P0991 Transmission Fluid Pressure Sensor/Switch E Circuit Intermittent

P0991 indicates an intermittent transmission fluid pressure sensor or switch E circuit fault. The pressure signal drops out or becomes implausible only at times.

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 clear intermittent pressure-sensor faults without heat, vibration, and connector checks.

Symptoms of P0991

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 P0991

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

Monitor pressure sensor E data while repeating freeze-frame speed, load, temperature, and shift conditions.
Inspect internal harness movement, case connector terminals, sensor connector fit, fluid intrusion, and wiring strain.
Check whether ratio, shift, or pressure-control codes appear at the same time as the pressure-signal dropout.

Related OBD-II codes

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