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Discussion Starter · #1 ·
It seems that all the O2 sensor discussions I can find on the forums are for older models or 2.5l engines. I have a 2011 Outback 3.6R with ~ 160k miles on it. The CEL, traction control, cruise control, and brake warning lights all come on together at random intervals. Sometimes it can go for weeks without the lights, sometimes they come on every time I start it up.

We have an independent shop we've been using for nearly 20 years and have a lot of trust in them. They have told me they pull oxygen sensor codes and say that these symptoms are consistent with the oxygen sensors going bad. They've quoted me $600+ to replace them. I've crawled under the car and find four of them, 3 easy to reach, one pretty tough. If I do this myself I want to make sure I know what I am doing, and why the shop I trust is quoting $600 for what looks like a relatively easy job.

Has anyone else replaced the O2 sensors on a 4th gen 3.6R engine? Can you tell me what's involved, and does anyone have a diagram showing their locations? I already own an O2 sensor wrench from work on other vehicles.
Thanks!
 

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01 VDC, 05 R Sedan, 06 BAJA EJ257
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One, I'd like to know what the codes are. It would be odd for the ECM to set codes for all 4 at the same time.

Second, the sensors for this car are not cheap. OEM part numbers are for the front, 22641AA53A, and for the rear 22690AA68A. Subaru list is $192.45 front, and $149.95 rear; each. Labor calls for 1.5 front and 1.7 rear, but if all 4 were quoted it should have been just 2 hours total. The labor time posted is if you are just doing the front or just doing the rear, not all 4, so the times shouldn't be added together to get the 3.2 hrs.

Rock Auto has the sensors for $100 and $60 each. Plus shipping.

They also have the gaskets; VICTOR REINZ 111069101 for $16.12/pair and the rear gasket, a WALKER 31630 for $10.62.

As for a diagram, here it is.
501351


The two rear sensors on top of the cat tend to be a bugger to loosen up, so if it comes to replacing them be sure to spray them down with PB Blaster or the like and let it sit for 5-10 minutes and make sure you use a wrench that fits snug so you don't strip the sensor. Otherwise you'll be dropping the pipes. Which may be a good way to go anyway if you change all four just because the rear sensors may give you an issue and having the pipes on the ground will ease the situation a bit. You can get manifold gaskets and the rear pipe gasket fairly inexpensive.

NOW, on the issue. Someone needs to check the ampere output of the battery and conductance through the battery cables end to end, specifically the ground cable. Then all the grounds on the engine need to be checked for breakage and corrosion. Once all the grounds are repaired, then you go to the sensors and test them.

Testing is done with a multimeter and you test from the sensor connector, not the harness side.

FRONT
501352


REAR
501353


If the sensor(s) test bad, then the proper thing to do is to watch the datastream for how the sensors are acting in comparison to other data points dealing with MAP, Temps and combustion. A vacuum leak will make the AF and O2 sensors act up. Poor gas will do the same and the fuel trim corrections will show it.
 

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Discussion Starter · #3 ·
Hey Cardoc,

Thanks for your very thorough reply! I don't know which codes they were pulling. I had a Bluedriver OBDII reader, but it seems to have died because it won't connect anymore and flashes a red light instead of blue.

I don't think it was showing all 4 sensors were bad, they were recommending all of them at the same time just to cover all the bases I think - it has been a while since I had it in to the shop - just been living with the occasional dash lights, but I know the cruise control and traction control don't work when those lights are on, so it's time to get this resolved.

I will call my shop and talk through this with them again and see if they went through the ampere output of the battery and conductance through the battery cables and the ground cable and grounds before checking the sensors.

Are the gaskets you mentioned for the oxygen sensors, or the pipes?

Looks like ~ $320 or so for parts, plus tax and shipping. I need to decide if it's worth trying to save $300 vs. how much time and headache it will take me. Thanks a million for your help!
 

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The gaskets I posted are for the pipes should you drop them out of the car. Which I recommend based on experiences with the rear sensors.
 

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Discussion Starter · #5 ·
Cardoc,
When you recommended,
check the ampere output of the battery and conductance through the battery cables end to end, specifically the ground cable. Then all the grounds on the engine need to be checked for breakage and corrosion.
Is this in response to the dash lights, or throwing O2 sensor codes?
thanks!
 

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The codes and operation of the systems as a whole.

The dash lights up because there is a problem with drivetrain management. The cruise and traction systems can't work properly with an engine or trans management issue. The engine, trans and ABS/VDC systems work in conjunction and a problem with one effects the others.

If your mechanic has a Midtronics tester he should know how to use it for the battery and cable checks. If he doesn't, he hasn't gotten that far in learning about how electrical conductance effects everything.

I'd be willing to bet that if all the modules were scanned there will be communication codes on most of them and lack of communication leads to poor electrical systems.

You could very well have a bad sensor. The electrical still needs to be checked just based on the age and mileage to get ahead of any other issues and get everything running at par.
 

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Discussion Starter · #7 ·
Hey Cardoc, that makes good sense. I'm a physicist by training so I have an understanding of the effects of conductance, grounds, etc. I will include your recommendations in my discussion with my mechanic next week. Thanks very much!
 

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Discussion Starter · #8 ·
I decided to try some DIY troubleshooting based on your statements about conductance and grounds. Meanwhile I was able to get my Bluedriver OBD2 scanner working. This morning I was fortunate enough to have the car lighting up the CEL, brake, cruise, and traction control lights while I had the Bluedriver connected. It read out the following codes:
P0333: knock/combustion vibration sensor 2 circuit high bank 2 (both current and permanent readings)
U0110: lost communication with drive motor control module 'A'
C1040: no description available
C10CA: no description available
B1101: no description available
B1102: no description available
U1201: no description available

Cardoc, can you speculate on what is going on based on these codes?
thanks!
 

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Battery and/or grounds together.

DTC B1101 BATT P/SUPPLY MALFUNCTION CONT

DTC B1102 BATT P/SUPPLY MALFUNCTION BACKUP

U1201 CAN-HS COUNTER ABNORMAL

All C codes are communication issues and leads to current flow.

The knock sensor may be bad, especially if you have a salty environment. Bank 2 can be replaced by removing the alternator. Bank 1 the AC compressor off will give you some space. You'd have to test the sensor. Approx 560 ohms between the two terminals. Spec also allows +/- 28.
 

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OK

having done this job myself for the rear o2

1. all 4 sensors are easily accessible from under the car. there is literally nothing in the way.
2. the 2 rear sensor are even easier to access with the front wheels off the car

but I am not sure you have o2 senor problems as the codes you pulled are U (network) B (Body Integration Unit) and C (communications codes)

P333 is as you described a knock sensor code. to get to that sensor (driver side) requires removal of the alternator and if you want it to be easy, the A/C pump. It is next to impossible to test that sensor in the car due to how the connector is orientated

as for the codes
 

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Discussion Starter · #11 ·
Starting with the simplest things first; is diagnosing the battery as simple as measuring the DC voltage, or does it require an AC conductance test? I just measured the voltage at 12.3V - car sitting in garage overnight. Did not disconnect battery cables to measure voltage. The battery was new from Walmart last June. I also have a battery load tester, which shows the battery is ok - 675 CCA. I have a battery minder charger connected now. It went from bulk charge to float in about 5 minutes, which seems kind of odd considering the 12.3V starting point.

I know how to test the battery cable conductance - look at voltage drop when starting vehicle. Are there ways for me to check engine grounds, or does this require a professional level diagnostic system?

thanks!
 

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You check cable conductance with an ohm meter. From the negative post to the lground lug by the starter should be 0.0 ohm.
 

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Discussion Starter · #13 ·
I have read that automotive quality ohmmeters do not have the required sensitivity to directly measure the very small resistance differences in battery cables that make a difference in performance.
 

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If you are using an ammeter that checks ampere flow between the post with the car off, all you do is leave the positive clamp on the battery and move the negative clamp to the ground lug by the starter. Take your initial measure and subtract the measue at the lug and that's your loss. Anything over 75 amps is bad.
 

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Discussion Starter · #15 ·
I don't follow - not sure what you meant where typo 'schecjs' shows up. Pretty sure the ammeter function of my multimeter won't handle that kind of amperage.
 
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