Check engine light
CEL on? Use codes + symptoms to avoid guessing. This guide helps you prioritise what’s urgent.
MED RISK
Common symptoms
- CEL on steady
- CEL flashing (urgent)
- Reduced power sometimes
- Rough running or none
Cost expectations
DIY: £0–£60. Garage: £80–£200+.
Note: prices vary by car and region. Use this as a planning range.
Most likely causes (ranked)
- Misfire — Flashing CEL; protect the catalytic converter.
- Emissions sensor fault — O2 sensor, evap leak, etc.
- Boost/air issue — Underboost/overboost, MAF/MAP.
- DPF/EGR (diesel) — Soot load and EGR codes.
- Cooling faults — Thermostat, temp sensors.
Quick checks (fast, low-cost)
- Scan codes and note freeze frame if available.
- If flashing, avoid hard driving and diagnose misfire first.
- Check for obvious issues (loose fuel cap for evap).
- Look for related symptoms and follow the matching fix guide.
- Clear codes only after recording them.
Recommended tools
These tools make diagnosis faster and stop you buying random parts.
What to do next
- Codes are clues — don’t clear them immediately.
- Flashing CEL is urgent.
- Use the Fix Library to narrow likely causes per symptom.
AutoSolveHub helps you narrow possibilities. Always confirm critical repairs with proper testing and safe procedures.