P1138 — Volkswagen — Long Term Fuel Trim Add Fuel Bank 2 System Too Lean

P1138 (Volkswagen): Long Term Fuel Trim Add Fuel Bank 2 System Too Lean — what it means, the affected system and what to check before replacing parts.

Meaning, symptoms, causes and checks

Long Term Fuel Trim Add Fuel Bank 2 System Too Lean. Source catalogue definition; confirm applicability using vehicle service information.

Affected system: Powertrain

Symptoms

  • Check Engine light illumination
  • Noticeable engine hesitation or misfire
  • Reduced engine power and performance
  • Decreased fuel economy
  • Rough engine idling

Possible causes

  • Vacuum leaks in the intake system
  • Faulty mass air flow (MAF) sensor
  • Clogged or leaking fuel injectors
  • Low fuel pressure or failing fuel pump
  • Exhaust leaks upstream of the bank 2 oxygen sensor

What to check

  • Inspect the intake manifold and vacuum lines for visible leaks
  • Measure the fuel system pressure to ensure it meets factory specifications
  • Examine the bank 2 oxygen sensor wiring harness for damage or corrosion
  • Clean or replace the mass air flow sensor if readings are erratic
  • Test individual fuel injectors for proper spray pattern and flow rate