Diagnose a Car Problem

To diagnose car problems, start with the symptom. Each guide below gives a short answer, a table of the most likely causes, what you can safely check yourself and when to go to a shop, with sources from vehicle, battery, brake and lighting manufacturers and government agencies. Both AutoZone and Advance Auto Parts test batteries and scan check engine codes for free, which is often the fastest first step.

Safety first. A red oil pressure light, a brake pedal that sinks or feels soft, or a flashing check engine light means stop driving and get help. Brakes and steering are safety systems; when in doubt, have a professional inspect them.

Won’t start or battery problems

Car clicks but won&#8217Clicking when you turn the key: battery, cables or starter.SymptomCar won&#8217Nothing at all when you turn the key or press start.SymptomWarning lightBattery light on while drivingUsually the charging system, not the battery.SymptomCar battery dies overnightParasitic drain, a weak battery or charging trouble.

Brake problems

SymptomSqueaking brakesWear indicators, glazing, dry hardware or rust.SymptomGrinding brakesOften metal on metal: stop and inspect soon.SafetySpongy brake pedalAir, leaks or low fluid. Get it inspected.GuideHow long do brake pads lastWhy there is no single mileage and how to check.

Warning lights and engine running problems

Warning lightCheck engine light causesSolid vs flashing, common causes and free code scans.Warning lightOil light onRed oil pressure light: stop the engine.SymptomRough idle and misfireSpark plugs, coils and other common causes.

Visibility problems

SymptomWipers streakingWorn rubber, dirty glass or the wrong blade.SymptomDim or flickering headlightsAging bulbs, connections or charging voltage.

Know the part you need? Use the vehicle part finder to search each store for your car, then compare prices by category.