Car won't start due to a loose battery terminal

Symptoms

• Clicking, dimming lights, or complete silence when starting
• Terminal clamp can be wiggled or rotated by hand
• May have recently had battery or other under-hood work done
• Problem may come and go depending on how the car was last parked or driven over bumps

Likely causes

• CommonBattery terminal clamp not tightened enoughA loose clamp increases resistance and can lose contact entirely under vibration.
• PossibleTerminal clamp corroded in addition to being looseCorrosion often accompanies looseness and compounds the connection problem.
• Less commonBattery post itself worn or damagedA worn post can prevent the clamp from gripping securely even when tightened.
• Less commonIncorrect or damaged replacement clamp installedAn ill-fitting aftermarket clamp may never seat as securely as the original.

What to do

1. With the car off, check both battery terminals by hand to see if either clamp can be twisted or lifted off easily.
2. If a terminal is loose, tighten the clamp bolt with the appropriate wrench until it can no longer be moved by hand.
3. Check that the clamp is seated as far down on the post as it will go before tightening, rather than perched on top.
4. Clean any corrosion off the terminal and post with a wire brush before retightening, since corrosion can prevent full seating.
5. Try starting the car after tightening to confirm this resolves the issue.
6. If the post itself looks worn, corroded through, or damaged, consider having the cable end or terminal replaced rather than just tightened.
7. Recheck the connection after driving over rough roads for a day or two to make sure it stays tight.
8. Have a mechanic inspect if tightening doesn't fully resolve the intermittent starting problem.

Tools and parts

• Wrench for terminal clamps
• Wire brush

When to call a pro

If tightening a loose terminal doesn't fully fix the intermittent no-start, have a mechanic check the terminal, post, and cable ends more closely.

Safety