The People's Guide to Why Your Car Won't Start

Steve Rogers and Carl Franz wearing sombreros.

Steve Rogers and Carl Franz reclining in front of a beloved Datsun chariot.

editor’s note: El Codo is a retired lead acid battery design engineer and battery performance tester

You don’t need any tools or mechanical “savvy” to do this diagnostic. Print this page out. Fold it, and stick inside the glove box. If you turn the key and your car plays possum, calmly sit back and breeze through this diagnostic checklist.

Let’s Diagnose!

  • If you turn the key and the starter motor whirrs but does not start the engine, it means the starter motor is working OK but for some reason the motor is throwing a hissy-fit. Fold this page back up and start looking for a helper or a mechanic. Your no-start problem is a horse-of-another-color. Sorry.

  • But if you turn the key and nothing happens (but perhaps a click or a buzzing sound), then keep reading.

  • Do the interior lights shine with the door open? If the answer is yes, at least the battery isn’t completely dead. Switch on the headlights. Are they burning bright? If yes, great! Go back inside and switch the lights off.

  • With an automatic transmission sometimes the safety start switch gets corroded, especially if you’ve been hanging out at the beach. Turn the ignition key far enough to allow the shift lever to be moved. Then “range” the shift lever back and forth through all the gears, multiple times. You are wiping the switch electrical contacts clean, hopefully enough to cure a corroded contact. Now try to start the car. If the motor cranks sometimes after “ranging” the shift lever, tell the mechanic you have a flaky neutral safety switch. Malo switch-neutral de seguridad.

  • Many manual transmission cars have a safety clutch switch. If so, stomp on the clutch pedal a half dozen times. For the last pump, slide your foot off the clutch pedal when it’s on the floor and let it sproing back hard. This ought to clean balky switch contacts. Twist the key and see if this trick worked. Most Mexican mechanics will bypass this switch in order to “cobble-repair” it. Get a new switch installed when you get home and be extra careful when starting the car.

  • With an automatic transmission, move the shift lever to “N,” then twist the key and wiggle the lever in the “N” position with the key twisted to the “start” position. Sometimes the neutral safety switch plain wears-out in park but allows the engine to start in the “N” position. This fix works so often it is a real eye-opener.

  • Still no joy? Have a helper stand ahead of the car but safely to one side in order to look at the headlights. Turn the lights on. Do the headlights light up nice and bright? If your helper’s answer is “Yes!” leave the lights on and then twist the key to “start.” What do the lights do? If they stay bright or dim just a little, you need to start looking for the local handyman to lend assistance with more advanced troubleshooting checks. You’ve already tried the shift lever wiggling trick above. Proceed to the next step.

  • If you twist the key and the bright headlights suddenly blink out, then you have a bad battery cable connection. Do this test several times to be sure. When you try to crank the engine, do the lights simply go dead until the key is released? Dirty battery cable connections almost certainly. Sometimes there is also a feeble clicking sound. No matter! If those lights “bounce right back nice and bright the instant you release the key, there’s little doubt you are facing nothing more than annoying dirty battery cables.

  • 90% of the time a “no-start” corroded battery cable connection happens at the joint between the stubby round lead battery post and the lead battery cable “clamp” terminal. See if you can twist an unexpectedly loose cable back and forth. Try both the positive and the negative terminal cables. If they’re loose, twisting them back and forth could scrape them just clean enough to get the car started so you or someone else can clean the terminals and re-tighten them properly. Mechanics, friends and do-it-yourself former car owners frequently forget to tighten cables and thus an eventual no-start is an almost inevitable result. If you find a loose cable problem a mechanic can fix it in a jiffy, or you can tighten it yourself.


  • NOTE: If you do the headlight test and the lights dim a little, over and over again as you turn the key to the start position repeatedly, you probably have a worn-out starter motor. Well, hell, at least you found the problem. Usually worn-out starter motors give plenty of advance warning – you turn the key and nothing happens, but when you try to start the car again, the starter motor works normally. The “yes-then-no cranking quirk” will get more and more common.

  • Battery terminals that have frozen themselves tight to the stubby battery post with icky white or green corrosion are sometimes tough to remove. Try dousing the terminals with boiling water laced with lots of baking soda. Baking Soda in México is called “Bicarbonado de Sodio”. Hell, I’ve seen a shaken-up bottle of Coca-Cola strip corrosion off a battery terminal (Dang, beer doesn’t work too good). The corrosion is going to foam. Good! A crescent wrench or vice grip pliers can loosen the nut. A screwdriver or even a tire iron point can be wedged into the slot of the cable clamp to help pry the cable clamp apart wide enough to slip the terminal off the post. (Be careful with tools, they can cause a damaging short circuit if they touch a body part or the engine.)

  • A sharp knife or really coarse sandpaper can be used to scrape crystal hard black corrosion from inside the battery terminal hole and from the outside of the battery post. Shield your eyes! Those little chips of corrosion that fly off can raise hell with your eyes!

  • If none of the above works and you end up needing a jump start to get the car started, drive to a taller de mechanico (a mechanic’s workshop) to get the car checked out.

  • A battery found to be “flat” because of lights not being switched off or too many hours playing Jimi Hendrix or Los Halcones de Tijuana will need to be jump started then recharged by a battery charger or recharged by lots and lots of driving. It takes two solid-hours, of continuous driving (not idling!), no stops and starts, to recharge a flat battery. Sometimes it’s just smarter to let a mechanic’s shop recharge a battery while you go shopping. Flat batteries need almost two hours of battery charger time to charge all the way back up. There is no way to hurry it up.


  • Boiling hot water and baking soda works best to dissolve corrosion on terminals and posts. Chemistry 101: Heating water makes the baking soda 100-times as potent a corrosion eater–the cleaning power improvement is near phenomenal. Keep a pan of water simmering hot and use a lot of caution as you dribble the water and baking soda mix over the terminal. Keep the battery filler lids on tight as you pour the water and baking soda over the terminals. Slow and easy does it. The corroded terminal and post will stubbornly keep foaming green or purple color for a surprisingly long time. Keep dribbling boiling hot solution until the last bit of off-color foam stops appearing. Then flush with clear water. Corrosion is like cancer, unless you remove every last bit of it, it comes back like a bad penny. The secret, is to take your time. I have used almost a full box of soda and three quarts of boiling water to strip corrosion off a horribly corroded pair of terminals–a twenty minute process of dribbling solution until the white foam stops turning discolored.

  • Hardware stores (ferreterias) sell inexpensive wire brushes and sandpaper. Buff the outside of the terminal until it gleams. The inside of the terminal, the hole, is most easily cleaned with brutally coarse sandpaper lija bravo. Same goes for the stubby lead battery post. If the cable terminal is a goner, replace it with one of those bolt-on emergency battery cable ends with the two little clamping bolts. Shine the stripped copper cable wire until it gleams like a new penny before you clamp on the new cable end.

  • A big surprise to a lot of people is that the overwhelming majority of corrosion fumes do not come from the battery vents. Fumes seep up through the tight joint where the lead battery post sticks up through the plastic battery case lid. This joint needs to be gasketed with a “washer” gobbed with grease to eliminate further corrosion damage. Greasy terminals is a small price to pay to insure cleaned terminals don’t re-corrode quickly. Yuck, one cleaning is enough!

*Don’t worry about “Contaminating” the battery posts and terminal ends with grease. It does not matter if they are greasy! A greasy electrical contact area will not cause a bad connection. This is fact not theory. Grease! Grease! Grease! Go for it!


One Response to “The People's Guide to Why Your Car Won't Start”

Read below or add a comment...

  1. Lorena says:

    Sounds like really good information Senor Codo, but I really hope I never have to use any of it. But in case I do, thanks.