P0171 🟡 Moyen ✅ Can drive (carefully)
System Too Lean — Bank 1
The ECU is constantly correcting a lean mixture (too much air, not enough fuel). If ignored, this can cause engine damage over time.
💷
Average repair cost
£9 — £220
🔍 Symptoms
- → Check engine light on
- → Rough idle
- → Hard cold starts
- → Slight power loss
- → Increased fuel consumption
⚙️ Common Causes
- 1Air intake leak (split hose, loose clamp)
- 2Dirty air filter
- 3Dirty or failing MAF sensor
- 4Failing fuel pressure regulator
- 5Clogged injectors
🔧 Recommended Fixes
- 1Clean MAF sensor with MAF cleaner spray (~£9)
- 2Replace air filter (~£8-20)
- 3Inspect all intake hoses for cracks
- 4Check fuel pressure
- 5Replace MAF sensor if cleaning fails (~£60-180)
🛒 Recommended Parts (Amazon UK)
MAF sensor cleaner spray~£9
View on Amazon UK →Car air filter~£8-20
View on Amazon UK →Fuel injector cleaner~£8
View on Amazon UK →Affiliate links — same price for you, we may earn a small commission.
Frequently Asked Questions
Can I clear this code without fixing it?
Yes, but it will return if the underlying issue isn't fixed. Clearing a code only tells you if the problem is permanent or intermittent.
Will this code fail an MOT?
Probably yes if the check engine light is on during the MOT. The MOT checks OBD readiness monitors since 2018.