Poor fuel economy
MPG dropped? Avoid guessing — check trims, tyres, drag, sensors, and driving conditions.
MED RISK
Common symptoms
- MPG suddenly worse
- Fuel smell
- Sooty exhaust
- Rough running or hesitation
Cost expectations
DIY: £0–£60. Garage: £80–£300+.
Note: prices vary by car and region. Use this as a planning range.
Most likely causes (ranked)
- Tyre pressure/drag — Underinflation and binding brakes.
- Sensor bias — O2/MAF/MAP/coolant temp.
- Air/boost leak — ECU overfuels to compensate.
- Injector leak — Rich running and fuel dilution.
- DPF/EGR issues (diesel) — Frequent regens and soot increase fuel use.
Quick checks (fast, low-cost)
- Check tyre pressures and brake drag (hot wheel after short drive).
- Scan fuel trims and coolant temp readings.
- Inspect intake/boost hoses for leaks.
- Check for fuel smell and oil dilution.
- If diesel, check DPF regen frequency and soot load.
Recommended tools
These tools make diagnosis faster and stop you buying random parts.
Related fixes
If your symptoms don’t match perfectly, check these next.
What to do next
- Fix drag and basics first.
- Use trims to avoid random parts.
- If fuel dilution is present, address injector leak quickly.
AutoSolveHub helps you narrow possibilities. Always confirm critical repairs with proper testing and safe procedures.