The P0851 code in your 2020 BMW 5 Series indicates the park/neutral switch input circuit is providing a lower voltage signal than expected. This affects the transmission's ability to accurately determine the selected gear position.
Understanding Low Circuit Voltage
The 5 Series uses a transmission range sensor to determine gear selection. A low voltage reading suggests the signal is being pulled down by a short to ground, high resistance, or sensor failure.
Common Causes of P0851
- Short to ground in switch circuit
- High resistance reducing voltage
- Switch internal failure
- Wiring damage
- Connector corrosion
- Ground connection issues
Symptoms of Low Circuit Voltage
- Incorrect gear position displayed
- Check engine light on
- Starting problems
- Backup camera not activating
- iDrive gear display errors
- Shift interlock issues
BMW iDrive Integration
The 5 Series displays gear position in the iDrive system and instrument cluster. Low circuit voltage can cause display errors even if the transmission functions normally.