Frayed, chafed, or intermittently shorting wiring in the sensor 'E' circuit; Loose or corroded electrical connector at the sensor or transmission case; Failing transmission fluid pressure sensor or switch 'E' itself; Internal transmission harness damage from heat or fluid contamination; Poor ground connection for the transmission control module or sensor return circuit; Low or degraded transmission fluid causing erratic pressure readings

DTC codes / P09xx · Transmission / P0991

P0991Transmission Fluid Pressure Sensor/Switch 'E' Circuit Intermittent

P0991 indicates that the transmission control module has detected an intermittent fault in the electrical circuit for transmission fluid pressure sensor or switch 'E'. The circuit works correctly at times but momentarily drops out or sends erratic signals, which the computer flags as a pending or stored code.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaTransmission

Symptoms you may notice

Illumination of the check engine light or transmission warning light
Often no symptoms besides the warning light, especially if the fault is brief
Harsh or delayed gear shifts during certain driving conditions
Transmission may enter limp mode (stuck in one gear) intermittently
Slight shudder or slip when the pressure signal drops out momentarily

Common causes, most likely first

Frayed, chafed, or intermittently shorting wiring in the sensor 'E' circuit
Loose or corroded electrical connector at the sensor or transmission case
Failing transmission fluid pressure sensor or switch 'E' itself
Internal transmission harness damage from heat or fluid contamination
Poor ground connection for the transmission control module or sensor return circuit
Low or degraded transmission fluid causing erratic pressure readings

How to diagnose and fix it

Check transmission fluid level and condition; top off or service if contaminated
Inspect the sensor 'E' connector and wiring for looseness, corrosion, or chafing
Wiggle-test the harness while monitoring live pressure data to reproduce the intermittent fault
Measure resistance and voltage on the sensor 'E' circuit and compare to manufacturer specifications
Replace the transmission fluid pressure sensor or switch 'E' if electrical tests point to it
Repair or replace damaged sections of the transmission wiring harness
Clear the code and perform a road test to confirm the repair and ensure no pending code returns

Intermittent faults that fool many technicians

A sensor that tests perfectly on a cold engine can still fail when hot, so always reproduce the fault with the transmission at operating temperature.
The code often sets from a momentary voltage spike or drop that lasts less than a second, making a simple multimeter check useless without a graphing scan tool.
A poor ground for the transmission control module can mimic a failed sensor 'E' and cause this code along with other unrelated transmission codes.
Aftermarket transmission fluid that is not the specified type can alter pressure sensor readings and trigger intermittent codes without any electrical fault.
Do not replace the sensor 'E' based solely on this code; always verify the circuit integrity first because wiring faults are more common than sensor failure.

Can I keep driving with P0991?

You can usually continue driving if the vehicle shifts normally, but avoid heavy towing or aggressive acceleration until the fault is repaired. If the transmission enters limp mode or shifts harshly, have it diagnosed promptly to prevent further damage.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.