Car Problem Symptoms: Signs Something Is Wrong
Each guide lists the most common signs of a failing part in plain words, how urgent each one is, how to confirm it, and which models draw the most NHTSA owner complaints about it.
Updated 2026-11-11 · By CarWhere Research · NHTSA complaints fetched July 13 – September 29, 2026
Engine
Blown head gasket symptomsEngine overheats, or the temperature gauge climbs in traffic or on hills · Coolant level keeps dropping but there is no puddle under the car · Thick white exhaust smoke with a sweet smell that doesn’t clear once warmStop drivingBad spark plugs symptomsRough, shaky idle or the engine “stumbles” · Misfire you can feel as jerking or hesitation, especially under load · Hard starting or long cranking, worse in cold or damp weatherDrive gently — get it checkedBad ignition coil symptomsEngine shakes or idles roughly, often worse at a stop · Jerking, bucking or hesitation under acceleration · Noticeable loss of power, especially uphillDrive gently — get it checkedBad fuel pump symptomsSputtering, jerking or surging at steady highway speed · Loss of power when accelerating, towing or climbing hills · Long cranking or hard starting, especially when the engine is hotDrive gently — get it checkedLow oil / oil pressure symptomsRed oil-pressure warning light (oil-can symbol) on while the engine runs · Ticking or tapping from the valvetrain, especially at start-up · Deep knocking that gets louder with RPM (bearing damage)Stop drivingBad PCV valve symptomsRough, high or unstable idle; possible stalling · Whistling, hissing or moaning from the engine bay (vacuum leak) · New oil leaks at the valve cover, seals or dipstick tubeOK to drive — schedule a check
Cooling
Bad water pump symptomsCoolant drips or crusty green, orange or pink residue at the front of the engine · Temperature gauge climbs or the engine overheats · Whine, squeal or grinding that rises with engine speedStop drivingBad thermostat symptomsEngine overheats or the gauge climbs quickly (stuck closed) · Gauge stays low or takes very long to warm up (stuck open) · Heater blows lukewarm or cold airDrive gently — get it checked
Electrical and starting
Bad alternator symptomsBattery or charging warning light comes on while the engine is running · Headlights and dash lights dim, flicker, or brighten with engine speed · Power windows, radio or heated seats act up or resetDrive gently — get it checkedBad starter symptomsOne loud click and nothing else when you turn the key or press start · Grinding or harsh metallic noise while cranking · Whirring or free-spinning sound, but the engine doesn’t turn overOK to drive — schedule a checkBad battery vs. alternator symptomsBad battery: slow crank, clicking, or no start — but runs fine once jumped · Bad battery: car is 3–5+ years old on the original battery, worse in heat or cold snaps · Bad alternator: battery light on while drivingDrive gently — get it checked
Transmission
Low transmission fluid symptomsA pause or clunk before the car moves after shifting into Drive or Reverse · Slipping: RPM flares up without the car accelerating · Harsh, late or erratic shiftsDrive gently — get it checkedBad transmission symptomsSlipping: RPM jumps but the car doesn’t accelerate · Delay or clunk when shifting into Drive or Reverse · Harsh, late or erratic shifting; stuck in one gear (“limp mode”)Drive gently — get it checkedBad torque converter symptomsShudder or vibration at steady 30–50 mph under light throttle · Slipping: RPM higher than usual at cruise or flares when accelerating · Transmission overheating or a burnt-fluid smellDrive gently — get it checked
Emissions and sensors
Bad catalytic converter symptomsCheck engine light, most often P0420 or P0430 (catalyst efficiency below threshold) · Rotten-egg or sulfur smell from the exhaust · Sluggish acceleration, loss of top speed or stalling (a clogged converter)Drive gently — get it checkedBad O2 sensor symptomsCheck engine light with an O2 sensor code (P0130–P0161) or heater-circuit code · Worse fuel economy than usual · Rough idle, hesitation or surgingOK to drive — schedule a check
Brakes
Worn brake pads & warped rotors symptomsHigh-pitched squeal when braking (pad wear indicator) · Grinding or growling — pads may be worn to the metal · Pulsing pedal or steering-wheel shake when braking (rotor thickness variation)Drive gently — get it checkedBad wheel speed (ABS) sensor symptomsABS warning light on, often with traction control and stability control lights · ABS pulsing or clicking at low speed on dry pavement · Stability or traction control turned off or acting erraticallyDrive gently — get it checked
Steering and suspension
Bad wheel bearing symptomsHumming, growling or “roaring” noise that rises with road speed, not engine speed · Noise gets louder or quieter when you steer or change lanes to one side · Vibration in the steering wheel, floor or seatDrive gently — get it checkedBad tie rod symptomsLoose, vague or “wandering” steering; extra play before the wheels respond · Clunk, knock or rattle from the front when turning or on bumps · Steering wheel shakes or vibrates, sometimes worse when turningStop drivingBad ball joint symptomsClunking or knocking from the front over bumps, potholes or driveways · Squeaking or creaking when turning or going over bumps · Steering wanders or feels loose; car driftsStop driving
Frequently asked questions
Which car symptoms mean stop driving right away?
A red oil pressure light, an overheating engine, a soft or sinking brake pedal or red brake warning light, heavy transmission slipping, smoke or a burning smell, and a flashing check engine light with heavy shaking. Pull over where it is safe and have the car inspected.
How do I find out what is wrong with my car?
Note exactly what you notice and when (cold or hot, at idle or under load, which warning light). Read any stored codes with an OBD-II scanner — many parts stores do it free — then confirm with the checks on each page or have a shop test it.
Where does the complaint data on these pages come from?
From owner complaints filed with NHTSA, the U.S. federal vehicle safety regulator. Each page counts complaints that mention the part across the 194 models in our snapshot. They are counts, not failure rates.
If a light is on right now, start with our dashboard warning lights guide.
General information, not a diagnosis of your vehicle. Follow your owner’s manual and check NHTSA for open recalls before paying for a repair.