P0840 Buick Transmission Fluid Pressure Sensor A

P0841 Buick LR Pressure Switch Rationality Fault

Possible causes
– Transmission Solenoid/Pressure Switch harness is open or shorted
– Transmission Solenoid/Pressure Switch circuit poor electrical connection
– Faulty Transmission Solenoid/Pressure Switch
– Internal transmission damage
– Faulty Engine Control Module (ECM)
– Faulty Transmission Control Module (TCM)
Symptoms
– Engine Light ON (or Service Engine Soon Warning Light)
– Transmission will not shift gears.
P0841 Buick Description

Low/Reverse (LR).

The Transmission Control Module (TCM) has detected a pressure switch open or closed at an incorrect time.

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