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Discussion Starter #1
02 OB pulling the '0420'

'Sup peeps. My wife and I now have 'his and hers' Outbacks - hers is an '01 with 206k, mine a just-bought '02 with 156k. Dig 'em both :29:

The new 02 had the CE light from day one. During the test drive we took it to AutoZone, pulled codes, discovered the 0420. Took it to our local dealership, they racked it, confirmed the 0420 code, and gave us the usual story of 'bad cats', as well as a 'running rich' condition, and needs a new air filter.

We have noticed that under the same general driving conditions (around town) the fuel economy of the '02 is about 2-3 mpg less than our '01. That would jibe with the running rich. It runs fine - no stalling or misfiring that we can detect, but mileage does seem to be a bit 'low'.

Reading the threads (good info in here btw), looks like the 0420 code indicates 'catalytic converters' but does not necessarily mean they're bad - could likely be the O2 sensor(s)...but no distinct insight as to which one - front or rear...and maybe there isn't any real way to discover if either are bad, and if so which one(s)?

I have also read about replacing the PCV and clearing fault codes, but have not got smart on how to clear codes (yet). Did I read right that disconnecting the neg batt cable clears the code(s)?

Will likely replace air filter, plugs, and wires asaply (pulled misfire codes on the 01 recently).

Would appreciate clear insight as to what order of sequence to troubleshoot? PCV?, O2 sensor(s)?, then cats?, then...?

Yer thoughts are much appreciated :)

- Sam
 

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Look up my post on "Diag P0420"

The dealer saw what the issue was, but was trying to get you to bite as you are unschooled in engine performance. He told you it was running rich? Rich will cause a 420. The misfire is a dead giveaway also.

Start with plugs, cables, new fuel filter, clean the throttle body and air filter if you need it. Pour a full 12 oz bottle of Sea Foam in a full tank of gas, disconnect the battery negative terminal for a minute and reattach, tightly, then drive it. Within 25 miles the emission monitors will set with exception of the EVAP. If not, you can run by your AutoZone and have them check the codes again, looking at "pending" and see what monitors are not set and post it here.

From there, if necessary, you can check the rest of the engine systems.

Always follow the list I posted in Diag P0420. The CAT is always the least likely culprit. You always check to see whats happening in front of the CAT first.

.
 

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Discussion Starter #5
- wanted to post up on the results of some maintenance. I replaced the plugs and wires, fuel and air filters, cleaned out the PCV - it was really gunked up, and ran a bottle of seafoam.

The plugs looked aweful - like they had been blowing compression past the porcelain shafts for a while. Wires didn't look much better. No appreciable oil in the tunnels tho.

The CEL reset itself during the process, and remained off for a few days, then reappeared with the same 420 code as before. However, fuel mileage came up by 2-3 mpg, and that was all kinds of 'happy'!

Few days later I had to make a trip to the airport - about a 1.5 hr drive. After the flight, get back in the car, start, and the CEL did not come back on. :29:

Drove home 1.5 hrs, CEL remained off. Few days later, came back on. :28: Fuel mileage remaines at 26-27 mpg average.. :29:

Car continues to run good. Starting to suspect the front O2 sensor.

Additional thoughts?

- Sam
 

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1. make sure you don't have any exhaust leaks.
2. replace the front and rear O2 sensors
3. do the $5 fix, spark and be done with it.
(Double check thread size - should be standard, but here's an example:
O2 Extender Oxygen Sensor Spacer HHO Test Pipe 1 | eBay)

I personally skip #2, the 0420 debacle is not worth my time. type P0420 in google and see how much of a run around it is if you need convincing.

Highly unlikely your converters have failed, I can't stress how robust those converters are. If you haven't had some catastrophic engine issue they're fine. Most Subaru's from the 80's still have their original converters in lands where rust isn't an issue.
 

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Discussion Starter #7
well I'll try a $5 fix just for good measure. The #3 - that's the Dorman pn# 42009? Is that for the upstream or down stream sensor...or both?
 

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well I'll try a $5 fix just for good measure. The #3 - that's the Dorman pn# 42009? Is that for the upstream or down stream sensor...or both?
i just buy multi-packs off ebay now but the ones in the auto parts stores you used to have to drill the inside out for clearance for the O2 sensor...so if you don't mind drilling sure get that.

or if you want it ready to go order one off ebay already ready to go.
 

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well I'll try a $5 fix just for good measure. The #3 - that's the Dorman pn# 42009? Is that for the upstream or down stream sensor...or both?
You may need a thermostat. Given the time frame in the driving, and the time between on/off, I think your thermostat is sticking. If it sticks open on a long drive, the engine experiences what's referred to as heat sink. The temperature in the radiator matches the temp of the engine due to constant flow. New stat and flush it.

If you can borrow or get a scan tool that reads live data, you could watch the temperature to verify it.

Keep in mind that if it occasionally sticks open, it can also stick closed causing a overtemp condition.
 

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Mine is on/off about 2 days each. The temp gauge seems to always be a hair under 1/2. It's been this way since the day I bought it in November.

I'm slowly starting to tackle this. New rear O2 before I bought it. When the light was on for that, the VDC OFF light was on with it. That hasn't been an issue since.
 

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Mine is on/off about 2 days each. The temp gauge seems to always be a hair under 1/2. It's been this way since the day I bought it in November.

I'm slowly starting to tackle this. New rear O2 before I bought it. When the light was on for that, the VDC OFF light was on with it. That hasn't been an issue since.
The VDC Off will illuminate when there is a performance issue with he Engine or Trans since the program uses both to control the car. The service you've completed probably corrected that part.

I would still suggest a thermostat replacement and flush. Especially since you don't know when it was done last. Use a Subaru stat. Comes with the seal. About $25 plus the coolant and its easy to get to. 2 bolts.

And, it's easier than the $5 fix. :29:
 

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Discussion Starter #12
saw a video on youtube where a guy does the $5 fix, but he used two of the fittings and screwed one into the other, then the O2. As I understand tho, this fix just requires a single adaptor (drilled out) correct?

- Sam
 

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I was being sarcastic. The "$5 fix" is not a fix. It's a mask to the ECM and does nothing towards repairing the fault.

Owners who don't know how the system functions or ones that give up trying to locate the problem themselves will attempt this "patch". Some manufacturers utilize the rear O2 to assist with fuel trims, Nissan for example on some models, and removing the O2 from the direct air flow inhibits proper trim calculation.

The rear O2 will tell you a lot when you know how to read the data in comparison to the other output sensors and needs to remain functional.
 

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Discussion Starter #14
OIC - well I don't want to do a band-aid fix; I thought maybe the O2 sensor extension made the system perform better and/or clear the fault. Well...back to the drawing board. Thx
 

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The spacer basically acts as a way to move the sensor partially out of the O2 stream and lower the voltage that is being detected off the sensor and clears the PO420. You can try it and see if that clears the error.

Id recommend changing the O2 sensors (front is "Air/Fuel Sensor") before doing anything drastic. I ended up doing everything with the end result that I had a massive crack in my front cat, with the substrate gone.
 
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