Subaru Outback Forums banner

2041 - 2060 of 2145 Posts

·
Registered
Joined
·
17,450 Posts
@cardoc @jvandyke

I guess I took myself down a rabbit hole . . . .

Several times in the past I raised questions about the absence of any A/F Sensor trouble codes, given that all the criteria for detecting the related faults seemed to be met. Now, I think the answer was there all along.

An example is the P0030, which relates directly to the Sensor Resistance. As the logs show, the resistance is remaining high for an inordinate time after engine start, yet there's no code. I've always had an idea that this was a clue.

https://www.subaruoutback.org/attachments/p0030-criteria-2008-pdf.480689/

For all the related, yet absent, codes, there's one detecting criterion I failed to recognize and that, in fact, is not being satisfied; namely, the sensor heater Control Duty %. It has to be a positive number >0. As the ECM is not turning the heater on and off, the control duty cycle is zero, and so the detecting criteria are not being met. It's the same for the P0032, and P0134.

From the reprogramming recall WVU-31 it appears that the ECM is programmed to turn the heater on under certain conditions, and not turn it on at other times [bold added]:

"This software update is intended to improve vehicle emissions when the vehicle is operated
in cold weather and the engine is turned off and restarted within short periods of time such as
in several minute intervals. The A/F sensor contains a heating element, which is controlled by
the ECM, and which assists the sensor in reaching an optimum temperature, resulting in better
accuracy. When the vehicle is operated under the conditions described above, there could be a
longer than desired delay in the ECM’s turning on the A/F sensor heating element,
resulting in
higher than desired emissions. This software enhancement will correct that condition."

Why would there be a "desired delay" in turning on the heater in the first place? Perhaps, because if the engine and A/F sensor are still quite hot, there might not be a need to turn on the heater when the engine is re-started; the sensor resistance and Closed Loop operation might recover quickly enough on their own. The ECM probably checks these parameters, and only turns the heater on if they don't respond with a pre-determined delay time. The reprogramming might have introduced if, or how, "outside temperature" influences that delay time. It might be that in our present case, that delay is set to some extremely high number, e.g., "infinite". Unfortunately, in our 3rd gens, there isn't an ECM parameter for heater duty cycle, or heater current, and therefore no way to better understand the "delay" under different engine starting conditions. (In the previous generation there is a parameter for Front A/F Sensor Heater Current.)

This brings me back to the ECM firmware. It might well be worthwhile seeking a dealer willing to do a reprogramming of the ECM to ensure it's complete and up-to-date, even if there's a cost. (My invoice for the recall shows 0.6 hrs.) At the least it would get the ECM firmware question out of the way; at best it would correct the heater issue.

Out of the rabbit hole . . .?
 

·
Registered
Joined
·
94 Posts
Excellent. I will pursue this, although it will have to wait until the pandemic is over, we will soon be under lockdown, in about 2 hours they say. Probably won't be venturing across the county for an experiment, although I can call around and ask I suppose.
 

·
Registered
Joined
·
17,450 Posts
Re: the outside temperature relationship, if any, what does the Outside Temperature in the Multi-Information display show? Is it close to the actual temperature? And, after the car has been parked and everything should be at ambient, when Romraider is connected to the ECM are the Coolant Temperature, Oil Temperature, and Intake Temperature all very close to the outside temperature?
 

·
Registered
Joined
·
94 Posts
Re: the outside temperature relationship, if any, what does the Outside Temperature in the Multi-Information display show? Is it close to the actual temperature? And, after the car has been parked and everything should be at ambient, when Romraider is connected to the ECM are the Coolant Temperature, Oil Temperature, and Intake Temperature all very close to the outside temperature?
I will log my next trip. It will be a short one. Stone cold (heated garage 50ish) start. 1/2 mile run, 2 hour shut down, repeat back home. I can take a joyride to get to temperature if that is useful.
 

·
Registered
Joined
·
17,450 Posts
I will log my next trip. It will be a short one. Stone cold (heated garage 50ish) start. 1/2 mile run, 2 hour shut down, repeat back home. I can take a joyride to get to temperature if that is useful.
For my questions, no need to drive. Just ignition at On with the car parked and Romraider connected to the ECM to compare the three engine-related temperatures with the Outside Temp indicated in the dash area. With the car not driven, the temperatures should be similar.

But if you are out and about, what might be interesting is to test the time it takes for the A/F Sensor resistance to drop down and the fuel system to change to CL when the engine and the sensor are already fully warmed up/hot. This is the exact same logging as in the earlier logs, except stop the engine, wait a minute, then start up again with the RR logger started before starting the engine.
 

·
Premium Member
2001 VDC/SC One of a Kind
Joined
·
13,239 Posts
Discussion Starter #2,047
Test mode connectors. When connected, and the ignition is turned to ON (engine not started), the ECM will cycle the radiator fans, a bunch of emissions-related solenoids, and the CEL, on and off. I think it's also used for certain programming functions using the dealer Subaru Select Monitor. Normally left separated.
Yes. The connector is diagnostics. It runs through all the actuators on the car for the tech to check function. It is a necessity in reading the ROM and in conjunction with the white connector close by it which has 2 pins to jump for reflashing. My VDC has 2 toggle switches now. I got tired of up and down the night I re-scaled the 3 BAR MAP to the ROM, so next day, wired them in next to the steering wheel. :cool: Much easier.
 

·
Registered
Joined
·
94 Posts
ambient; 46ish
Multiinfo on dash 46
coolant temp: 46
air intake: 54
oil temp: not being logged
This log was from cold start, didn't do a warm restart one, well I did, but for some reason there's no data in the last two logs I took
 

·
Registered
Joined
·
17,450 Posts
ambient; 46ish
Multiinfo on dash 46
coolant temp: 46
air intake: 54
oil temp: not being logged
This log was from cold start, didn't do a warm restart one, well I did, but for some reason there's no data in the last two logs I took
Air intake temp suggests the engine compartment might not have been cooled down completely after a previous drive, or, perhaps, the effect of full sunshine.
Oil Temp should be an available parameter in RR (it's used by the AVLS system). But, no problem. Ambient and dash temp are good.
Not sure if I will be out with the car any time soon now (our province just announced mandatory shutdown of all non-essential business and activities) but will try the hot start to see how the sensor resistance reacts.

Called Dealer, they want $102 to reflash the ECU, hmmmm
Nothwithstanding our current social distancing , I think I would go for it. Was that dealer involved with the car before?
 

·
Registered
2010 Outback 3.6R 2014 Legacy 2.5i 2003 Legacy L special edition (retired to backup)
Joined
·
918 Posts
well to give an update on my 3.6R

After a new set of plugs and a healthy dose of fuel injector cleaner I have only seen p420 return once in 2K miles. I am thinking the previous owner ran the car with a misfire condition long enough to carbonize the exhaust and cats. I am hoping that now that the engine runs like it was new, this issue is done. Currently at 144600 miles
 

·
Registered
Joined
·
17,450 Posts
@cardoc @jvandyke

Ran three logs today of the A/F Sensor resistance. First was a "cold" start; the car had been parked for several days, and the garage temperature was around 6 C (43 F).

On the first start, it took 20 seconds after the engine start for the resistance to reach 32 Ohms and the fueling to go CL.

The other two were "hot" starts. In both cases, Coolant and Oil temperatures were around 80 C (176 F). In those cases it took between 11 and 13 seconds.

When I was back home I tried scoping the A/F Sensor heater control at pin 4. Because the sensor resistance changes so quickly, there wasn't time to capture the duty cycle waveform on the scope immediately after engine start. However, I was watching the scope while also watching the sensor resistance parameter on my tablet. On engine start, the scope showed the duty cycle signal, with only short pulses of heater "off" time. Seemingly coincident with the resistance drop from 255 to ~30 Ohms, the duty cycle changed and remained fairly steady. Here's the scope display:
481192

The period of the square wave is constant at this point, at about 128 ms or 7.8 cycles per second.
When it's at the low point, the ECM is grounding pin 4, so there's only 0.6 V; when the heater is off, the signal is at battery voltage, in this case, around 14.2 V (engine running).
The "Duty Cycle" is 53%.
From what I could see right after engine start, the "On" time was very high, probably ~95%. There were only momentary spikes visible that would reflect a short "Off" time.
When I did some voltage measurements at pin 4 for an earlier thread some time ago, I noted that the voltage stabilized at around 8 V. According to the scope's measurement table, the "Mean" or "average" is 7.78 V, which is consistent with that earlier voltage measurement.
I hope this provides a bit more understanding of how the heater control works.
 

·
Registered
Joined
·
17,450 Posts
Updating the results of monitoring the heater control.
Today I was able to capture the control signal switching for about a minute, starting with Key On, Engine Off.
At KOEO, the voltage at pin 4 is battery level. As soon as the engine starts, the system voltage goes up to about 14 V. Within 2 seconds, the voltage at Pin 4 drops, but in the first shift, only remains there for a relatively short time. However, this begins the duty cycle function, and within 15 seconds the low V, or heater "on" time, increases to over 95%. Then, by 25 seconds, the duty cycle declined to around 45%, and remained in the 45-48% range to the end of the record.
The decline from 95% duty cycle occurs roughly as the sensor resistance drops to 32 Ohms.
In this case the engine had been started a few times to test out my methodology with the scope so it wasn't warmed up, but wasn't at ambient, when the record was made. The time the duty cycle will remain high (i.e., heater on) will depend on how long it takes for the sensor to heat up and it's resistance to drop.

Here's a clip of the high point: duty cycle almost 98%, as measured by the scope.
481261


And here's the final clip at 48%:
481262


Interesting that the period of the duty cycle is 7.8 Hz. I had thought it would be more of a round number such as 5 or 10, or higher.
I didn't check the rear O2 sensor heater control. Might go back at some point to see if it uses the same rate.
Also, as noted earlier, when the heater is on, the voltage at pin 4 is quite low, in the 0.2 - 0.4 V range. With a 2-3 Ohm heater resistance, and 14 V supply, there's ~5 Amps flowing. That goes through the wiring to the ECM, through the ECM, and to ground via the large bulkhead connectors to the lugs on the intake manifold. That suggests the resistance from heater to ground is less than 0.1 Ohms. Pretty good. When bad grounds are suspected, measuring the low side voltage at pin 4 could be one thing to check. A multimeter with low and high "hold" functions probably could be used instead of a scope.
 

·
Registered
Joined
·
17,450 Posts
I didn't check the rear O2 sensor heater control. Might go back at some point to see if it uses the same rate.
The rear O2 sensor also uses a switching heater control, however, it's a fixed duty cycle, at least on my 07.

Whether from a fully-cold start or a warm start, the switching has a period of about 260 ms (3.8 Hz), with the on time (low voltage) around 52 ms, equivalent to a duty cycle of 20%. (The A/F Sensor heater has a 130 ms period, i.e., 7.8 Hz, with the duty cycle varying from 95% to around 48%.)

Connection was made at pin 1 of the 4-pin rear O2 sensor harness connector E23.

Here's a comparison graph of the A/F Sensor (top) and Rear O2 Sensor heater controls in the first 30 seconds after startup. As noted earlier, the A/F Sensor heater has a high "on" duty cycle but when the sensor resistance drops, the duty cycle goes down to around 48%. This is illustrated by the increased crowding in the upper trace towards the right. In contrast, the Rear O2 Sensor heater control (lower trace) duty cycle remains constant across the graph.
Both heaters comparison.png
And here's a more detailed look at the switching of both sensor heaters after about 50 seconds:
detail.png
 

·
Registered
2003 forester X w/ AT
Joined
·
22 Posts
There are several reasons a P0420 will come up as an error and illuminate the MIL. A lot of people are scared of it. They get all excited and search all over the internet to try and guess at what they should do. Reading good advise and bad trying to save money and hoping its not a Catalytic converter gone bad.

Well, I have been trying to inform as many people as I can that the 420 code is not a scary animal that is going to eat your wallet. This code simply means that somewhere in the chain of events that controls the overall performance of the engine there is a problem and you have to find it.

List of possibilities:

Fuel quality (low quality fuel a/k/a Murphy Gas)
Fuel quantity (filter or pump issue)
ignition issues (plugs, wires, coils injector flow)
temperature control (too high or too low)
vacuum leaks
exhaust leaks (not only an annoying noise, but it effects proper value reporting to the ECM by the AF and O2 sensors)
poor amperage conductivity (i.e. battery or cabling)

Sensor issues can be:

MAF (Mass Air Flow Meter)
MAP (Manifold Absolute Pressure)
ECT (Engine Coolant Temperature)
AF (Air/Fuel ratio a.k.a. Front O2 which can be a single bank 1 for 4 cyl or bank 1 or bank 2 H6)
O2 (This is the actual O2 behind the CAT that lets the computer know how the CAT is functioning)

Very informative! I'm struggling though...have had P0420 for almost a year. I was stupid and replaced the CAT right away along with A/F sensor and 02 sensor. Although after 300k miles I thought it was a good idea. After that, replaced fuel filter in the tank, under the hood, spark plugs, wires, injectors, IAC, coolant temp sensor, no exhaust leaks and replaced any dry or cracking hoses in cases there was a vacuum leak. MAP reads good and my 03 forester X doesn't have a MAF. Coolant temp seems normal on the scanner.
I then started after the EVAP components as a shot in the dark.
Really need some help here. I did notice that the A/F sensor is reading 2.1 v pretty steady. I though those were supposed to read .01 to .9 I'm using a generic actron scanner.
 

·
Premium Member
2001 VDC/SC One of a Kind
Joined
·
13,239 Posts
Discussion Starter #2,056
@Leapdog The AF sensor will give you voltage feedback in the 2V range. Some scan tools will give you Lambda which is around 1, 1 being equal to 14.7:1. Lower than 1 is rich, higher is lean. The rear O2 on the other hand should be around .65-.8V steady if the cat is working. It will drop to 0V when you are driving off throttle and the ECM is cutting fuel. At the same time the AF sensor voltage should go up to 3V range, or, Lambda will be 1.2ish.

In locating an issue, it is good to see what the computer is doing for fueling. You can see this in the STFT (short term fuel trim) and LTFT (long term). STFT is the immediate adjustment the ECM makes to control Lambda fueling based on the AF sensor feedback. If the STFT is +5% or more, it's adding fuel and there is a vacuum leak or fuel delivery issue. If the value is -5% or more, the ECM is reducing fuel due to a lack of complete burn during combustion. This can be bad plugs, poor spark from a coil, a misfire, leaking injector, or it can also be associated with bad feedback from a sensor. In the latter, the ECM thinks the car is running rich when it isn't and it ends up running lean. Usually this is caused by a bad AF sensor, temp sensor, or MAP and IAT and it's calculating the air volume incorrectly as a result.

On electrical flow and supply. Your Forester should have a battery supplying 550 CCA or higher. This has to be measured with an ammeter, I use a Midtronics PBT300, while the battery is cold (sitting at least an hour with the engine off, hood up to dissipate heat) and the engine not running. Some part stores have a meter to test the battery, but best results are with it cold and I don't know anyone that wants to mill around a part store for an hour waiting for the battery to cool. Maybe you could borrow one.

The conductance through the cabling is also important. Just because you have 12.xxV at the battery and ample ampere output does not mean you are getting it to the engine block and body. Even if you have 12.xxV at the battery, this does NOT mean you have ample ampere flow either. I've tested batteries with 12+V and the ampere output will be under 100A. The computers on the car in conjunction with the sensors and outputs (injectors, coil, fuel pump, valve body, along with anything running in the cab like AC which draws a lot of current) will use up a lot of electricity and when the flow is low due to a corroded cable or bad connection at a lug, the electrical devices on the car suffer. Sensors work erratically, the ECM runs slower, like your phone or a laptop with a low battery, the actuators/outputs don't work proper, or fast enough. This is seen most in an automatic where a low battery or bad grounding will cause the clutches in the transmission to burn up due to a lull in solenoid activation due to poor electrical flow. To check the ground and positive cables, you can use the ammeter by moving the negative lead to the end of the ground cable by the starter and test again then compare the drop. If it's 75 or more, the cable or the clamp is bad. With a multi-meter, you want to check the resistance in the cable. That is measured in Ohms. On the main cables between the battery and lugs, battery and engine block, battery and alternator, you want 2 Ohms or less. Between the battery and the body, nor more than 4 Ohms.

As far as the EVAP system is concerned, we have seen one on this forum where the purge valve was stuck open and constantly pulling vapor from the gas tank causing engine performance problems and the P0420. You would have to be able to see the fuel tank pressure with the engine off and then monitor it with the engine running, comparing it to the purge valve operation. If the purge valve is off and there's a vacuum being pulled on the tank, the purge valve is most likely bad.

Rom Raider is your best friend in home diagnostic logging. RomRaider - Open Source ECU Tools | RomRaider / RomRaider

A Vag-COM cable will let you connect the car to the laptop. Any more they are selling as low as $8. You don't need any software with it, just the cable. This one is in California: VAG-COM VCDS USB Cable KKL 409.1 Car Diagnostic Scanner OBD2 Tool for Audi VW | eBay

Logging can be saved in a csv file and uploaded somewhere that can be linked to this forum thread for me, plain OM, or several others to see the data and help lead you to finding the issue.
 

·
Registered
2003 forester X w/ AT
Joined
·
22 Posts
@cardoc Live data at Idle and freeze data when the code triggered. I haven't read your response yet just thought this would be helpful.
IMG_20200408_102425335.jpg
IMG_20200408_102435388.jpg
IMG_20200408_102524836.jpg
IMG_20200408_104051430.jpg
 

·
Registered
2003 forester X w/ AT
Joined
·
22 Posts
@cardoc just read your post. Thanks so much for all the info. Fortunately, I'm trained in electronics so that part will be easy.
"At the same time the AF sensor voltage should go up to 3V range," my A/F goes to 5v when take my foot off the gas to come to a stop.

I'll take the advice and get the cable you mentioned and download the open source software.

Maybe once and for all I can finally nail this down with the help of this thread.
 

·
Premium Member
2001 VDC/SC One of a Kind
Joined
·
13,239 Posts
Discussion Starter #2,059
@Leapdog That's what we're here for.

Freeze frame is useless with this code. The only way to determine what's going on is to see a datastream in 2-5 minute increments.

Cold start
Cruising at about 45-55
Cruising at 65 or higher

Log the following to start with:
AF Sensor
AF Sensor Resistance
RPM
Engine Load
ECT
Battery Voltage
STFT
TPS
IAT
MAP Relative or Absolute, doesn't matter which
Ignition Timing
Knock Correction
Rear O2 Voltage
CPC Duty Cycle (if it's available in the PIDs list on RR)
Fuel Tank Pressure (Same as above)
MPH (just for reference to compare with TPS, Load, etc)
 
2041 - 2060 of 2145 Posts
Top