P1278 Cylinder 8 High to Low Side Open (7.3L Diesel)

Category: Powertrain - Fuel/Air Metering
Severity: Check Engine Light
Applies to: F-250/F-350 Super Duty with 7.3L Power Stroke

What does P1278 mean on a Ford?

P1278 — Cylinder 8 High to Low Side Open (7.3L Diesel). This Ford-enhanced code applies to F-250/F-350 Super Duty with 7.3L Power Stroke.

Common causes of P1278

Open injector solenoid on cylinder 8
Broken harness wire (cylinder 8 runs hot behind the turbo)
Unplugged connector
Failed injector
IDM fault

How to fix P1278

Buzz test cylinder 8
Inspect the heat-exposed harness routing
Test injector resistance
Reseat connectors
Replace the injector or repair wiring