Ray Magliozzi, Car Talk


Dear Car Talk:


I have a 2011 Subaru Outback.


The "icy road" sensor misreads the road all the time and cuts the power, making the car stutter. It happens most when I turn a corner and slowly accelerate out of the corner.


I got the whole sensor computer box replaced and it stopped happening for four months, but then started again! I hope you can help. — Defne


Let's start by defining a few terms, Defne.


By "icy road" sensor, you mean the traction control system. That uses the car's ABS (anti-lock braking system) to figure out when a wheel is spinning. It brakes just that wheel, and if the wheel keeps spinning, it then reduces engine power to stop it from spinning.


By "whole sensor computer box," we're going to assume you mean the ABS computer.


Now that I've correctly defined your question, I still have no idea what the answer is.


I'll give you two educated guesses, though. The most likely guess is that one of your wheel speed sensors is faulty.


Like the ABS, the traction control system uses the wheel speed sensors to compare how fast each of the four wheels is turning. If one is suddenly turning a lot faster, the "whole sensor computer box" concludes that the wheel must be spinning, and it takes action to stop it from spinning. That should result in your ABS or traction control light coming on. And if a dashboard light is staying on, your car's computer should be able to tell you exactly which sensor is malfunctioning.


If your warning lights have not come on, I suppose you could try testing each sensor with something called a lab scope. Or you could try replacing one wheel speed sensor at a time and seeing if the problem goes away. But that'll cost some money.


A more remote possibility is that it's not the traction control system at all, but a really bad CV joint. The only reason I suggest that is because of when you say the problem occurs. When CV joints go bad, they will often make a clacking noise (not unlike the ABS makes), and it tends to happen when you are accelerating out of a turn. If the CV joint is bad enough, it could even make the car seem like it's losing power.


So, ask your mechanic to check your CV joints, just in case. And if it turns out it was a CV joint all along, ask him if he wants a good deal on a barely used "whole sensor computer box." Good luck, Defne.


Got a question about cars? Write to Ray in care of King Features, 628 Virginia Drive, Orlando, FL 32803, or email by visiting the Car Talk website at cartalk.com.


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