What Does P1390 Mean?
The octane adjustment shorting bar circuit is open or the bar has been removed. This circuit allows technicians to adjust ignition timing for different fuel octane ratings via a jumper connection.
Common Causes
40%
Octane adjustment jumper removed or not installed
25%
Open circuit in octane adjustment wiring
20%
Corroded or damaged octane adjustment connector
10%
PCM internal octane sense circuit failure
5%
Improper PCM programming or calibration
Diagnostic Steps
1
Step 1: Locate octane adjustment connector (often near PCM or in engine bay wiring)
2
Step 2: Verify if shorting bar or jumper is present and properly installed per manufacturer specs
3
Step 3: Test continuity through shorting bar and verify proper connection
4
Step 4: Inspect connector terminals for corrosion, damage, or spread terminals
5
Step 5: Measure resistance at PCM octane sense terminal with jumper installed and removed
Estimated Repair Cost
$50 - $300
Parts + labor, varies by vehicle and location
The octane adjustment shorting bar circuit is open or the bar has been removed. This circuit allows technicians to adjust ignition timing for different fuel octane ratings via a jumper connection.
The most common cause of P1390 (Octane Adjust Shorting Bar Out or Circuit Open) is: Octane adjustment jumper removed or not installed
Typical repair costs for P1390 range from $50 to $300, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Generally safe to drive. May cause mild performance issues or spark knock if using fuel octane different than PCM expects. Typically informational only.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1390 to identify the root cause.
OBDHut Mobile App
Scan codes directly from your car with the OBDHut app.
Coming Soon
Quick Info
Category
Powertrain
System
Ignition Timing Control
Difficulty
Type
Manufacturer
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
