A Persistent Check Engine Light Baffles Mechanics

Dear Car Talk

Dear Car Talk | Sep 26, 2017

Dear Car Talk:

I have a 2006 Volvo V70 wagon with 119,000 miles. For the past two years, the check engine light has been on, and the car's message panel says the engine system needs attention. I've taken the car to three reputable mechanics, including a Volvo dealer, and no one seems to be able to find a problem. The car runs fine, and I've been told that as long as it continues to drive well, I shouldn't sweat it.

But the possibility of an issue continues to hang over my head. Should I be concerned? I have a second car -- a 2011 Subaru Impreza -- that I use more regularly because I'm worried I'm going to be stranded someday with the Volvo. -- Janine



Well, Janine, if the Volvo dealer couldn't sell you any repairs, how am I supposed to have any shot at it?

It's odd that the car's computer hasn't stored a code. Normally, when the check engine light comes on, the computer will store data that -- when read by the mechanic's scan tool -- will tell him which component reported the problem and what needs to be tested.

The possible good news for you is that usually when the check engine light comes on, it's not something that's going to leave you stranded.

Of course, there are plenty of other things on a 10-year-old Volvo that can leave you stranded, so I don't want to give you a false sense of confidence here.

But the components that turn on the check engine light usually are related to the emissions system. It could be a fuel-air ratio sensor, a problem with the vapor recovery system in the fuel tank, or -- with 120,000 miles on the car -- a catalytic converter that's ready to be replaced.

Unfortunately, it also could come on if the transmission isn't shifting properly. That's the one that could leave you stranded.

The problem also could be the computer itself. And if your dealer is really indebted to you (if you've paid off several of his boats over the years with your Volvo repair bills), maybe he'll swap in another computer for you as a test, and let you drive the car and see if the light goes off.

That's what I'd recommend. Since you're afraid to drive the car, you have to start somewhere. So test the computer first.

If it's not the computer, and the transmission is not noticeably misbehaving, my advice would be to keep driving for now ... until you either get someone to read a stored code, you fail your emissions inspection or your transmission bites the dust. Good luck, Janine.


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