P1527 on a GM vehicle means the transmission control module (TCM) has compared the hydraulic pressure switch states inside the transmission against the gear range it commanded and found a mismatch. The TCM expects a specific pattern of pressure switch signals for the selected range, and one or more switches report a state that does not agree with that expectation.
Guidance is general and written for GM vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.
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