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Discussion Starter #1 (Edited)
Hello Subaru Forums! First time posting here after the recent updates so I may leave things out unintentionally so please let me know. I have a question I have a 2013 Outback with 144,298 miles on it. Just had it serviced at the dealer for a P0351 where they replaced plugs and ignition coil wire. The dealer is now saying that the main electrical harness may be bad and should be replaced because after time resistance builds up in it and it could cause those codes.
Does that make sense? and should this be the next troubleshooting step. The cost for the part is around $250 and labor is around $450 for an estimated total of around $675-700.
 

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@13SubaruOutbackNA I'm in the same boat, for the code, the flowchart ends at the problem being a plug or the coil. Then button up and see if it goes away.... After that, it sounds like guess work (the tech I spoke with says this too). Might be the main harness or it could be the ECU.

If the harness were bad, it would be/should be seen in steps 1, 2, or 3 of the flowchart. I get the code incredibly randomly, I have a hard time believing it is the wiring. In my case I'd believe more something sporadic with the ECU.

Before I shell out $$$$$$$ for parts (in Canada here, I did price a wiring harness: $1,451.74!! for that alone. Dunno about ECU), I'm going through all the grounds, connectors, running a can of fuel additive and using supreme gas for a while. A bad ground may cause ipthe issue, no harm in cleaning injectors with better fuels/seafoam too. Been a bit busy lately and put off checking it out, it's been good for the past while now.
 

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It is fairly uncommon (but not unheard of) for a Subaru ECU to have problems and I would discount that as the cause of the problem straight away unless everything else proves to not be the problem.

Having done just a little research on the P0351 code I would suspect the main cause of this code in a properly maintained vehicle (a vehicle which has had all maintenance done as scheduled and is using Tier One fuel) would be a poor electrical connection to the "coil on plug" unit or a faulty "coil on plug" unit.

If your spark plugs are more than 60,000 miles old this would be the first thing I would replace. Replace with NGK plugs as used/recommended by Subaru. It may also be worthwhile adding some Seafoam or Techron to the next two tanks of fuel, especially if you have not been using "tier one fuel"

Replacing the spark plugs will re-seat the electrical connector to the "coil on plug" unit (as you need to remove and replace the connector when you replace the spark plugs).

If this does not solve the problem I would then be inspecting the major wiring harness connectors to ensure all pins are connecting OK. This is becoming one of the developing problems in vehicles due to the many electrical signals/connections that allow communication to the ECU and BIU modules. A bad electrical connection can lead to a DTC code as others have advised elsewhere on this forum.

Good luck with your troubleshooting, this type of fault often needs lots of time and patience to sort through to find the "real problem".

Seagrass
 

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Good luck with your troubleshooting, this type of fault often needs lots of time and patience to sort through to find the "real problem".
I agree. Probably why it is just easier to replace the wiring harness. Honestly, if my option to buy the harness was 250, I would just get it and know (maybe hope) it is ok.

I just took apart the main connector and it seemed wet or oily. I cleaned it out and am now testing this. Hope it was that simple! I'm getting 0.1 ohms to the coil connectors and the ECU. I'd say the wiring is ok....
 

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I had the same problem a while back with my subaru legacy. Problem turned out to be I needed my valve cover casket replaced. One of the gaskets that seals the spark plug was leaking oil and fouling the plug. Mine occurred with 260,000 miles.
Now on the P2096 problem you could replace the O2 sensors(both) but make sure you use subaru o2 sensors. There is a software issue that causes this problem in certain cases(not really sure what cases those are) but i talked to a subaru mechanic that told me there needs to be a software fix to correct the issue but Subaru national will not do it because it would not be cost effective(guess not enough cars have the issue). Mechanic says he sees the problem increase when refineries switch over to winter gas blends.
 

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Update: Thanks for all the great advice. I did have the work done by the dealer and so far the P0351 code has gone away. Like suggested it probably was easier just to let them replace the harness and insure all the connectors/connections were good.

The P2096 code is still on but now the dealer wants to replace the catalytic converters and sensors ($1,800+). One thing I left out was that the short block was recently replaced on this car due to oil burning. I am not sure if that could have damaged the converters. I recently had the sensors replaced with Subaru sensors about 20,000 miles back due it's oil burning days. The car is in great shape and running good, it just has the P2096 code. Is it possible to just replace the back converter (I think it is the cheaper of the two)? I was hoping to replace it with a Walker aftermarket part from Rock Auto or somewhere like that. Or I thinking to drive with the code for a bit since I know that more or less all the ignition parts have been replaced.
 

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@13SubaruOutbackNA I'm in the same boat, for the code, the flowchart ends at the problem being a plug or the coil. Then button up and see if it goes away.... After that, it sounds like guess work (the tech I spoke with says this too). Might be the main harness or it could be the ECU.

If the harness were bad, it would be/should be seen in steps 1, 2, or 3 of the flowchart. I get the code incredibly randomly, I have a hard time believing it is the wiring. In my case I'd believe more something sporadic with the ECU.

Before I shell out $$$$$$$ for parts (in Canada here, I did price a wiring harness: $1,451.74!! for that alone. Dunno about ECU), I'm going through all the grounds, connectors, running a can of fuel additive and using supreme gas for a while. A bad ground may cause ipthe issue, no harm in cleaning injectors with better fuels/seafoam too. Been a bit busy lately and put off checking it out, it's been good for the past while now.
Wow yes I agree.
 

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I agree. Probably why it is just easier to replace the wiring harness. Honestly, if my option to buy the harness was 250, I would just get it and know (maybe hope) it is ok.

I just took apart the main connector and it seemed wet or oily. I cleaned it out and am now testing this. Hope it was that simple! I'm getting 0.1 ohms to the coil connectors and the ECU. I'd say the wiring is ok....
Thanks. The dealer replaced it and the P0351 code seems to be gone so far.
 
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