Car won't start: how to tell battery, alternator, starter or fuel pump

When a car won’t start, the sound it makes tells you where to look first. Rapid clicking or a slow crank usually points to the battery or its connections, a single click with bright lights points to the starter, and an engine that cranks normally but never fires is usually missing fuel or spark. A battery that keeps going flat after a jump is often a charging problem, which means the alternator.

That is a starting point, and a test confirms it. The sections below sort the common cases by what you hear and see, explain what you can safely check yourself, and describe how we test each part at Prestige Auto Repairs & Tires.

What the car does when you try to start it

Two of these can overlap. A battery that has been run flat several times is often damaged, so a car can need both an alternator and a battery.

Battery: the most common cause

A 12-volt battery wears out from heat, age and deep discharge. South Florida heat is hard on it, and a battery here often fails with little warning: the car starts fine on Friday and clicks on Monday.

Signs that point to the battery:

• Rapid clicking, or a slow, heavy crank that gets worse each morning
• Interior lights and screens that dim sharply when you turn the key or press start
• Start-stop that has quietly stopped working (on an Audi, see our guide to the start/stop system fault)
• White or green crust on the terminals, or a swollen battery case
• A car that sat for a week or two and will not wake up

A fully charged battery rests at roughly 12.6 volts. A voltage reading alone does not prove the battery is healthy, because a worn battery can show good voltage and still collapse under load. That is why we use a tester that measures the battery’s ability to deliver current, and we check the terminals and grounds at the same time.

On many late-model European cars, a new battery has to be registered to the car so the charging system knows its type and age. BMW requires this, and several other makes have a similar step. See car battery replacement in Fort Lauderdale for the battery types we fit, or battery replacement at our Oakland Park shop.

Alternator: the battery keeps going flat

The alternator recharges the battery and runs the car’s electrical loads while the engine is on. When it stops charging, the car runs on the battery alone until the battery is empty.

Signs that point to the charging system:

• A battery warning light on the dash while driving
• Headlights that dim at idle and brighten when you rev the engine
• Several unrelated warnings at once as voltage falls
• A new or freshly jumped battery that is flat again within a day or two
• A whining noise from the front of the engine, or a squealing belt

On many cars the charging voltage sits around 14 volts with the engine running. Newer cars with smart charging change that figure on purpose to save fuel, so a single low reading is not proof of a fault. We measure voltage and current under load and compare them with what the car’s computer is requesting. Do not disconnect the battery with the engine running to “test” the alternator. On a modern car that can damage control units.

Our alternator and starter repair page covers the charging tests in more detail.

Starter: one click and nothing else

The starter is an electric motor that turns the engine over. It draws more current than anything else on the car, so it is sensitive to weak connections.

Signs that point to the starter:

• A single click from the engine bay with dash lights that stay bright
• A grinding or whirring noise without the engine turning
• A car that starts on some attempts and not on others, often worse when the engine is hot

A weak battery can produce the same click, which is why the battery is tested first. Then we measure the voltage that actually reaches the starter while cranking. If full voltage arrives and the starter does not turn, the starter is at fault. If voltage is lost on the way, the fault is a cable, a ground or a relay.

Fuel pump: cranks but will not fire

If the engine spins at its normal speed and never catches, the battery and starter are working. The engine needs fuel, spark and correct sensor signals to run, and one of them is missing.

The fuel pump is a common cause. Clues include an engine that hesitated or lost power on the highway in the days before, a car that stalled and would not restart, or a no-start that happens only when the engine is hot. On many cars you can hear the pump hum for a second or two from the rear of the car when the ignition is switched on. Silence is a hint, though some cars prime the pump at other times.

Other causes look identical from the driver’s seat: a blown fuse or failed relay, a crankshaft position sensor, a security system that does not recognize the key, or simply an empty tank with a gauge that reads wrong. We read the fault codes, measure fuel pressure, and check that the pump is getting power and a ground before recommending a fuel pump replacement.

Avoid cranking the engine over and over. It drains the battery, heats the starter, and adds a second problem to the first.

What you can safely check yourself

1. Look at the dash. Note which lights come on, whether they dim when you try to start, and any message on the screen.
2. Check the basics. Make sure the selector is in Park, your foot is firmly on the brake, and on a push-button car hold the key fob against the marked spot if the fob battery may be weak. The owner’s manual shows where.
3. Look at the battery terminals if you can reach them. Heavy corrosion or a loose clamp is a finding worth reporting. Do not touch a battery that is swollen, cracked or leaking.
4. Jump-start only by the book. Many European cars keep the battery in the trunk and provide jump posts under the hood. Use the points in the owner’s manual. Hybrids and EVs have their own rules.
5. Write down what happened. The sound, the weather, how long the car sat, and whether a warning light was on beforehand all help the technician.

How we find the cause

1. Battery test for state of charge and state of health, plus a look at the terminals, main grounds and fuses.
2. Starter circuit test: voltage at the starter during cranking and voltage drop across each cable.
3. Charging test with the engine running and electrical loads switched on.
4. Parasitic draw test when a battery goes flat while parked, to find the circuit that stays awake.
5. Scan of every control unit for stored faults, including the immobilizer and engine computer.
6. Fuel pressure and signal checks when the engine cranks but does not fire.
7. Photos and a written estimate that names the cause before any repair starts.

Wiring faults, modules that will not go to sleep and key problems are handled by our auto electrical and key programming service.

Bringing the car in

If the car starts with a jump, drive straight to the shop without switching it off on the way. If it will not start at all, call us first and describe what it does, so we know what to expect when it arrives. The Oakland Park lot is open 24 hours with a key drop box at the front door for after-hours drop-off, and we call you in the morning.

Oakland Park is at 250 NE 44th St, open 7 days from 8 AM to 7 PM, (954) 303-0758. Fort Lauderdale is at 930 NE 4th Ave, open Monday to Saturday from 8 AM to 7 PM, (954) 562-8045. You can also request an estimate and include the sound the car makes when you try to start it.