Complete Car Diagnostic Guide: Professional Troubleshooting Handbook
Step-by-step instructions to diagnose and fix common car problems like a professional mechanic
Quick Navigation
⚡ Electrical System Diagnostics
Battery Not Charging
- Dim headlights and interior lights
- Battery warning light illuminated
- Difficulty starting engine
- Electrical components malfunctioning
Diagnostic Steps:
Voltage Test: Check battery voltage with engine off (should be 12.4-12.7V) and with engine running (should be 13.7-14.7V)
Visual Inspection: Check for corroded terminals, loose connections, or damaged wiring
Alternator Test: Measure alternator output and check drive belt tension
🔧 Engine Performance Diagnostics
Engine Misfire
- Rough idle and vibration
- Loss of power and acceleration
- Check engine light flashing
- Poor fuel economy
Diagnostic Steps:
Code Reading: Read diagnostic trouble codes with OBD2 scanner
Spark Plug Inspection: Check spark plugs for wear, fouling, or damage
Compression Test: Perform cylinder compression test to identify mechanical issues
📟 Common OBD2 Error Codes
| Code | Description | Possible Causes |
|---|---|---|
| P0300 | Random/Multiple Cylinder Misfire | Spark plugs, ignition coils, fuel injectors |
| P0420 | Catalyst System Efficiency Below Threshold | Catalytic converter, oxygen sensors |
| P0171 | System Too Lean (Bank 1) | Vacuum leaks, MAF sensor, fuel pressure |
🚨 Emergency Troubleshooting Tips
If Your Car Won’t Start:
Check battery connections for corrosion and tightness
Listen for clicking sound (indicates starter issue)
Check fuel gauge and ensure there’s adequate fuel
Try jump-starting if battery is dead