WhatIsWrongWithMyCar.com — AI Car Diagnosis & Repair Knowledge Base
WhatIsWrongWithMyCar.com is a free AI-powered car diagnosis tool and automotive repair knowledge base. Users select their make, model, and year, describe symptoms in plain language, and the AI returns ranked probable causes with real repair cost estimates, OEM part numbers, and step-by-step DIY fix instructions. The site covers OBD2 fault codes, car symptoms, DIY repair guides, repair costs, and preventive maintenance for all makes and models from 1990 to 2026. Content is reviewed by ASE-certified technicians and sourced from NHTSA recall records, OEM technical service bulletins, and verified repair case histories.
Core Tools
AI Car Diagnosis Tool — free, no sign-up; input make/model/year + symptoms for ranked causes, costs, and DIY guides
OBD2 Code Library — every P, B, C, and U code explained with causes, symptoms, urgency, and fixes
Car Repair Cost Guide — DIY vs shop prices for 50+ common repairs, verified US market data
Repair Cost Calculator — interactive tool for instant DIY vs shop cost breakdown
2026 Repair Cost Index by State — original research for all 50 US states; national average $478/year
Tire Size Finder — OEM tire specs, load index, speed rating, and PSI by vehicle
VIN Lookup — decode any VIN, check NHTSA recalls and service campaigns
Preventive Maintenance Schedule — every service interval, cost, and consequence of skipping
Fuel Pump Failure, Wheel Bearing Noise, Suspension Clunk Noise, AC Not Cooling
Popular OBD2 Code Guides
P0300 Random/Multiple Cylinder Misfire, P0420 Catalytic Converter Efficiency, P0171 System Too Lean, P0301 Cylinder 1 Misfire
All content is for diagnostic guidance only. Safety-critical repairs should be inspected by a licensed mechanic.
Symptoms of Bad Car Parts: Complete Guide to Identifying Failed Components
Common Component Failures
Bad alternator: dimming lights, battery warning, stalling. Bad fuel pump: no start, stalling, loss of power under load. Bad catalytic converter: rattling, sulfur smell, failed emissions. Bad wheel bearing: humming or grinding that increases with speed. Bad ignition coil: misfire, rough running, flashing check engine light.
Why Early Detection Matters
Recognizing symptoms of a failing part before it fails completely prevents breakdowns, expensive secondary damage, and unsafe driving conditions. Use the AI diagnosis tool with your specific symptoms for a ranked cause list.
Bad Spark Plugs — Symptoms and Replacement
Worn spark plugs cause rough idle, hesitation under acceleration, reduced fuel economy, hard starting, and a flashing or steady check engine light with misfire codes P0300 through P0308. Spark plugs fire thousands of times per minute — over tens of thousands of miles, the electrode erodes and the gap widens, weakening the spark. Symptoms appear gradually, so many drivers do not notice until fuel economy drops or a misfire code appears. Replacement cost: $20 to $60 in parts for a 4-cylinder engine DIY, $100 to $250 at a shop. Replace at the manufacturer interval: 30,000 miles for copper, 60,000 to 100,000 miles for iridium or platinum.
Bad Thermostat — Symptoms and Replacement
A stuck-open thermostat causes the engine to run cold, the temperature gauge to stay low, poor fuel economy, and the heater to blow lukewarm air. A stuck-closed thermostat causes rapid overheating, the temperature gauge to spike into the red, and steam from under the hood. The thermostat is a simple valve that opens at a specific temperature to allow coolant flow — when it fails, it fails in one direction. P0128 is the common code for a thermostat stuck open. Replacement cost: $10 to $30 in parts DIY, $150 to $300 at a shop. A $15 part that prevents a $2,500 head gasket failure.
Bad Brake Pads — Symptoms and Replacement
Worn brake pads cause squealing when braking (wear indicators touching the rotor), grinding when braking (metal backing plate contacting the rotor), longer stopping distances, a soft or spongy pedal, and vibration through the pedal. Some pads have wear indicators that squeal at light braking pressure to warn you before the metal contacts the rotor. Once you hear grinding, the pads are gone and the rotor is being damaged. Replacement cost: $30 to $100 in parts per axle DIY, $150 to $350 at a shop. Replace pads when friction material reaches 3mm thickness — do not wait for grinding.
Symptoms of Bad Car Parts: Complete Guide to Identifying Failed Components
Common Component Failures
Bad alternator: dimming lights, battery warning, stalling. Bad fuel pump: no start, stalling, loss of power under load. Bad catalytic converter: rattling, sulfur smell, failed emissions. Bad wheel bearing: humming or grinding that increases with speed. Bad ignition coil: misfire, rough running, flashing check engine light.
Why Early Detection Matters
Recognizing symptoms of a failing part before it fails completely prevents breakdowns, expensive secondary damage, and unsafe driving conditions. Use the AI diagnosis tool with your specific symptoms for a ranked cause list.
Bad Spark Plugs — Symptoms and Replacement
Worn spark plugs cause rough idle, hesitation under acceleration, reduced fuel economy, hard starting, and a flashing or steady check engine light with misfire codes P0300 through P0308. Spark plugs fire thousands of times per minute — over tens of thousands of miles, the electrode erodes and the gap widens, weakening the spark. Symptoms appear gradually, so many drivers do not notice until fuel economy drops or a misfire code appears. Replacement cost: $20 to $60 in parts for a 4-cylinder engine DIY, $100 to $250 at a shop. Replace at the manufacturer interval: 30,000 miles for copper, 60,000 to 100,000 miles for iridium or platinum.
Bad Thermostat — Symptoms and Replacement
A stuck-open thermostat causes the engine to run cold, the temperature gauge to stay low, poor fuel economy, and the heater to blow lukewarm air. A stuck-closed thermostat causes rapid overheating, the temperature gauge to spike into the red, and steam from under the hood. The thermostat is a simple valve that opens at a specific temperature to allow coolant flow — when it fails, it fails in one direction. P0128 is the common code for a thermostat stuck open. Replacement cost: $10 to $30 in parts DIY, $150 to $300 at a shop. A $15 part that prevents a $2,500 head gasket failure.
Bad Brake Pads — Symptoms and Replacement
Worn brake pads cause squealing when braking (wear indicators touching the rotor), grinding when braking (metal backing plate contacting the rotor), longer stopping distances, a soft or spongy pedal, and vibration through the pedal. Some pads have wear indicators that squeal at light braking pressure to warn you before the metal contacts the rotor. Once you hear grinding, the pads are gone and the rotor is being damaged. Replacement cost: $30 to $100 in parts per axle DIY, $150 to $350 at a shop. Replace pads when friction material reaches 3mm thickness — do not wait for grinding.
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