What does it mean?
OBD II fault code P0380 is a generic code that is defined as “Glow plugs, circuit A –malfunction”, and is set when the PCM (Powertrain Control Module) detects a general malfunction or failure in the glow plug control circuit on a diesel powered application. Note that while “Circuit A” refers to a particular part or section of the glow plug control circuit, car manufacturers do not always number circuits or parts of circuits in the same way.
For this reason, it is important to refer to the manual for the affected application to determine which part of the glow plug control circuit is labelled “A” on that application. Failure to do this could result in a misdiagnosis, and the unnecessary replacement of parts and components. The purpose of glow plugs on diesel engines is to provide a source of intense heat to assist in the combustion process of the air/fuel mixture when the engine is cold, or below a minimum threshold temperature.
Typically, the glow plug control circuit consists of the- battery the ignition switch one or more relays one or more fuses and/or fusible links a dedicated engine coolant sensor wiring and connectors warning and/or indicator lights to indicate the status of the glow plug control circuit the glow plugs themselves Depending on the application, the circuit could also include a timer, or on most modern applications, a dedicated, stand-alone glow plug control module.
During normal operation of a diesel engine, combustion of the air/fuel mixture is accomplished by heating the mixture adiabatically, i.e., by heating the mixture through compression when the pistons are moving upwards during their compression strokes, and provided that the engine and all the components of the fuel injection system are both in good mechanical condition, the air/fuel mixture will combust completely.
Note though that the high speed at which the pistons move upward during the compression stroke greatly assists in heating the air/fuel mixture when the engine is running. However, at low ambient temperatures, it can be very difficult to ignite a diesel fuel/air mixture at start up because not only is combustion less efficient at low temperatures, but also because the air fuel mixture may not be compressed sufficiently to initiate combustion at engine cranking speeds.
Thus, to eliminate these problems, diesel engines use electrically heated glow plugs to provide a source of heat in the pre-combustion chamber of each cylinder to assist in igniting the air/fuel mixture at the compression peak. In terms of operation, glow plug control starts when the ignition is turned on.
At this point, the PCM receives input data on the engine coolant temperature (from a dedicated coolant temperature sensor), which on most applications, has to be below about 104 0 F (40 0 C) for the glow plug circuit to be activated. If the PCM determines that the engine coolant is below a pre-defined minimum threshold, it will feed power to a timer on some older applications, which in turn, will feed battery power to the glow plugs via a dedicated relay.
NOTE: On some older, non-monorail injection applications that still use glow-plug timers, the glow plugs will be fed battery power only for a predetermined time, (or until the engine coolant reaches a predetermined minimum temperature), which usually sufficed to get a cold engine running smoothly.
However, on monorail injection systems where the fuel injectors are controlled electronically, the PCM may adapt both the injection timing and the injection pulse width during the time the glow plug control circuit is in operation, which is usually until the engine coolant reaches a predetermined temperature before the glow plug control circuit is deactivated to remove power from the glow plugs.
It must be noted however, that regardless of the ambient temperature, the glow plug control circuit will not be activated if the engine coolant temperature exceeds a predefined minimum threshold. This is to both extend the life of the