P1399: Glow Plug Circuit High Side, High Input
MediumPowertrainDiesel System
What does P1399 mean?
P1399 is a diagnostic trouble code indicating "Glow Plug Circuit High Side, High Input". The ECU is detecting a voltage reading that is below the expected range in the diesel system circuit. This typically points to a wiring short, a faulty sensor, or a grounding issue.
Common causes
- Damaged or corroded wiring harness
- Loose or disconnected electrical connector
- Failed diesel system sensor or actuator
- Blown fuse in the related circuit
- Poor ground connection
What should you do?
Schedule a diagnostic appointment at your earliest convenience. The vehicle is generally safe to drive short distances, but the underlying issue should be addressed to prevent it from worsening.
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Code P1399 can mean different things depending on your vehicle. TorqueBot gives you a diagnosis specific to your make, model, and year.