Bank 1 mixture is consistently lean. Air leaks, MAF, low fuel pressure, or injector issues are common causes.

Can I drive with P0171?

Short trips at light load are okay. Delaying diagnosis can damage the catalyst and sensors; get it fixed soon.

What if P0171 and P0174 appear together?

Both banks show lean mixture. Shared causes (fuel pressure, filter, MAF) are common; single-sided air leaks are rarer.

P0171 OBD2 Error Code: System Too Lean (Bank 1)

Category: Engine and air-fuel · Last updated: February 1, 2026

What does this error code mean?

System Too Lean (Bank 1)

Common symptoms

Check engine light (MIL) on
Rough idle or hesitation during acceleration
Increased fuel consumption or loss of power
Engine enriches mixture but remains lean

What causes it?

Air leak in intake manifold, vacuum hoses, or gaskets
Dirty, damaged, or faulty mass air flow (MAF) sensor
Low fuel pressure, weak fuel pump, or clogged filter
Clogged or dirty fuel injectors
Exhaust leak (especially before oxygen sensor)

How to fix

Check intake and vacuum system for air leaks; repair gasket, hose, or manifold if needed
Clean or replace MAF sensor
Check fuel pressure and filter; replace pump or filter if faulty
Clean or replace injectors

Is it safe to drive?

Short trips at low load are acceptable. Extended lean running can damage the catalyst and oxygen sensors, affecting performance and emissions. Avoid long journeys, heavy loads, or high revs. Have it diagnosed and repaired as soon as possible.

Estimated repair cost

Estimated cost range (labour and parts): $15 – $100 USD. Costs vary by cause; simple MAF cleaning or gasket replacement 500–1500 TL; fuel pump or injector work 2000–3500 TL range.

Expert opinion

Check air filter, vacuum hoses, and intake gaskets first. Then monitor MAF and oxygen sensors with live data. Air leaks or dirty MAF are common causes; cleaning or gasket replacement often fixes it. Fuel pressure and injector balance should also be checked. Do not ignore the code—the underlying cause must be fixed.

For information only. Content on this site is for general guidance; it does not replace professional diagnosis or repair. Always consult a qualified technician before making decisions about your vehicle.

Frequently asked questions

What causes P0171?: Bank 1 mixture is consistently lean. Air leaks, MAF, low fuel pressure, or injector issues are common causes.
Can I drive with P0171?: Short trips at light load are okay. Delaying diagnosis can damage the catalyst and sensors; get it fixed soon.
What if P0171 and P0174 appear together?: Both banks show lean mixture. Shared causes (fuel pressure, filter, MAF) are common; single-sided air leaks are rarer.