Diagnose by symptom
What’s it doing?
Noises
StopGrinding when brakingA grinding noise when you brake usually means the pads are gone and metal is cutting metal.SoonBrakes squealingSquealing brakes usually mean the wear indicator has reached the rotor — a deliberate….SoonSqueal on startupA high-pitched squeal at cold start or under load is the serpentine belt slipping.StopEngine knockingA deep knock that speeds up with the engine can be bearing failure — minutes matter.SoonClunk over bumpsA clunk or knock over bumps is a worn suspension joint or link letting parts move that….SoonHumming rises with speedA hum that tracks road speed and changes when you weave is a wheel bearing; steady drone….
Warning lights
StopCheck engine light flashingA flashing check engine light means an active misfire is dumping raw fuel into the….SoonCheck engine light steadyA steady check engine light means a fault is stored — the code turns guessing into a….StopOil pressure light onThe red oil can light means oil pressure has dropped below survival levels — bearings….SoonBattery light onThe battery light means the alternator stopped charging — the car is running down its….
Smoke & smells
SoonWhite exhaust smokeThin white vapor on cold mornings is normal condensation.SoonBlue exhaust smokeBlue-tinged exhaust smoke means oil is reaching the combustion chambers.SoonBlack exhaust smokeBlack exhaust smoke means the engine is running rich — burning more fuel than the air….SoonSweet smellA sweet, syrupy smell means coolant is leaking — and if it's inside the cabin, the….SoonRotten egg smellA sulfur smell from the exhaust means the catalytic converter is struggling — often….StopBurning smellBurning rubber, hot oil, and burning plastic smells each point at different failures —….
Driving feel
SoonShaking at highway speedVibration that appears at 55–70 mph and fades either side is classic wheel imbalance.SoonShakes when brakingA steering wheel that pulses under braking points at uneven brake rotors.SoonPulls to one sideA car that drifts or pulls left or right — the causes in the order they're actually….StopBrake pedal soft or sinkingA soft or sinking brake pedal means the hydraulic system is not holding pressure.SoonTransmission slippingSlipping, flaring RPM, or harsh shifts — check the transmission fluid before believing….SoonRough idle or stallingAn engine that shakes at idle or stalls at stops has an air, fuel, or spark problem that….
Won't start
SoonWon't start — clickingRapid clicking usually means a weak battery; one loud clunk points at the starter.SoonWon't start — silenceTotal silence when you turn the key means the start signal never reached the starter.
Leaks & overheating
SoonFluid leak under carA cardboard sheet overnight identifies most car leaks: color and position name the fluid.StopEngine overheatingAn overheating engine can destroy itself in minutes.
Check engine codes
Got the code read? Look it up.
Most US parts stores read codes free. The code names the faulted system — these guides tell you what it means, what it costs, and where shops most often get it wrong.
P0420Catalyst System Efficiency Below Threshold (Bank 1)P0300Random / Multiple Cylinder Misfire DetectedP0301–P0306Cylinder-Specific Misfire Detected (Cylinders 1–6)P0171System Too Lean (Bank 1)P0442EVAP System Small Leak DetectedP0128Coolant Temperature Below Thermostat Regulating TemperatureP0700Transmission Control System Malfunction (Request Code)C0035Left Front Wheel Speed Sensor Circuit
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Vehicle failure intelligence
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Guides
What it should cost, and how not to get played
What Car Repairs Actually Cost: A Realistic 2026 Price GuideWhat common car repairs actually cost in 2026 — brakes, alternators, water pumps, transmissions —…9 min read
How to Not Get Ripped Off at the Mechanic: A Practical DefenceThe specific upsells, misdiagnoses and pressure tactics that cost drivers money — and the exact…10 min read
The Check Engine Light: A Complete, Non-Panicking GuideEverything the check engine light means — steady versus flashing, the most common codes, what's…11 min read
Choosing an OBD2 Scanner: What Actually Matters (and What Doesn't)How to choose an OBD2 scanner — what code readers, Bluetooth dongles and bidirectional tools…10 min read
The Car Maintenance Schedule That Actually Prevents FailuresA realistic maintenance schedule by mileage — what genuinely prevents breakdowns, what shops…10 min read
Used Car Inspection: The Checks That Find the Expensive ProblemsA practical used car inspection checklist — the cold start test, fluid checks, scanner tricks and…11 min readHow carfailure.com calls it
The method behind the verdicts
Safety first, always
Brakes, steering, overheating, a flashing check engine light — safety-critical patterns resolve to the strict verdict by fixed rules. Nothing softens a stop-now into a maybe.
Honest cost bands
Wide US independent-shop ranges, parts and labour — because a national number pretending to be precise is a lie with decimals. Dealers run higher. Your region moves the band.
The misdiagnosis, named
Every code guide names where the money classically goes wrong — the $2,000 converter condemned for a $250 sensor's fault. Knowing the pattern is most of the defence.
No side deals
No shop referral fees, no parts affiliate links, no pay-to-rank. Nobody pays to change an answer, so the answer is the answer.