Transmission Fluid Pressure Sensor Circuit Intermittent
The P0991 code indicates an intermittent fault in the transmission fluid pressure sensor or its circuit. This sensor monitors hydraulic pressure inside the transmission and sends a signal to the powertrain control module (PCM). An intermittent signal can cause erratic shifting, slipping, or limp mode. Common causes include a faulty sensor, damaged wiring, poor electrical connections, or low transmission fluid.
01. Most Common Causes
- Faulty transmission fluid pressure sensor
- Damaged or corroded wiring/connectors
- Low or contaminated transmission fluid
- Intermittent electrical short or open circuit
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Erratic or harsh shifting
- Transmission slipping or delayed engagement
- Vehicle enters limp mode
03. Step-by-Step Diagnosis
Step 1: Scan for additional codes and record freeze frame data.
Step 2: Inspect transmission fluid level and condition; top off or replace if necessary.
Step 3: Visually check wiring and connectors for damage, corrosion, or loose connections.
Step 4: Test the pressure sensor and circuit using a multimeter per manufacturer specifications.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive with this code as it can lead to transmission damage or unsafe driving conditions. Have the vehicle inspected promptly.
How much does it cost to fix?▼
Repair costs typically range from $50 to $150 for diagnosis and sensor replacement, but may vary depending on labor rates and parts.