What it means
The control module detects an intermittent fault in the transmission fluid pressure sensor/switch E circuit.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
Transmission fluid pressure sensor/switch E reports pressure information to the control module for transmission control. P0991 means the E circuit fault comes and goes, often when a loose connector or chafed harness makes contact intermittently, rather than remaining continuously high or low.
Common causes
Most likely first.
- Connector not seated
- Harness chafing intermittently
- Connector with intermittent contact under vibration
Symptoms
- Check engine or transmission warning light on
- Harsh, delayed, or missing shifts
- Possible limp mode (locked in one gear)
- Slipping or shuddering during gear changes
How to diagnose it
- Save freeze-frame data and review E sensor live data and code status to identify when the signal drops out or becomes erratic.
- Inspect the E sensor connector for incomplete seating, corrosion, fluid, or terminals that do not hold firmly.
- Trace the E sensor harness where it bends or contacts the transmission and nearby parts, looking for chafing or intermittent contact points.
- With a scan tool monitoring the E signal, gently move the connector and harness to see whether the reading or fault status changes.
- If movement does not reproduce the fault, test the E circuit and sensor under the manufacturer's specified conditions, including checks for intermittent open or high-resistance connections.
Common fixes
- Fully seat the E sensor connector and secure the harness routing.
- Clean or replace corroded, loose, or weak connector terminals.
- Repair chafed wiring or an intermittent break in the E circuit.
- Replace pressure sensor/switch E if its signal drops out during testing with a sound harness.
Can I keep driving?
If the fault causes sudden harsh shifts, slipping, or limp mode, avoid further driving except to reach a safe stopping place; an intermittent signal can make shift behavior unpredictable. If shifting remains normal, drive gently for a short distance to diagnosis and avoid towing.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.