What Does P0380 Code Mean?

OBD-II Code P0380 is defined as a Glow Plug/Heater Circuit "A" Malfunction

The purpose of the Glow Plugs on a diesel engine is to heat up the combustion chambers to enable a quicker cold start. If the engine is already hot, the Glow Plugs aren't needed and will not 'light off'.

Code P0380 sets when the Power Train Control Module or PCM see less than 4 volts output to the Glow Plugs when the Glow Plugs should be energized or above 4 volts to the Glow Plugs when the Glow Plugs should NOT be energized.

P0380 Symptoms

  • Check Engine Light will illuminate
  • Failure of Emissions Inspections due to MIL malfunction
  • Vehicle may be hard to start
  • In rare cases, there are no adverse conditions noticed by the driver

Common Problems That Trigger the P0380 Code

  • Malfunction of the Glow Plug Relay
  • Malfunction of the GLow Plug Control Unit
  • Defective Glow Plugs
  • Defective wiring/connections in the Glow Plug wiring harness

Common Misdiagnoses

  • Glow plugs are replaced when the root cause is a defective Glow Plug Control Unit
  • Glow plugs are replaced when the root cause is a defective Glow Plug Relay
  • Glow plugs are replaced when the root cause is a defective wiring harness

P0380 Diagnostic Theory for Shops and Technicians

When inspecting for the cause of a Glow Pug circuit malfunction, I start by looking at the freeze frame data to get a picture of when the malfunction occurred. Then I use a data streaming scan tool and and zero in on the output voltage to the Glow Plugs. I'm looking for over 4 volts going to out to the Glow Plugs when I activate the Glow Plug warm up system. If there isn't, I locate the Glow Plug relay and test its function and its wiring harness. On systems where the Glow Plug relay isn't accessible, you have to test the Glow Plug Control Unit itself. Make sure the power and ground circuits going into and out of the Control unit have acceptable voltage drops. I look for .1-.2 volts (or less) on the ground side and .3-.5 volts (or less) on the positive side. I also check the Glow Plug harness for continuity by using a test light tethered to B+. I need to see bright illumination when I touch each of the Glow Plug harness connectors. This shows that the Glow Plugs and their wiring have solid continuity.

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