What is the car doing?
Start with shaking, overheating, warning lights, hard starting, low power, smoke, smell, or noise.
Browse symptoms →Troubleshooting
Identify the problem before replacing the part.
Start with what the vehicle is doing, check how urgent it is, then use evidence to narrow the cause.
Choose a starting point
Use the path that matches your situation
Can it still be driven?
Separate stop-now warnings from problems that need limited driving, prompt service, or monitoring.
Check urgency →How should I diagnose it?
Use observations, codes, freeze-frame data, and safe tests before buying a replacement part.
Follow the process →Safety first
Know when to stop driving safely
A flashing check-engine light, oil-pressure warning, severe overheating, heavy knocking, fuel leakage, or sudden loss of power needs immediate attention.
Open diagnostic tools →Stop safely
Protect people first, then prevent additional vehicle damage.
Limit driving
Arrange diagnosis when drivability or warning lights persist.
Inspect and monitor
Record when a mild symptom occurs and whether it changes.
Browse by symptom
Start with what the car is doing
A symptom is evidence—not a diagnosis. Choose the closest match for safe first checks and likely systems.
SYMPTOM GUIDE
Car shakes at idle
Separate a misfire, mount, air, fuel, or mechanical issue.
Open guide →SYMPTOM GUIDEEngine is overheating
Know when to stop and what not to open while hot.
Open guide →SYMPTOM GUIDEBattery light is on
Treat it as a charging-system warning, not a parts verdict.
Open guide →SYMPTOM GUIDECheck-engine light is flashing
Understand the misfire risk and immediate response.
Open guide →SYMPTOM GUIDEOil-pressure light is on
Stop safely and protect the engine from pressure loss.
Open guide →SYMPTOM GUIDETire-pressure light is on
Check cold pressure, damage, and TPMS behavior.
Open guide →Four-step workflow
Replace guesses with a repeatable process
Good diagnosis uses observations and tests to narrow the cause before money is spent on parts.
- 01
Notice
Record the warning light, sound, smell, weather, speed, and driving condition before anything changes.
- 02
Verify
Repeat only safe checks and inspect simple causes you can confirm without damaging the vehicle.
- 03
Scan
Read codes, freeze-frame data, and live values. Research the affected system—not only the code.
- 04
Decide
Choose the safest next step: monitor, test further, repair, book service, or stop driving.
COMMON MISTAKE
A code identifies a system—not automatically a failed part.
Save codes and freeze-frame data, then confirm wiring, connectors, air leaks, fuel delivery, related sensors, and live values before replacing anything.
Troubleshooting library
Continue with a reviewed answer
Browse practical guides for warning lights, OBD-II codes, overheating, idle vibration, and electrical problems.