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4.0L V8 S65•RWD•DCT•gas•S65B40
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P1085moderate severityPowertrain

Fuel Control Mixture Lean Bank 2

on 2010 BMW M3 E90 4.0L V8 S65 · RWD

What this code means

The DME detected a lean fuel mixture condition on Bank 2 beyond the correction capability of the long-term fuel trim. This often accompanies P1083 on V-configuration engines but can appear independently on Bank 2.

Symptoms

  • Check Engine Light
  • Rough idle
  • Lean misfire under load
  • Hesitation
  • Poor fuel economy

Common causes

  • Vacuum leak on Bank 2 intake side
  • Weak or clogged fuel injectors Bank 2
  • Low fuel pressure
  • Faulty MAF sensor
  • Intake manifold gasket leak Bank 2

Diagnostic steps

  1. Smoke test for vacuum leaks focusing on Bank 2
  2. Compare fuel trims Bank 1 vs Bank 2
  3. Test fuel pressure and volume
  4. Inspect intake manifold gasket
  5. Test individual injector flow rates

Repair notes

Repair vacuum leaks or fuel delivery issues on Bank 2 side.

Other Powertrain codes on this vehicle

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