P27EE: mode-valve A position signal exceeds its electrical limit

P27EE monitors a short-to-voltage condition on mode-valve A position feedback. The GM threshold is raw sensor voltage above 2.538 V. It applies to the internal electronic transmission range-control configuration described in the source.

A circuit result, not attained range

The high electrical signal does not by itself tell the technician that the transmission is physically in drive, reverse or park. Commanded range, attained mechanism state and electrical validity are separate observations. The source uses this code specifically to establish an invalid high input.

Battery voltage must remain above 9 V for more than one second and the monitor must be enabled. Failure is assessed for 0.100 seconds within a 0.163-second sample window at a 6.25 ms update rate. The entry is Type A, one trip.

Useful follow-up

Compare the raw sensor measurement with the correct circuit definition, and evaluate supply or signal faults through the prescribed service procedure. Do not substitute a generic five-volt sensor assumption for the actual 2.538 V diagnostic boundary.

Verification requires a completed upper-range check under qualified conditions. A dashboard selector indication alone cannot establish feedback integrity. Because this circuit supports range and park operation, secure the vehicle and use appropriate professional methods; the summary does not provide bypass, pin-probing or component-replacement instructions.

Source and application limits

This explanation covers the cited 2025 GM monitor. Confirm the vehicle and calibration in its service information before applying these limits; inclusion in this file does not establish model compatibility. GM diagnostic parameters, PDF page 2285.