System Too Lean Bank 1
1999-2000 BMW 528iT E39 2.8L I6 🇨🇦
Description
The long-term fuel trim for Bank 1 has exceeded the positive limit, indicating the engine is running lean. The PCM is adding more fuel than normal to compensate.
Symptoms
- Check Engine Light
- Rough idle
- Hesitation on acceleration
- Poor fuel economy
- Possible misfires
- Hissing sound from vacuum leak
Common Causes
- Vacuum leak (intake manifold gasket, brake booster hose, PCV valve)
- Low fuel pressure
- Dirty or faulty MAF sensor
- Exhaust leak before O2 sensor
- Faulty O2 sensor
- Clogged fuel injector
Diagnostic Steps
- Check fuel trim values at idle and 2500 RPM
- Perform smoke test for vacuum leaks
- Test fuel pressure at idle and under load
- Clean or test MAF sensor
- Check for exhaust leaks near manifold
- Check PCV system
Repair Notes
Most common: vacuum leak. Perform smoke test first. Check MAF sensor. Test fuel pressure.
Related Codes
Other Powertrain Codes
- P0001Fuel Volume Regulator Control Circuit/Open
- P0002Fuel Volume Regulator Control Circuit Range/Performance
- P0003Fuel Volume Regulator Control Circuit Low
- P0004Fuel Volume Regulator Control Circuit High
- P0010Intake Camshaft Position Actuator Circuit/Open Bank 1
- P0011Intake Camshaft Position Timing Over-Advanced Bank 1
- P0012Intake Camshaft Position Timing Over-Retarded Bank 1
- P0013Exhaust Camshaft Position Actuator Circuit/Open Bank 1
- P0014Exhaust Camshaft Position Timing Over-Advanced Bank 1
- P0015Exhaust Camshaft Position Timing Over-Retarded Bank 1
P0171 on Other Vehicles
Common Questions
What does code P0171 mean on a 1999-2000 BMW 528iT E39?
P0171 stands for "System Too Lean Bank 1". The long-term fuel trim for Bank 1 has exceeded the positive limit, indicating the engine is running lean. The PCM is adding more fuel than normal to compensate.
What are the symptoms of P0171 on a BMW 528iT E39?
Common symptoms of P0171 include: Check Engine Light, Rough idle, Hesitation on acceleration, Poor fuel economy, Possible misfires, Hissing sound from vacuum leak.
What causes P0171 on a 1999-2000 BMW 528iT E39?
Common causes of P0171 include: Vacuum leak (intake manifold gasket, brake booster hose, PCV valve), Low fuel pressure, Dirty or faulty MAF sensor, Exhaust leak before O2 sensor, Faulty O2 sensor, Clogged fuel injector.