Dear Tom and Ray:
I have a 2006 Dodge Durango with 118,000 miles. Recently, the turn signals have developed a mind of their own. I turn on the left turn signal, and after faking me out by blinking left, it will, of its own accord, start blinking right, even though the signal handle stays in the left turn position. It does not do this all the time, but it's getting more frequent. Of course, it does not do this when I take it to my mechanic, who says he has to see it to fix it. The hazard lights do the same. After initially working as designed, they will go haywire, like shorted-out Christmas lights, and blink any which way. — Dennis
Ray: Well, that sounds festive, Dennis.
Tom: I'm glad there's something to cheer you up, because we're not going to make you happy.
Ray: Unfortunately, while most cars use a $25 flasher module to control the directional and hazard lights, this particular model uses a microcomputer under the fuse box called a front control module.
Tom: Why is that bad news? The Dodge dealer gets about $700 for one of these puppies.
Ray: If you have a dealer who is kind-hearted, sweet-natured and susceptible to the smell of warm brownies (which you'll arrive carrying), you can try to get him to work with you. Ask him if he'd be willing to install a new FCM as a test to see if that solves the problem.
Tom: It simply plugs in, so installation is not a big deal. If it fixes the problem, everyone's happy. Well, except you, since you're out $700. But at least you've fixed your truck.
Ray: But if the FCM doesn't fix it, a willing dealer can simply swap your old one back in and you guys can try another solution.
Tom: With electronic parts like these, there's no harm in testing one in a car and, if it doesn't solve the problem, putting it back on the shelf for another customer. The part still will function as new.
Ray: Less likely to be causing the problem but just as easy to test is the body control module, another microcomputer involved in all kinds of lighting, plus door locks, electric windows and ventilation functions.
Tom: But if your dealer won't work with you to test the modules, that makes things a lot harder. Without more evidence, I, personally, wouldn't start by buying replacement modules. They're a lot of money. And if you spend $700 on a black box and it turns out your old black box was perfectly fine, you'd understandably be bent out of shape.
Ray: So I think if I had to lay out my own money to try something, I'd probably try the multifunction switch first.
Tom: The multifunction switch is the stalk on the left side of the steering column that you push up and down to engage your turn signals. Unlike the computerized modules, the switch has moving parts, which we know wear out over time.
Ray: A new one will cost you about $300, installed. The dealership where we get our Dodge parts sells quite a few of them, so perhaps that's what's causing the problem.
Tom: And by the way, part sales histories can help you make better-educated guesses about stuff like this. If you ask your dealer's parts guy if they sell a lot of BCMs for this car and he says they never sell them, that's a clue that they generally don't go bad, and that's probably not your issue.
Ray: If he says they sell 15 a week, you may be onto something. We wish you the best of luck, Dennis! And while you're working on it, use your hand signals.
(Car Talk is a nationally syndicated column by automotive experts (and brothers) Tom and Ray Magliozzi. Write to them at the Car Talk website.)