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P0380 Severity
Identifying an OBD code is just the start of a complete diagnostic routine. Most trouble codes are caused by a sensor reporting a value that is out of range. Just replacing a sensor may not fix underlying issues. Be sure to understand the code, the part or system in your car that the code refers to, and the risks of delaying professional repair.
Proper diagnosis will save you time and money on unnecessary repairs.
Urgent codes indicate immediate action is necessary. These are urgent and significant malfunctions that can cause severe damage to the vehicle or harm the driver and passengers.
Diesel engines use Glow Plugs to heat up the combustion chambers to enable a quicker cold start. If one or more glow plugs is not working properly, the engine control module (PCM) will set code P0380.
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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.
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.