For Phantom Car Issues, Check the 'Pending Codes'

Dear Car Talk:

I have a 2004 Saturn Vue with a Honda V-6 engine and 150,000 miles. I bought the car with 54,000 miles on it. I have no significant problems with it except that when going uphill at about 1,700 to 1,900 rpm, there is a slight "stutter" in the engine.

My mechanic, who is a great, honest guy, cannot get the engine to do this despite several test drives. A friend advised me to change the transmission fluid. What do you think? -- Mark

Changing the transmission fluid is like chicken soup, Mark. It can't hurt. But I think it's much more likely you have what we call a "miss."

Not to be confused with the Saturn Vue, a vehicle that was widely considered to be a "miss" for Saturn. A miss is an engine misfire. It's most likely to be noticed when the engine is under load, like when you're climbing a hill. It's often electrical in nature and usually easy to fix -- once you can find and identify the cause.

Normally, an engine miss will turn on your car's "check engine" light and store a fault code in the computer. Your mechanic would then use his scan tool to check the code, which will tell him what part has malfunctioned.

But if a problem is intermittent and of short duration, the computer might consider it a phantom event, and not store a code or turn on the check engine light.

In that case, it may store the information as a "pending code." That's information about something that went wrong, but it hasn't happened regularly enough to become a pattern yet. So ask your mechanic to check for pending codes.

Misfires are most often caused by bad spark plugs, bad plug wires or bad ignition coils. Those all are part of what we call the secondary ignition system. And you'll be glad to know none of that is home equity line of credit level stuff.

If there are no pending codes, you can wait until the problem gets worse, at which point it will turn on your check engine light. Or, if they're due to be changed anyway -- and, at 150,000 miles they probably are -- you can take a guess and replace the plugs and wires and see what happens. Good luck.

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