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Car just dies sometimes

I drive an '01 Mitsubishi Montero. It’s check engine light came on, so I took it to my mechanic and he ran a diagnostic on it and told me I needed new catalytic converters. A muffler guy I took the car to for a 2nd opinion said they were fine. He also checked the 02 sensors and said they were fine. I took it back and had my mechanic run another test and he found nothing wrong with the car. One day the car would not start at all, so I banged on the battery posts and it started right up, and the check engine light was off. Now, it won’t start sometimes, or will die while I drive it. Banging on the posts fixes this temporarily, but nothing seems to fix the problem permanently, and no one can tell me what is wrong with the car at all. Help!

How old is the battery? If it is over four years, I would just replace it. If it is newer and you want to save a few dollars, then I would suggest removing the cables (one side of one cable at a time) and clean both services of each end of each cable.

If the CEL returns, get the actual code, many auto part stores will do it for free. It should be in the format [P0123]. Post the number back here. Remember, if it says there is an unexpected result from an O? sensor, don’t assume it means a bad sensor, it is more likely just a poor connection or maybe something else.

Thanks! By the way, could it be I need to replace the entire battery cables, or maybe just replace the sparkplugs?

Since you say nothing about jump-starting your car, start by cleaning the electrical connections at the battery terminals, then if that doesn’t work, replace the battery, if that doesn’t work, replace the cables to the battery.

Also replace your mechanic, unless you didn’t share this information with him.

Why would you think the sparkplugs are the problem.

Because I know nothing about cars…

It’s not a good idea to bang on the battery posts with anything. Lack of battery post maintenance causes a lot of grief to car owners but it is such a simple thing to care for. Removing the cables and cleaning the connection surfaces with a battery post cleaning brush is what should be done first when you have problems like this. Batteries need real respect as they can explode under certain conditions. Some folks have been serverely injured by a battery explosion.

The trouble with the engine dieing may be due to a electrical problem with the ignition or the fuel delivery system.