I was reading this question about an owner checking the alternator by disconnecting the battery, which is an easy way to validate on a gasoline engine. The single answer assumes that the OP is referring to a gasoline engine vehicle, but there is a diesel engine options for the vehicle.

It has been a while since I last played with any diesel engines, but they used to all have mechanically timed fuel injection, so once you get it running no electrical power is required to keep running.

Is this still the case? can you assume that all diesel engines don't require electricity to continue running, or do some now have electronically controlled fuel delivery that is dependent on an intact charging system?


2 Answers 2


Most modern diesel engines (ie: engines after mid-80s) require some electricity to run because they are electronically controlled. This is due to computers controlling the fuel charge and monitoring of the engine itself. Without this, the diesel engine has no control. They also require electricity to power the primary fuel pump, to move the fuel from the tank to secondary high pressure pump. (NOTE: A mechanical pump could be used in place of an electrically driven pump, but electric pumps are more common today.) Modern diesel engines can also utilize electronic injectors to meter the fuel being forced into the combustion chamber. So, while it is true, a diesel engine would not require electricity to run, the modern ones do utilize electricity peripherally to maintain better fuel economy and lower emissions.

  • 1
    Exactly: it's a difference between theoretically and practicality.
    – Bob Cross
    Mar 16, 2014 at 20:31
  • Out of curiosity, do modern diesels use electronic throttles as well? Jun 22, 2016 at 18:53
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    Yes, modern diesels do have an electronic throttle. Emission requirements have resulted in sensors and wires all over the place. Computer and expensive software are required for troubleshooting just about anything on an engine.
    – john D.
    Jun 23, 2016 at 1:04

disconnecting the battery with the engine running on ANY car with an alternator is a very bad idea - this can damage the alternator or other electronic components. It used to be done when dynamos were fitted and was not an issue. For diesels, those that were purely mechanical were obviously fine, but modern ones with electronic control no as above.


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