What does P1390 mean on a Ford?

P1390. Octane Adjust Out of Self-Test Range. Applies to F-150, Mustang with octane adjust (premium fuel switch).

What causes P1390 on a Ford?

Octane switch left in the wrong position for the test Failed octane adjust switch Open switch circuit Corroded connector PCM input fault

How do I fix P1390 on a Ford?

Set the octane switch per the test procedure and re-run Test switch continuity in both positions Inspect the circuit and connector Verify the PCM sees the switch change Replace the switch if the input never changes

Code

P1390

Octane Adjust Out of Self-Test Range

Category: Powertrain - Computer and Auxiliary Controls
Severity: Check Engine Light
Applies to: F-150, Mustang with octane adjust (premium fuel switch)
Related: No single generic twin. See OBD Codes List

Findings, check these first

Octane switch left in the wrong position for the test
Failed octane adjust switch
Open switch circuit
Corroded connector
PCM input fault

Standard procedure

Set the octane switch per the test procedure and re-run
Test switch continuity in both positions
Inspect the circuit and connector
Verify the PCM sees the switch change
Replace the switch if the input never changes

Code lookup

Type a code above, or start from a symptom or a common code.

Press / to jump to the box. Ford-enhanced powertrain, body, chassis and network codes. Generic P0xxx codes live on OBD Codes List.

Sources and review

Review: qualified. Read the source limits below.

OBDII.pro: P1390 Ford definition
live reference page (obdii.pro)
Supports: Ford-family meaning for P1390: Octane Adjust Pin Out Of Self Test Range
Fetched directly. obdii.pro is a publisher independent of the engine-codes family.

Last updated 2026-09-06.

Report a correction for P1390. Include your vehicle, the issue and a source if you have one.