Free scans are a great place to start for diagnostics
Dear Car Talk:The “check engine” light in my 2003 T-Bird came on recently. Several of the local auto parts stores advertise they will run the diagnostics for free and tell you why the light has come on.
The local Ford dealer quoted me $150 to run the diagnostic and tell me what is wrong. Is there a difference between what the auto parts places check and what the dealerships check? — Tim
No. Not on a 2003 car. If you had a 2021 Mercedes, I might recommend you go to the dealer, who would certainly have the latest and greatest diagnostic software and familiarity with the car. But, for a car that’s 20 years old, a scan is a scan. And the scanner they have at the local auto parts place will come up with the same error code that your dealer will, minus the bill for $150.
It could be a sensor has failed, an evaporative emissions problem or a catalytic converter that’s worn out or plugged up.
So, keep in mind that you might need more information than just the results of your scan. You might need to know if it’s something you can fix yourself. You might want to know which evaporative emissions parts typically fail on this generation of Fords. Or, you might wonder what your options are for, say, replacing the converter on an older car.
In that case, you’ll need to go to a mechanic. But, you can save yourself $150 and at least get some preliminary (if not definitive) information about what’s wrong with the free scan. So why not?
Dear Car Talk: I have been the sole owner of a 2001 Lexus 300 ES sedan with 149,000 miles. It has been a great car.
The problem is that the battery dies if I don’t drive the car for two to three days, and then I have to jump-start it. It’s OK if I drive it every day.
The mechanic said the alternator is OK but said that the battery was losing 2 amperes when the car is off, which he said was excessive. The only things that stay on are the clock and the security system. I always check that the lights and radio are not left on overnight.
So, what is making the battery die? Hope you can help.
I am a senior citizen and am not looking to buy a new car. Thanks. — Ellen Well, the good news is that your mechanic has already solved half your problem, Ellen. Now, he just needs to solve the other half. It’s like a doctor who says “you’re bleeding. Good luck with that.”
You say the only things left on overnight are the clock and alarm system. But, thanks to your mechanic’s detective work, we know that’s not true. Something is draining 2 amps continuously — which is more than a working clock and alarm will use.
So, now he needs to figure out what’s draining that current. And he’ll do that using the good old scientific method.
He’ll put his inductive ammeter on one of the battery cables to measure the current in real time. Then he’ll start to disconnect things, one by one, until he sees the current drop.
My first guess would be a bad alternator, which can cause a current drain. It’s got two plugs. He should unplug them both and see if the current drops to a normal load, which should be less than half of what it’s losing now.
If unplugging the alternator doesn’t affect the current, he should then start moving fuses, one at a time. If he pulls out a fuse and the current drops, he knows that something in that circuit is causing the current drain, and he tests the parts individually.
It may turn out to be a short in the alarm system, a faulty voltage regulator or a relay that’s sticking. But, that’s how he’ll find it, Ellen; with good old, methodical trial and error.
Honestly, it’s not fun work. It’s a bit of a pain in the neck. So, he may be hoping your car gets hit by a meteor before you make him find your current draw. So, try plying him with homemade brownies. That always works on me.
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 www.cartalk.com.