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2021 HONDA CIVIC
1.5L I4 Turbo•FWD•CVT•gas•turbo
4 active safety recalls on this vehicle — view recalls
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Repairs403Labor504Torque3392Fluid7DTC1173Battery1Maintenance0Recalls4
P1751high severityPowertrain

Mainshaft Speed Sensor Circuit Malfunction

on 2021 Honda Civic 1.5L I4 Turbo · FWD

What this code means

The transmission mainshaft speed sensor is sending a faulty or missing signal to the PCM. This affects shift timing and gear selection accuracy.

Symptoms

  • Harsh or erratic shifting
  • Check engine light on
  • Transmission slipping

Common causes

  • Faulty mainshaft speed sensor
  • Damaged sensor wiring or connector
  • Metal debris on sensor tip
  • Faulty PCM

Diagnostic steps

  1. Scan for stored codes and freeze frame
  2. Inspect sensor connector and wiring
  3. Test sensor resistance and signal output
  4. Replace sensor if out of spec
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🔧 Database maintained under the daily editorial review of Chris Hackleman · Master Technician · 20+ years and Jeff Moore · Master Mechanic · 20+ years. Spot an error? Use the Help link above — a human reads every report.
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