# What is your car doing? Pick the symptom that matches. Each page ranks the causes, tells you how to confirm each at home, what the fix costs and whether you can keep driving. ## Air conditioning and heat | Symptom | Most common cause | Verdict | | --- | --- | --- | | [Why is my car AC blowing warm air?](/symptoms/ac-blowing-warm-air) | Low refrigerant from a leak | Safe to drive | | [Why does my car AC smell bad?](/symptoms/ac-smells-bad) | Mold and bacteria on the evaporator | Safe to drive | ## Exhaust and smoke | Symptom | Most common cause | Verdict | | --- | --- | --- | | [Why is black smoke coming from my exhaust?](/symptoms/black-smoke-from-exhaust) | Faulty air flow, coolant temperature or oxygen sensor | Drive to a shop this week | | [Why does my car smell like rotten eggs?](/symptoms/car-smells-like-rotten-eggs) | Failing or overloaded catalytic converter | Drive to a shop this week | | [Why is white smoke coming from my exhaust?](/symptoms/white-smoke-from-exhaust) | Condensation on a cold start | Drive to a shop this week | [All exhaust and smoke symptoms ->](/symptoms/exhaust) ## Engine | Symptom | Most common cause | Verdict | | --- | --- | --- | | [Why is blue smoke coming from my exhaust?](/symptoms/blue-smoke-from-exhaust) | Clogged or stuck PCV valve | Drive to a shop this week | | [Why does my car smell like something is burning?](/symptoms/burning-smell-from-car) | Oil leaking onto the exhaust (burnt oil smell) | Drive to a shop this week | | [Why does my car crank but not start?](/symptoms/car-cranks-but-wont-start) | No fuel delivery (fuel pump, fuse or relay) | Drive to a shop this week | | [Why does my car hesitate when I accelerate?](/symptoms/car-hesitates-when-accelerating) | Worn spark plugs or failing ignition coils | Drive to a shop this week | | [Why does my car jerk when I accelerate?](/symptoms/car-jerks-when-accelerating) | Misfire from worn spark plugs or ignition coils | Drive to a shop this week | | [Why is my car leaking oil?](/symptoms/car-leaking-oil) | Leaking valve cover gasket | Drive to a shop this week | | [Why does my car lose power when accelerating?](/symptoms/car-loses-power-when-accelerating) | Misfire from worn spark plugs or a failing coil | Drive to a shop this week | | [Why does my car shake at idle?](/symptoms/car-shakes-at-idle) | Misfire from worn spark plugs or a weak ignition coil | Drive to a shop this week | | [Why does my car shake when I accelerate?](/symptoms/car-shakes-when-accelerating) | Worn inner CV joint or damaged axle | Drive to a shop this week | | [Why does my car smell like gas?](/symptoms/car-smells-like-gas) | Loose, damaged or missing gas cap | Stop driving | | [Why does my car stall while driving?](/symptoms/car-stalls-while-driving) | Failing crankshaft position sensor | Stop driving | | [Why is my engine knocking?](/symptoms/engine-knocking-noise) | Spark knock (pinging) from fuel igniting too early | Drive to a shop this week | | [Why is my car getting bad gas mileage?](/symptoms/poor-gas-mileage) | Underinflated tires | Safe to drive | | [Why is my car idling rough?](/symptoms/rough-idle) | Worn spark plugs or a failing ignition coil | Drive to a shop this week | | [Why does my car squeal when I start it?](/symptoms/squealing-noise-when-starting) | Worn, glazed or stretched serpentine belt | Drive to a shop this week | [All engine symptoms ->](/symptoms/engine) ## Brakes | Symptom | Most common cause | Verdict | | --- | --- | --- | | [Why do my brakes make a grinding noise?](/symptoms/brake-grinding-noise) | Brake pads worn down to metal | Stop driving | | [Why does my brake pedal go to the floor?](/symptoms/brake-pedal-goes-to-floor) | Leaking brake hose, caliper or wheel cylinder | Stop driving | | [Why does my car shake when I brake?](/symptoms/car-shakes-when-braking) | Uneven brake rotors (often called warped) | Drive to a shop this week | | [Why are my brakes squeaking?](/symptoms/squeaky-brakes) | Pad wear indicator touching the rotor | Drive to a shop this week | [All brakes symptoms ->](/symptoms/brakes) ## Battery, starting and electrical | Symptom | Most common cause | Verdict | | --- | --- | --- | | [Why does my car battery keep dying?](/symptoms/car-battery-keeps-dying) | Old or worn-out battery | Drive to a shop this week | | [Why does my car click but not start?](/symptoms/car-clicks-but-wont-start) | Weak or discharged battery | Drive to a shop this week | | [Why won't my car start?](/symptoms/car-wont-start) | Weak or dead battery | Drive to a shop this week | | [Why are my headlights flickering?](/symptoms/headlights-flickering) | Failing headlight bulb or HID ballast | Drive to a shop this week | [All battery, starting and electrical symptoms ->](/symptoms/electrical) ## Cooling and overheating | Symptom | Most common cause | Verdict | | --- | --- | --- | | [Why is my car heater not working?](/symptoms/car-heater-not-working) | Low coolant from a leak | Drive to a shop this week | | [Why is my car leaking coolant?](/symptoms/car-leaking-coolant) | Cracked hose or loose hose clamp | Drive to a shop this week | | [Why is my car overheating?](/symptoms/car-overheating) | Low coolant from a leak | Stop driving | | [Why does my car smell sweet?](/symptoms/sweet-smell-from-car) | Leaking radiator hose, radiator or cap | Drive to a shop this week | [All cooling and overheating symptoms ->](/symptoms/cooling) ## Transmission | Symptom | Most common cause | Verdict | | --- | --- | --- | | [Why is my car leaking transmission fluid?](/symptoms/car-leaking-transmission-fluid) | Leaking transmission pan gasket or loose pan bolts | Drive to a shop this week | | [Why won't my car go into gear?](/symptoms/car-wont-go-into-gear) | Brake light switch or shift interlock fault | Drive to a shop this week | | [Why is my transmission slipping?](/symptoms/transmission-slipping) | Low or burnt transmission fluid | Drive to a shop this week | | [Why does my car whine when I accelerate?](/symptoms/whining-noise-when-accelerating) | Low fluid or a failing power steering pump | Drive to a shop this week | [All transmission symptoms ->](/symptoms/transmission) ## Steering and suspension | Symptom | Most common cause | Verdict | | --- | --- | --- | | [Why does my car pull to one side?](/symptoms/car-pulls-to-one-side) | Low or uneven tire pressure | Drive to a shop this week | | [Why does my car make a clicking noise when I turn?](/symptoms/clicking-noise-when-turning) | Worn outer CV joint | Drive to a shop this week | | [Why is my steering wheel hard to turn?](/symptoms/steering-wheel-hard-to-turn) | Low power steering fluid from a leak | Drive to a shop this week | [All steering and suspension symptoms ->](/symptoms/steering) ## Tires and wheels | Symptom | Most common cause | Verdict | | --- | --- | --- | | [Why does my car make a humming noise while driving?](/symptoms/humming-noise-while-driving) | Worn wheel bearing | Drive to a shop this week | | [Why does my steering wheel shake at high speeds?](/symptoms/steering-wheel-shakes-at-high-speed) | Tires out of balance | Drive to a shop this week | | [What causes uneven tire wear?](/symptoms/uneven-tire-wear) | Wheel misalignment | Drive to a shop this week | [All tires and wheels symptoms ->](/symptoms/tires) ## Warning lights - [ABS warning light](https://diagxcar.com/warning-lights/abs) - [Airbag (SRS) warning light](https://diagxcar.com/warning-lights/airbag) - [Battery (charging system) warning light](https://diagxcar.com/warning-lights/battery) - [Brake warning light](https://diagxcar.com/warning-lights/brake) - [Check engine light](https://diagxcar.com/warning-lights/check-engine) - [Coolant temperature warning light](https://diagxcar.com/warning-lights/coolant-temperature) - [Oil pressure warning light](https://diagxcar.com/warning-lights/oil-pressure) - [Power steering warning light](https://diagxcar.com/warning-lights/power-steering) - [Tire pressure (TPMS) light](https://diagxcar.com/warning-lights/tire-pressure) - [Traction control light](https://diagxcar.com/warning-lights/traction-control) --- Source page: https://diagxcar.com/symptoms General information, not a substitute for a qualified mechanic.