P27ED: mode-valve A position circuit voltage is too low

P27ED is the low-voltage circuit diagnosis for mode-valve A position feedback. The cited internal ETRS strategy fails when raw sensor voltage falls below 0.414 V. It describes either a ground short or an open circuit as possible electrical interpretations.

Low does not uniquely mean grounded

The source's inclusion of an open circuit matters. A low input alone cannot distinguish an unintended ground connection from a lost circuit path, and it does not prove the position sensor itself must be replaced. The exact circuit architecture and test procedure are needed to separate those possibilities.

Monitoring requires internal ETRS configuration, calibration enablement and battery voltage above 9 V for more than one second. The condition must be present for 0.100 seconds within a 0.163-second window, updated at 6.25 ms. Reporting is Type A, one trip.

Verification

Preserve the raw sensor voltage and range-control status. The driver's requested range is not a substitute for electrical feedback validity, and successful movement on one attempt does not independently establish an intermittent circuit is sound.

After the identified cause is addressed, confirm the enabled low-range circuit check completes successfully. Range and park functions can affect unintended vehicle movement, so follow the manufacturer's professional testing and securing procedures. This summary provides no terminal pinout or authority to bypass range-control protections.

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 2284.