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P0840 Powertrain

Transmission Fluid Pressure Sensor/Switch A Circuit Range/Performance

The transmission fluid pressure sensor A reading is implausible compared to commanded line pressure. The TCM detects sensor drift or hydraulic leakage.

Affected components

  • Transmission fluid pressure sensor
  • Valve body
  • Transmission pump

Common causes

  • High likelihood: Pressure sensor drift
  • Medium likelihood: Internal hydraulic leak
  • Low likelihood: Sensor element aged beyond calibration window

Possible symptoms

  • Check engine or transmission warning light on
  • Harsh, delayed, or missing shifts
  • Possible limp mode (locked in one gear)
  • Slipping or shuddering during gear changes

Diagnostic notes

  • The malfunction indicator lamp may illuminate

Related codes

Sources

Diagnostic information is provided for reference only. Confirm the code with a compatible scan tool and follow the vehicle manufacturer's service procedures before replacing components.

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