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How to Check the Functionality of Glow Plugs

Model: (Various brands) Various
Part: Glow plugs

Here’s a simple method to check the functionality of glow plugs: they are essentially resistors, so apply voltage to them. Their very low internal resistance allows a high current to flow, making them glow. If the internal filament breaks, it stops working, just like a blown bulb. Here’s how to check each one: remove the metal bar connecting them, so they are disconnected from each other. Take a bulb and connect one terminal to the positive battery terminal and the other to the glow plug terminal. If the bulb lights up for all, you can be 99% sure they are all functioning. This is also a good opportunity to clean them.

Updated on 11 July 2026 by ScegliAuto

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