981 · Fuel

P0171

System Too Lean (Bank 1)

MED SEVERITY

Long-term fuel trim on Bank 1 exceeded the lean threshold; the DME is adding maximum fuel to compensate.

SYMPTOMS

  • Check-engine light
  • Rough idle
  • Hesitation
  • Slight power loss

LIKELY CAUSES

  • Vacuum/intake leak
  • Dirty or failing MAF
  • Low fuel pressure
  • Weak fuel pump
  • Dirty injectors

DIAGNOSIS STEPS

  • Read fuel trims
  • Smoke-test the intake
  • Check MAF reading vs expected
  • Verify fuel pressure

RELATED PARTS

  • MAF sensor
  • Intake gaskets/boots
  • Fuel pump
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