P0420 Diag

[cardoc]

I had another Subie in today with a 420 code. Ended up being the fuel pump. Too weak to supply sufficient fuel and pressure. It was 12 psi short when I tested it. Fuel filter was good. He also had a long stretch of cheap gas. I forewarned him that he may be looking at a replacement CAT later on. Maybe not. I advised him to change his fuel brand and run premium through the winter months to help compensate for winter blends and we aren't cold enough.

I took a video of the scan tool data but I inadvertently deleted it from the phone. But to give you a run down, LTFT was at 11.7, the rear O2 was high indicating rich. The plugs were the wrong ones, so I went ahead and replaced them with platinum NGK. In the end, fuel trim dropped to 2, rear O2 dropped to avg between .55 and .65. I was also reminded why I opted out of owning a Forester. You can't just tilt the seat up to get to the harness, and too much to remove from the rear to get to the fuel pump. But it all worked out good.

[plain OM]

cardoc:

Any experience with the 2005+ and perhaps other later models?

There doesn't appear to be a specifically-identified "STFT" and "LTFT". (See attached list from 07 FSM).

I believe the relevant PIDs are "AF Correction #1" and "AF Learning #1" respectively but would appreciate your comment, especially as this might be useful for others using this thread as a P0420 troubleshooting guide with a later model that might not read out the STFT and LTFT.

Also note that there's also "AF Correction #3" and AF Learning #3" which, like the other two, will show up with those descriptions in scanner readouts but are not otherwise identified as to their significance.

(Incidentally, all of these PIDs show up when scanning my 07 engine PIDs with Romraider Logger, however "Intake Manifold Absolute Pressure" is identified as "Boost". It took me a while to make this connection . . .)

[contrail_25]

Cardoc, need some of your wisdom on gas and the P0420 code. Reference the original P0420 problem I had here.

Since fixing the o-ring on the IAT/MAP sensor I have not gotten the P0113 code, but I have gotten the P0420 a couple times now.

When I was in Germany all fuel had 5% ethanol and if I remember correctly I was using 95 (RON)...so probably around 90-91 in US standards (AKI). I never got the P0420 code in the three years I drove over there. First day back in the states, first tank of gas, I get the code. I've been using mid-grade here in NC. I've gotten the code within 50-60 miles of each refuel the past few weeks. The last refuel, I put in premium, no code yet.

Ideas?

[cardoc]

Originally Posted by plain OM

cardoc:

Any experience with the 2005+ and perhaps other later models?

There doesn't appear to be a specifically-identified "STFT" and "LTFT". (See attached list from 07 FSM).

I believe the relevant PIDs are "AF Correction #1" and "AF Learning #1" respectively but would appreciate your comment, especially as this might be useful for others using this thread as a P0420 troubleshooting guide with a later model that might not read out the STFT and LTFT.

Also note that there's also "AF Correction #3" and AF Learning #3" which, like the other two, will show up with those descriptions in scanner readouts but are not otherwise identified as to their significance.

(Incidentally, all of these PIDs show up when scanning my 07 engine PIDs with Romraider Logger, however "Intake Manifold Absolute Pressure" is identified as "Boost". It took me a while to make this connection . . .)

For some reason, your attachment isn't opening. I'll look into that later.

RomRaider is a tricky software package. The definitions for the ECMs are generalized for use with multiple types of ECMs and TCMs.

The Denso ECM begins a learning curve for fuel trim every time its started. It does this due to changes in temperature, pressure, etc.. Once it learns the new fuel trim data necessary, it stores it and uses that value for all closed loop operation.

The AF values are calculated in Lamda, EQRatio 1/1, 2/1, 3/1 depending on H4, H6, NZEV or PZEV vehicles, but you can change the value in RomRaider to show AF at stoichiometric if it makes reading the data easier.

The AF correction and AF learning are the values utilized by the ECM to calculate closed loop trims. The LTFT and STFT can be calculated based on the Learning and Correction respectively. You just have to watch it while you log and do the math. Or graph it and watch the waveform. Once the computer realizes there has been a change in data input, it goes back to the correction and learning to compensate. Its when there is an issue with performance and the computer is making a lot of correction in its learning curve that the MIL comes on. It sees an issue with the LTFT learning, or that input data is out of range and sets the code for the system it believes is the issue.

Now, to effectively diagnose the issue with a P0420 using aftermarket software and determine where the problem lies, and we will use RomRaider since it is widely used by Subaru owners for various reasons, log the data from the rear O2 sensor. In RomRaider, click the Rear O2 Sensor and use either Amps or Volts. When graphing this sensor, the activity of the sensor is the same as any other scan tool and the value will remain steady rich or lean indicating a fuel or ignition issue, or it will fluctuate rich/lean based on the AF Learning value

You don't necessarily need the AF values to determine if a CAT is bad. All you need to remember is the O2 sensor reports the Oxygen content of the exhaust exiting the CAT. Anytime you see a wave instead of a steady value, the CAT is bad. Otherwise, with a 420 code, you are looking to see if the O2 is rich or lean, then start with locating the issue with engine performance following with sensor outputs.

As far as the RomRaider component title in the log lists, as long as you know what you are recording, all is good. As long as you understand what values are necessary for proper performance.

My VDC actually reports Lamda values, but I can alter the RomRaider to show Stoich. I also have different scan tools that show different values. The EVO will show Stoich or Lambda depending on which value I choose to look at, either AF or EQ.

I will record a video of my car and post it if I get time today. I will use both the EVO and RomRaider. You'll just have to remember I am running E85 and have 2 6.2L cats installed so the O2 sensor values will be scewed. I just get hot air out the tailpipe.

[cardoc]

Originally Posted by contrail_25

Cardoc, need some of your wisdom on gas and the P0420 code. Reference the original P0420 problem I had here.

Since fixing the o-ring on the IAT/MAP sensor I have not gotten the P0113 code, but I have gotten the P0420 a couple times now.

When I was in Germany all fuel had 5% ethanol and if I remember correctly I was using 95 (RON)...so probably around 90-91 in US standards (AKI). I never got the P0420 code in the three years I drove over there. First day back in the states, first tank of gas, I get the code. I've been using mid-grade here in NC. I've gotten the code within 50-60 miles of each refuel the past few weeks. The last refuel, I put in premium, no code yet.

Ideas?

The brand of gasoline sometimes does make a difference in P0420 issues. Murphy gasolines (Wal Mart) and certain grocer stations purchase what is referred to as "shelf" blends. I have customers that have helped me out with experimentation with gasolines by running a tier 1 gas in the car then switch to the cheap stuff. After filling with the cheaper gas, the MIL would come on for 420. We would leave it alone through the tank of fuel and they would refill with the tier 1 gas and after driving, the light would go off.

My VDC does it now. I run E85, no MIL. I go back to Premium and the light will come on for too rich. Leave it, go back to E85, and the light goes out after 10 miles driving. This car is programmed for boost and fuel and it doesn't like gasoline any longer. The last few reflashes we did to the ROM was on E85, so the injector cycle makes it run rich with gas.

Low quality fuel does not burn well and the high HC in the exhaust reduces the oxygen which causes either a rich code or 420.

[cardoc]

2001 Subaru Outback VDC Scanner Readouts - YouTube

2001 Subaru Outback VDC Scanner Readouts - YouTube

[plain OM]

cardoc:

Once again, thanks for the detailed answer/explanation in post #24, and the video. It's a real lesson for me, and hopefully will help others.

I will look back at Romraider Logger to see if I can switch out of the Lamda indication -- I hadn't noticed that, but didn't pay attention because this is the readout term the FSM indicates.

But it's your explanation of the relationships that's going to be most useful. And as programs such as Romraider Logger, and FreeSSM, are easily available, and need only a connecting cable, readers should be much better able to deal with the P0420. (For others not familiar with FreeSSM and Romraider Logger, see: FreeSSM - Complete access to your ECM and TCU)

Edit: Re second para. above, cardoc is correct; I checked and Romraider can be changed to read sensor detail rather than Lamda.

[Chonman111]

got the classic p0420 code... I believe this is under a recall from suburu does anybody know?

[plain OM]

There is a "recall" for reprogramming of the engine control module software. This is supposed to help avoid future failure of the catalytic converter. Part of the reprogramming procedure involves tests to see if the catalytic converter is already failing, in which case it would be replaced, otherwise the software is just updated. However, as this thread demonstrates, a P0420 does not necessarily mean the converter is faulty -- the code can be caused by something totally different, such as the thermostat.

[cardoc]

Originally Posted by plain OM

There is a "recall" for reprogramming of the engine control module software. This is supposed to help avoid future failure of the catalytic converter. Part of the reprogramming procedure involves tests to see if the catalytic converter is already failing, in which case it would be replaced, otherwise the software is just updated. However, as this thread demonstrates, a P0420 does not necessarily mean the converter is faulty -- the code can be caused by something totally different, such as the thermostat.

And, when you take it in to the dealer, if they find something other than what is outlined in the recall that will correct the efficiency of the CAT, if its not warranted, you pay.

How many miles? Filters good? Fuel cheap or good brand?