Starter motors and alternators

The starter motor turns the engine over; the alternator recharges the battery and runs the electrics once it is going.

What starters and alternators means

Both are driven hard and both eventually wear out. Testing which one is at fault is straightforward with a meter, and is worth doing before either is replaced.

What the job covers

Charging system testing
Alternator replacement and reconditioning
Starter motor replacement
Drive belt and tensioner replacement
Smart charging system faults

When you might need it

A single click, or a slow laboured turn, when you turn the key.
The battery warning light staying on while driving.
Lights that dim at idle and brighten when you rev, which points at charging rather than the battery.

What it costs, and what changes the price

Typically £180 to £600.

Where the part sits. Some starters are on top of the engine and some are underneath it, behind the exhaust.
Reconditioned units cost less than new ones and are usually fine.
Smart charging systems on newer cars may need the replacement coding.

How long it takes

An hour or two for an accessible part, most of a day for a buried one.

Common questions

How can I tell which one has failed?

A meter across the battery with the engine running shows whether the alternator is charging. If it charges but the car will not crank, the starter is the suspect.

Is a reconditioned part a false economy?

Not usually. A properly rebuilt unit from a reputable supplier comes with a warranty and costs noticeably less.

Can I keep driving with the battery light on?

Only briefly. The car is running off the battery and will stop when it is flat, which may be a few miles.