MasterTuning Fault code dictionary (DTC)

P0171 — System too lean

Severity: Warning Can you drive? Yes, no known limitation Make: All makes (OBD-II standard)
MeaningMore air (or less fuel) is entering the engine than expected. On petrol engines it is almost always an unwanted air leak.
FamilyPowertrain (P)

Typical symptoms

Rough idle
Hesitation under acceleration
Engine warning light on
Slower starting

Common causes

Cracked intake pipe or leaking gasket
Faulty PCV valve or breather
Dirty injectors
Weak fuel pump or blocked filter
Aged lambda sensor

What to do

Find the leak with a smoke test: it is the quickest method and solves most cases. Replacing the lambda sensor before ruling out leaks is often wasted money.

Frequently asked questions

What does code P0171 mean?

System too lean. More air (or less fuel) is entering the engine than expected. On petrol engines it is almost always an unwanted air leak.

Can I keep driving with code P0171 active?

Yes, no known limitation

Common causes — P0171

Cracked intake pipe or leaking gasket Faulty PCV valve or breather Dirty injectors Weak fuel pump or blocked filter Aged lambda sensor

How do you fix code P0171?

Find the leak with a smoke test: it is the quickest method and solves most cases. Replacing the lambda sensor before ruling out leaks is often wasted money.

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