P0999 Shift Solenoid F Control Circuit High

P0999 indicates a high shift solenoid F control circuit signal. The control path is higher than expected or stuck high.

Code details

Generic OBD-II · P0

System: Transmission
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not condemn the controller before checking solenoid F wiring, connector, and internal harness integrity.

Symptoms of P0999

Harsh, delayed, or slipping shifts, or being stuck in one gear.
Check-engine light, sometimes with limp-home mode.
Flaring RPM or a shudder under load.

Common causes of P0999

Low or degraded transmission fluid.
A failing speed sensor, shift solenoid, or pressure-control circuit.
Wiring, connector, or internal hydraulic/mechanical faults.

Useful checks before replacing parts

Check for short-to-voltage, open ground, poor connector contact, and solenoid F control circuit faults.
Compare solenoid command with actual circuit voltage or current and gear-ratio response.
Inspect transmission connector sealing, internal harness routing, and recent wiring repairs.

Related OBD-II codes

These nearby transmission entries can help compare wording and pin down the fault area.