Broken coil on 2015 Impreza - replace all four or just one?

[Tisorp]

I have a 2015 Subaru Impreza coupe.  The car has about 75,000 miles on it.  While driving home from work about a week ago, the car suddenly began driving very rough with the check engine light coming on in a flashing mode within 3-4 minutes.  I proceeded to drive directly to the local Subaru dealership, which was only a 5-10 minute drive away.

 

Upon performing a diagnosis, they informed me that one of the coils was bad.  As there are four coils, it raised the question of whether I should replace all four coils or just the one.  Here's what I learned from the dealership:

 

• Subaru recommends replacing only the bad coil should one go bad
• If a bumper to bumper warranty (or other warranty covering the coil) were in place and a coil went bad, Subaru would only replace the single coil
• The dealership indicated that just because one coil went bad doesn't mean the other coils are any more likely to go bad than if they were on a different car which had similar mileage but never had a coil go bad
• There is no recommended mileage at which the coils should be replaced
• Coils cannot be measured for wear and tear.  E.g. it's a black & white thing - either it works or it doesn't work.
• The dealer says the only real reason to replace all four would be for peace of mind
• My driving habits or the service history had nothing to do with the coil going bad 

Based on this info, there doesn't seem to be any reason to waste the money to get all four replaced.  Is there any reason I should get all four replaced as opposed to just the one?

 

Thanks in advance for all feedback

Edited March 14, 2018 by Tisorp

[GeneralDisorder]

Failure is rare. Replace only the bad coil.

 

GD

[idosubaru]

Exactly. Replace 1, they very typically last the life of the vehicle.

 

Replacing all 4 for no reason is almost comical.

 

The old adage of replacing parts in sets is overplayed.

[kamesama980]

3rd vote for just one.

 

there are things to replace in sets so they wear symmetrically or because of the effort involved: you don't replace one ring on one piston. you shouldn't replace one tire in a 4wd and many full time AWD cars.

 

Coils do wear out, the magnetic properties of the core change over time but the lifespan/degradation time of on ignition coil is so long and there's enough overhead before you'd notice that it's meaningless to the lifespan of the car as a whole. It's not even a consideration with the mean-time-before-failure calculation.

[keith3267]

Just one and use OEM.  If you replace with aftermarket coils that are not OEM suppliers, it would be possible to have them fail before any of the remaining coils go.

 

BTW, coils can be measured for wear and tear, but the test is really expensive and only done on large industrial distribution transformers, i.e. substation transformers.

Edited March 14, 2018 by keith3267