P1391 Engine Trouble Code
What is P1391?
P1391 code can indicate a faulty oxygen sensor, which may eventually damage the catalytic converter (repair cost: $2,000–$2,200). Professional diagnosis costs around $200–$210. Oxygen sensors are often straightforward to replace — check your owner's manual for location and instructions. This issue should be addressed promptly to prevent further damage.
Code Information
| Code Type: | OBD-II Powertrain (P) Trouble Code |
| System: | Powertrain |
| Code: | P1391 |
P1391 Symptoms
Check Engine Light
Illuminated dashboard warning
Engine Stalling
Engine stops unexpectedly or misfires
Performance Issues
Reduced power or acceleration
Starting Problems
Difficulty starting the engine
P1391 Code Structure
Understanding what each digit means in the P1391 powertrain trouble code:
| P | 1 | 3 | 9 | 1 |
|---|---|---|---|---|
| Powertrain Code | Fuel And Air Metering | Throttle/Pedal Position Sensor/Switch A Circuit Intermittent | Crankshaft Position Sensor A Circuit Malfunction | Crankshaft Position Sensor A Circuit Low Input |
How to Fix P1391
Diagnostic Steps:
Regarding P1391, carefully inspect the wire harness near the intake manifold bracket, best accessed from below near the oil filter. Look for chafing, pinching, or damaged insulation.
Repair Solution:
Verify all electrical connections are clean and tight. Check for damaged wiring, especially in high-heat or high-vibration areas. Use manufacturer wiring diagrams for accurate diagnosis.
Technical Notes:
P1391 on electronically controlled automatic transmissions relates to shift solenoid operation. The solenoid actuates hydraulic circuits controlling clutches or bands for gear changes.
P1391 Description
P1391 OBD-II Trouble Code: Glow Plug Circuit Low Input Bank 1 is one of the definitions for the P1391; however your vehicles manufacturer may have a different definition for the P1391 code. Please check below for your specific
Main Cause
The primary reason for P1391 OBD-II Engine Trouble Code is: Throttle/Pedal Position Sensor/Switch A Circuit Intermittent.