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1997 SUBARU OUTBACK
2.5L H4•AWD•AUTOMATIC•gas
4 active safety recalls on this vehicle — view recalls
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Repairs0Labor546Torque3614Fluid8DTC633Battery1Maintenance0Recalls4
P0040moderate severityPowertrain

O2 Sensor Signals Swapped Bank 1 Sensor 1 / Bank 2 Sensor 1

on 1997 Subaru Outback 2.5L H4 · AWD

What this code means

The PCM has determined that the upstream O2 sensor signals for Bank 1 and Bank 2 are swapped, likely due to incorrect wiring after sensor replacement.

Symptoms

  • Check Engine Light
  • Poor fuel economy
  • Rough running
  • Failed emissions

Common causes

  • O2 sensor connectors swapped after service
  • Wiring crossed between banks
  • Incorrect sensor installation

Diagnostic steps

  1. Verify which O2 sensor is connected to which bank
  2. Trace wiring from each sensor to PCM connector
  3. Check for crossed connectors

Repair notes

Swap the sensor connectors to the correct banks.

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🔧 Database maintained under the daily editorial review of Chris Hackleman · Master Technician · 20+ years and Jeff Moore · Master Lexus & Toyota Mechanic · 20+ years. Spot an error? Use the Help link above — a human reads every report.
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