Car Won’t Start on Cold Mornings? Battery vs. Alternator vs. Starter

Sacramento winters are mild, but the first cold mornings of the year are when weak batteries finally give up. If your car is slow to start, clicks, or does nothing at all, the problem is usually one of three parts: the battery, the alternator or the starter. Here is how to tell them apart.

Driver checking under the hood after his car won't start on the roadside

Why cold weather exposes a weak battery

A battery makes power through a chemical reaction, and cold slows that reaction down. At the same time, cold oil is thicker, so the engine is harder to turn over. A battery that barely got by in October can fail on the first 35-degree morning. In our area, summer heat does most of the damage, and cold weather is simply when it shows.

Signs it is the battery

  • The engine cranks slowly (“rur… rur… rur”) before starting, or not at all
  • Dash lights are dim or flicker when you turn the key
  • A jump start gets the car going right away
  • White or green crust on the battery terminals
  • The battery is more than 3 to 5 years old

Signs it is the alternator

The alternator recharges the battery while the engine runs. When it fails, the car runs on battery power until the battery is drained.

  • The car starts after a jump but dies again soon after
  • A battery or charging warning light comes on while driving
  • Headlights dim at idle and brighten when you rev the engine
  • A whining or grinding noise from the front of the engine
  • A new battery that keeps going dead

Signs it is the starter

  • A single loud click when you turn the key, but dash lights stay bright
  • Grinding when the engine tries to crank
  • The car starts sometimes and not other times, with no pattern
  • A jump start does not help

What else can drain a battery

If your battery keeps dying overnight, something may be drawing power with the car off. This is called a parasitic drain. Common causes are a glove box or trunk light that stays on, an aftermarket stereo or dash cam, or a module that does not go to sleep. Finding a drain takes testing circuit by circuit. Our auto electrical repair team handles battery drain and wiring problems.

What to check before you call for help

  1. Make sure the car is in Park (or Neutral) and your foot is on the brake.
  2. Look at the dash lights when you turn the key. Dim lights point to the battery. Bright lights with a click point to the starter.
  3. Check the battery terminals for corrosion or a loose cable.
  4. Try a jump start if you have cables and know how to use them safely.
  5. If the car will not start, or starts and dies again, don’t keep cranking. You can overheat the starter.

If the car is stuck, we can arrange towing to the shop.

Don’t ignore warning lights

Charging problems can also turn on the check engine light, because low voltage confuses sensors. If you see both, read our guide to the check engine light and get both checked at the same visit.

Battery and charging test in Rancho Cordova

MPB Auto Repair & Body Shop tests the battery, alternator and starter together, so you only replace the part that actually failed. You get a free written estimate before any work. Call (279) 218-7797 or visit 11432 Elks Cir, Ste B, Rancho Cordova.