpm

Vehicle Speed Sensor 49.71 mph

[nipper]

Now turn your head and cough....

 

 

Fix the exhaust leak.

 

Your car is old enough to need a front O2 sensor from subaru.

 

What is the mileage anyway?

 

nipper

[blaze]

What is the mileage anyway?

 

nipper

 

200,000 miles, I plan on getting a new o2 sensor 1st

[nipper]

200,000 miles, I plan on getting a new o2 sensor 1st

 

Ah so its just broken in

 

 

nipper

[blaze]

Ah so its just broken in

 

 

nipper

 

Looks and feels like it just came out of the showroom :-p

[Bmm001]

Or, you could try resetting the CEL and see if it comes back on. If it stays off, don't worry about it. Mine comes on every few months and I just reset it and forget about it until the next time it comes back on.

 

Brian

[blaze]

Or, you could try resetting the CEL and see if it comes back on. If it stays off, don't worry about it. Mine comes on every few months and I just reset it and forget about it until the next time it comes back on.

 

Brian

 

Already tried that, thanks for the help.

 

I'm thinking the same as Nipper, time to replace the o2 sensor.

[OB99W]

[...]I'm thinking the same as Nipper, time to replace the o2 sensor.

The first thing to do is fix exhaust leaks; if any are near the rear O2 sensor, that can cause a false indication of cat inefficiency without affecting other operation.

 

It may be time to replace the front sensor, but there's a chance in your case it won't affect the P0420, or at least not for long. The freeze frame data you posted indicates the LTFT at under 5%, and positive; that means the ECU thinks the mixture was somewhat lean, and is slightly enriching to compensate. That relatively small amount of compensation usually doesn't point to a particularly bad front O2 sensor; in fact, it could be explained by a small intake leak. (Ideally both STFT and LTFT should be near 0%, but indicating a few percent is typical.)

 

At 200k miles, the cat itself may be the culprit. However, assuming that the O2 sensors haven't been changed in all those miles, replacement would be good anyway; the front one will help protect a new cat, if it turns out it's needed.

[blaze]

It may be time to replace the front sensor, but there's a chance in your case it won't affect the P0420, or at least not for long. The freeze frame data you posted indicates the LTFT at under 5%, and positive; that means the ECU thinks the mixture was somewhat lean, and is slightly enriching to compensate. That relatively small amount of compensation usually doesn't point to a particularly bad front O2 sensor; in fact, it could be explained by a small intake leak. (Ideally both STFT and LTFT should be near 0%, but indicating a few percent is typical.)

 

Thanks, I'll look into that possible intake leak

[2X2KOB]

Wow, that's a lot of info. What kind of code reader are you using?

 

Somewhat related, Harbor Freight has a CAN capable code reader for $40.

 

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=94169

 

This cheapie won't give you THAT kind of information, though.

[blaze]

Wow, that's a lot of info. What kind of code reader are you using?

 

Somewhat related, Harbor Freight has a CAN capable code reader for $40.

 

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=94169

 

This cheapie won't give you THAT kind of information, though.

 

Its a INNOVA 3100a , Web site http://www.CanOBD2.com. There are all types and models at there web site.

You can buy this one now for 129.00 bucks at Sears, or WalMart for 98 bucks here in Maine. Cheapest one at this Walmart is just a INNOVA reader for around 60 bucks (less bells and whistles than the 3100a). The 3100a comes with a USB cable and software to link it up to your computer and down load info ,as you see in my original post.

 

INNOVA 3100a - Its a plug and play, 15 sec conn, all in one display, definitions (don't need to look up code), Freeze Frame, Internet upgradable, Erase code, Auto link, Memory, PC-Link, Shop Report, 11 Emission Monitors .

[OB99W]

Thanks, I'll look into that possible intake leak

Just to be clear, although it's worth taking a look, that isn't going to resolve the P0420. My point was that changing the oxygen sensor might not either, and you may still need a cat in the long run. Cars that set P0420 and benefit most from a new O2 sensor typically don't have 200k miles on the cat, and often show the sensor as troublesome by a high percentage LTFT.

[blaze]

Just to be clear, although it's worth taking a look, that isn't going to resolve the P0420. My point was that changing the oxygen sensor might not either, and you may still need a cat in the long run. Cars that set P0420 and benefit most from a new O2 sensor typically don't have 200k miles on the cat, and often show the sensor as troublesome by a high percentage LTFT.

 

 

Thanks again, I don't know how many miles are on the cat? It came with the OBW when I bought it USED. Far as I know it has 200,000 miles?

I do know all the heat shields have been removed, and the exhuast parts have Subaru stamped on them. I'm looking at replacing the exhuast system with OEM soon, along with o2 sensors.

[nipper]

Blu got the same code at 205,000 miles. replaced the O2 sensor, and the code is gone. Original cat at 220,000 miles.

 

Replace the O2 sensor, worst thats going to happen is that you have a bad cat, the code will still be there, (then we replace the rear one too) and youve saved much dollars. If the cat is still bad, you would have had to replace the sensors anyway, so no loss.

 

 

nipper

[blaze]

Blu got the same code at 205,000 miles. replaced the O2 sensor, and the code is gone. Original cat at 220,000 miles.

 

Replace the O2 sensor, worst thats going to happen is that you have a bad cat, the code will still be there, (then we replace the rear one too) and youve saved much dollars. If the cat is still bad, you would have had to replace the sensors anyway, so no loss.

 

 

nipper

 

Thats exactly the way I plan to replace the system. Front o2, then 2nd O2, then the cats. Thanks

[OB99W]

Thats exactly the way I plan to replace the system. Front o2, then 2nd O2, then the cats. Thanks

Since you've got a scanner, would you mind posting the fuel trims and other relevant data after the front O2 sensor is replaced and has been run a few weeks? It would be a useful reference to compare with current readings.

[WoodsWagon]

Replacing the whole system with OEM parts will make you cry at the parts counter. You're looking at 1800-2000 in parts. Not counting labor.

 

My dad's legacy had the 420 at 150k miles. We replaced the front and rear 02 sensors with the Bosch universals ($60 apice) and it's been fixed for a while now.

[2X2KOB]

Thanks for the details on your code reader.

 

Here is an alternate solution that works, if one is short on cash.