Symptoms
- Car occasionally fails to start then works fine later
- Wiggling the battery cable changes whether accessories work
- Clicking sound when the terminal is bumped
- Dashboard lights flicker over bumps
Likely causes
- CommonClamp bolt not tightened enoughVibration over time can loosen a clamp that wasn't torqued properly during a service.
- CommonCorroded terminal preventing a tight seatBuildup under the clamp can prevent full metal-to-metal contact even when the bolt feels tight.
- PossibleWorn or cracked terminal clampAn old clamp can crack and no longer close fully around the post.
What to do
- With the engine off, try gently wiggling each battery terminal by hand; it should not move at all.
- If a terminal moves, loosen the clamp bolt, clean any corrosion off the post and inside the clamp, and reseat it fully onto the post.
- Tighten the clamp bolt firmly with a wrench, but avoid overtightening to the point of cracking the clamp.
- Recheck by trying to wiggle it again; it should now be solid with no movement.
- If the clamp itself looks cracked, corroded beyond cleaning, or won't tighten fully, replace it rather than continuing to use it.
- Start the car and confirm it starts normally and accessories work without flickering.
Tools and parts
- Wrench
- Wire brush
Replacement battery terminal clamp, if neededSearch: “battery terminal clamp replacement”
When to call a pro
If the car still won't start reliably after tightening a clean, solid connection, have the battery and starter tested.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.