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2005 RAM 3500
5.9L I6 Cummins•4WD•diesel•ISB•turbo
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Repairs0Labor523Torque138Fluid11DTC1684Battery1Maintenance0Recalls0
P0840moderate severityPowertrain

Transmission Fluid Pressure Sensor/Switch A Circuit

on 2005 Ram 3500 5.9L I6 Cummins · 4WD

What this code means

The PCM detected a problem in the transmission fluid pressure sensor or switch circuit A. This can cause incorrect line pressure readings and affect shift quality.

Symptoms

  • Harsh or erratic shifting
  • Transmission warning light on
  • Possible limp mode

Common causes

  • Faulty transmission fluid pressure sensor
  • Damaged wiring or connector
  • Low or dirty transmission fluid
  • Internal transmission pressure fault

Diagnostic steps

  1. Scan for codes and check freeze frame data
  2. Check transmission fluid level and condition
  3. Inspect sensor wiring and connector
  4. Test sensor resistance and compare to spec
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🔧 Database maintained under the daily editorial review of Chris Hackleman · Master Technician · 20+ years. Spot an error? Use the Help link above — a human reads every report.
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