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15 Car Problems You Can Diagnose (and Fix!) Yourself

Some car problems require a professional diagnosis and repair. But there are many car problems you can diagnose and fix on your own. Here are the top car problems any DIYer can fix.

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OilPhoto: I. Pilon/Shutterstock

Oil Warning Light is On

An oil warning light is one of the most serious car problems you’ll ever encounter. When the light (or oil icon) comes on, you should immediately pull over and shut off your engine. The low pressure warning light can be mean you’ve got a bad oil pressure sensor, bum oil pump or a significant engine wear problem. But it can also mean that you’ve simply run out of oil. You can check your oil level right there on the side of the road.

Grab a rag or tissue, pop the hood and remove the dipstick (check your owner’s manual if you don’t know where it is). Wipe the dipstick with the rag and re-insert it into the dipstick tube, making sure it seats all the way (goes all the way in). Then pull it out again to check your oil level. You’ll see two marks, notches or holes on the dipstick indicating the “FULL” and “ADD” levels. If the oil appears below the ADD mark, you’re out of oil. Call a friend and ask them to pick up at least four quarts of the proper oil (find the oil specs for your car on the oil filler cap or in the owner’s manual). Add just enough oil to bring the oil level up to the full mark on the dipstick. Then drive your car to a shop to have it checked for leaks or an oil consumption issue.

However, if the dipstick test shows your oil level is above the ADD mark, the problem is too serious to address on the side of the road. Call a tow truck and have your car brought to a shop for a professional diagnosis.

Try this simple hack and you’ll never miss another oil change.

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EnginePhoto: Bjoern Wylezich/Shutterstock

Diagnose a Check Engine Light

A “Check Engine” or “Service Engine Soon” or “Reduced Power” light or warning message on your dash means your car’s computer has detected a problem with the engine or transmission and stored a trouble code in its memory. In most cases, the problem is caused by a faulty sensor that you can probably replace yourself. But, first you have to get the trouble code from the computer. Many auto parts store will read the trouble code for free. Or, you can buy a scan tool/code reader and pull the codes yourself. A scan tool costs less than the price of a single professional diagnostic charge. Once you have the code, search the Internet for advice on fixing that particular code. For example, a search for “P0171 Ford Focus” turns up hundreds of results; both step-by-step articles and YouTube videos. Follow that free advice and you’ll most likely get all the information you need to fix the problem.

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Photo: Family Handyman

Fix a Dim Headlight

Most DIYers think a dim headlight is caused by a poor connection on the power side of the circuit. That’s possible, but in most cases the dim headlight is caused by corrosion on the ground connection. So check the electrical connector for corrosion and then clean the ground connection.

Remove the electrical connector that plugs into the headlight. Look for signs of corrosion or melted plastic from excessive heat. If you find corrosion, clean it using electrical contact cleaner and a small wire brush. If the connector is melted, purchase a new pigtail headlight connector from any auto parts store or dealer parts department and splice it into the wiring harness. Next, clean the headlight ground connection. To locate the connection, simply follow the ground wire to its termination on the frame or fender. Remove the screw or bolt, clean off the rust, apply a dab of dielectric grease and reconnect. Then turn on the headlights. If they’re bright, you’re done. If not, you’ll need a professional diagnosis.

Check out these five headlight upgrades for better style, safety and performance.

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Photo: Family Handyman

Fix a Slow Moving Power Window

A sticky, slow moving power window can be really frustrating, especially at a toll booth or drive-thru window. You can usually fix the problem by lubricating the window channels. But if you don’t fix the problem, the slow-moving window will stress the window regulator mechanism until it breaks, costing you around $400 to replace.

Here’s the fix. Buy an aerosol can of dry Teflon spray. It sprays on as a liquid but dries to a white slippery Teflon powder. Shake the can vigorously to mix the Teflon particles with the solvent. Insert the straw into the nozzle and aim the spray into the window channels. Press the trigger and soak the front and rear channels until the spray runs down into the door. Wait a few minutes for the solvent to evaporate, then operate the window up and down several times to spread the dry Teflon spray through the channels.

This genius hack will keep your car windows from fogging up.

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Photo: Family Handyman

Fix a Squealing Belt

Of all the car problems you might encounter, a squealing belt is probably the most annoying. The high-pitched squeal is produced when the rubber belt loses its grip and slips around the pulleys. In rare cases, a worn slow-moving alternator, pump or AC compressor bearing or component misalignment can cause a perfectly good belt to squeal. But in most cases, the belt slips because it’s worn, is loose or has been contaminated with oil or coolant. You can diagnose all those problems yourself with a visual inspection, a belt wear gauge and a spray water bottle.

First, check the belt for wear using a belt wear gauge (around $8). If the belt is worn, replace it. Next, try to recreate the conditions when the belt squeals (first thing in the morning when the engine is cold, when you accelerate, etc.). Start the engine and spray a stream of water on the ribbed side of the belt before it wraps around each pulley. If the noise disappears but comes back in a few minutes, the belt or the components it drives are misaligned. That’s not something you can fix on your own. Take it to a shop.

However, if the noise gets louder after the water spray, the belt has too little tension. If your vehicle has an automatic belt tensioner, replace the tensioner. If it has manual tension adjusters, tighten the belt slightly and re-test.

Here’s what you need to know about your accessory belt drive system.

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car won't start shoe to battery terminalPhoto: Family Handyman

Car Won’t Start

If you turn the key and hear a single click or rapid clicking but the engine doesn’t crank (rotate), chances are you’ve got a weak or dead battery or corroded battery terminals. Since you probably won’t have the right tools with you when your engine won’t start, here are two easy ways to get up and running.

Car batteries make power through a chemical reaction and that reaction slows down in cold weather. If you can warm up the battery, you can increase battery output. You can warm up the battery simply by turning the key to start several times, with a five-minute rest period between each try. Here’s how to do it. Turn the key to the START position and hold it in that position for about five seconds. Turn the key to off and wait five minutes. Repeat six more times. If it doesn’t start on the last try, move on to the shoe trick below.

Remove your shoe and tap each battery terminal with the heel. Then try starting the engine. If it starts, clean the battery terminals as soon as you get home.

Don’t miss these 13 ways you’re shortening the life of your car.

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Photo: Family Handyman

Fix a Sticking Hood Latch

Hood latches are pretty simple mechanisms, but they’re constantly exposed to water, salt and road grit, and that can make them gum up, rust and stick. Sometimes the problem is so bad you can’t even pop the hood. Here’s how to fix a sticking hood latch.

Buy a can of aerosol rust penetrant and a can of spray white lithium grease. Start by soaking the latch mechanism with the rust penetrant. If you can’t open the hood at all, slide the spray straw into the grille and aim it up toward the latch. Then shoot about a half can of lube onto the latch. Let it soak for an hour. If it opens after that, move on to the next step. If not, repeat the procedure.

Once the hood opens, soak the hood latch mechanism with white lithium grease. Then close and open the hood multiple times until the latch works smoothly. Apply fresh grease every year before winter.

These are the craziest things car mechanics have seen on the job.

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Photo: Family Handyman

Fix Poor Acceleration

Your car’s computer relies on the Mass Airflow Sensor (MAF) to detect the volume, mass and temperature of the air entering your engine. It then calculates the proper amount of fuel to add. However, if the sensing elements inside the MAF are dirty, the computer gets skewed readings and miscalculates how much fuel to add, and that causes performance issues.

Most MAF sensors can be restored to full operating condition with a simple cleaning. To clean your MAF sensor, buy a can of MAF Sensor Cleaner from any auto parts store. Remove the sensor from the air duct by loosening the worm drive clamps with a screwdriver or socket. Then aim the spray cleaner directly at the sensing elements inside the MAF housing. Soak the sensing elements but don’t touch them with your fingers, rag or brush—they’ll break. Let the solvent dry, then reinstall the MAF.

If a dirty sensor was causing your acceleration problem, the cleaning should put you back in the groove. If not, get it checked out by a pro.

Don’t forget about these 13 weird car features you didn’t know you might have.

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