Code Definition

P0840 — Transmission fluid pressure switch signal out of range - Circuit A

System: Powertrain  |  Type: Generic (OBD-II Standard)  |  Make: Generic

About P0840

P0840 is a generic (obd-ii standard) powertrain diagnostic trouble code. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P0840 is stored, the module has detected a plausibility fault — the measured value is in the electrical range but is not consistent with expected operating behaviour.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

Because P0840 is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

The P0840 fault code is set when the control module identifies an issue with the signal from the Transmission Fluid Pressure Switch in Circuit 'A.' This switch monitors the hydraulic pressure of the transmission fluid in various gears. The code is triggered when the signal from this pressure switch falls outside the expected range, either too high or too low. This could indicate a problem with the switch itself, the transmission fluid pressure, or the circuitry involved in transmitting the signal.

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