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1998 BMW 328IS E36
2.8L I6 M52•RWD•AUTOMATIC•gas
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Repairs0Labor494Torque2174Fluid8DTC1210Battery1Maintenance0Recalls0
P0171high severityPowertrain

System Too Lean Bank 1

on 1998 BMW 328is E36 2.8L I6 M52 · RWD

What this code means

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

  1. Check fuel trim values at idle and 2500 RPM
  2. Perform smoke test for vacuum leaks
  3. Test fuel pressure at idle and under load
  4. Clean or test MAF sensor
  5. Check for exhaust leaks near manifold
  6. Check PCV system

Repair notes

Most common: vacuum leak. Perform smoke test first. Check MAF sensor. Test fuel pressure.

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