If your radio plays, the dome light comes on, and your headlights are bright - but the engine will not start - your battery has enough juice for accessories but not enough to crank the starter, OR the starter circuit itself is broken. This narrows the diagnosis to four likely causes: a weak battery under load, a bad starter motor, a failed ignition switch, or a triggered safety interlock.
It takes 200+ amps to crank a starter. Your headlights only pull 10 amps. A battery can light your dash perfectly and still be dead for starting. Get a free load test.
Each cause is rated by likelihood, repair cost range, DIY difficulty, and severity. Start with the highest-probability cause and work down.
Most likely cause. Battery has 12+ volts at rest (enough for lights and radio) but voltage drops below 9V under starter load. Free 5-minute load test at any parts store will confirm.
If you sometimes hear a single click or grinding, the starter brushes or solenoid are worn out. Tapping the starter with a hammer while a helper turns the key is the classic test - if it cranks after a tap, replace the starter.
The big cable from battery positive to starter can corrode at either end. Plenty of voltage reaches the dash but the high-amp starter path is choked. Wiggle and inspect cable ends.
RUN position contacts work fine (giving you radio and dash) but the START position contacts are pitted or broken. Watch warning lights as you turn to START - if they stay rock-solid, the START contacts are dead.
Push-button start cars need the brake pedal pressed firmly. Automatics need solid Park engagement - try jiggling the shifter. Manuals need the clutch fully to the floor.
The solenoid pulls the starter pinion into the flywheel. When it fails open you get nothing or just a faint click. Replace the solenoid (some are integrated with the starter).
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If your scan tool is showing one of these codes alongside this symptom, that is your starting point. Click any code for the full diagnosis.
Not necessarily. The radio only needs about 1 amp. The starter needs 200+ amps. A battery can run accessories all day and still be too weak to crank. Get a load test to know for sure - it is free at every major parts store.
Either the battery cannot deliver high amperage (most common), the starter motor is failed, the high-amp cable is corroded, or the ignition switch START contacts are worn out. All four are common and easy to diagnose in sequence.
Have a helper hold the key in the START position. Tap the body of the starter motor sharply with a hammer or wrench. If the engine then cranks, the starter brushes are worn - replace the starter ($200-500 installed).
Load test the battery first (free at parts stores). If the battery passes but the car still will not crank, it is the starter, the heavy cable, or the ignition switch. If the battery fails the load test, replace it first - it might be the only issue.
Yes, and it often works. The jump provides the high amperage your battery cannot. If it starts after a jump, drive to a parts store immediately for a battery load test.
Battery: $100-250. Starter: $200-500 installed. Battery cable: $20-150. Ignition switch: $80-300 installed. Always rule out the battery before paying to replace anything else.