Car won’t start: starter not cranking or alternator not charging

When a car won’t start, the key is to work out at what stage it fails: the starter doesn’t turn at all, just clicks, cranks slowly — or the engine turns over but doesn’t fire. In the first cases the cause is usually the battery, the starter, the terminals, or an alternator that isn’t charging the battery while driving. A battery light on the dashboard while driving signals a charging problem, not a battery problem.

How it shows up

• One or more clicks when you turn the key or press the button, but the starter doesn’t crank
• The starter cranks slowly and laboriously, especially in frost
• The battery light is on or flickering while driving
• The battery goes flat overnight or after a few days parked
• Headlights dim, electronics glitch, random warnings appear on the dashboard
• The starter keeps whirring after the engine starts, or spins without engaging

Possible causes

1. 01

   Flat or worn battery

   The simplest cause and the first one to check. But if the battery keeps going flat, you need to find out why: the alternator, a parasitic drain or the battery itself.

2. 02

   Corroded terminals and earth

   Poor contact at the terminals, the starter power cable or the engine earth strap blocks the cranking current — the starter clicks or barely turns.

3. 03

   Starter solenoid and brushes

   Worn solenoid contacts cause clicking without cranking; worn brushes or bushings cause slow or intermittent cranking. Usually repairable.

4. 04

   Starter drive (bendix)

   If the starter whirs but the engine doesn’t turn, or it keeps whirring after startup, it’s most often a faulty starter drive (pinion overrunning clutch).

5. 05

   Alternator: voltage regulator, rectifier, brushes

   The alternator stops charging or overcharges. The battery light comes on and the battery drains while driving, or with overcharging it starts to boil.

6. 06

   Drive belt and parasitic drain

   A broken or slipping belt doesn’t turn the alternator. If the battery dies while parked, something may not be switching off — we find that by measuring the current draw.

How we check

1. 01We check the battery condition, terminals and power cables
2. 02We measure charging voltage at idle and under load
3. 03We check the starter, drive belt and alternator pulley, removing the unit for repair if needed
4. 04If the electronics are glitching, we read the control unit fault codes and, if needed, look for a parasitic drain
5. 05We agree on the unit repair and its cost before starting work