Can 'Limp Home Mode' Happen at Home?

Dear Car Talk

Dear Car Talk | Dec 21, 2017

Dear Car Talk:

I have a 2008 Saturn Outlook with around 88,000 miles on it. Right after starting it in the driveway, it began making a weird noise, and a warning came on the dashboard that said "Reduced Engine Power." When pushing the accelerator, the rpm wouldn't increase. I let the car sit for a little bit, started it again, and it ran fine. This is the second time it's happened. What's going on? -- Mary

Thanks, Mary. You've actually answered a question that's troubled philosophers for years: If your '08 Saturn had reduced engine power, how would you know? Now we know that the answer is "the dashboard light comes on."

Your car went into something called "Limp Home Mode." It's the same mode you go into when you bang your knee on the neighbor's piano bench during a dinner party.

Actually, Limp Home Mode is there to protect the catalytic converter -- especially when it's under warranty. If something goes wrong that has the potential to damage the converter, especially at high engine speed (like a condition where too much unburned gasoline is getting into the exhaust stream and could overheat the converter), the computer will engage Limp Home Mode, which limits the car to very low rpm but allows you to what? Limp home -- if you're not far from home.

Why did it happen? It can happen for a number of reasons. But the fact that it temporarily fixed itself with a restart suggests to me that one of your sensors is out of whack. So you can expect this problem to recur. It may start happening more frequently. And, at some point, a restart won't fix it.

So limp over to your mechanic and have him scan it. He'll plug his scan tool into the car's computer port and read the code that the computer will have stored from this last incident. That'll tell him whether it's a cam sensor, for instance, a crank sensor or something else. Good luck, Mary.

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