The Function of Glow Plugs:
The function of glow plugs in order for a diesel engine to reliably start at low outside temperatures and run with low noise and low emissions during the warm-up phase, glow plugs are fitted which protrude into the cylinder. The glow plugs must very quickly make a high temperature available to assist the ignition process, subsequently maintaining this temperature regardless of boundary conditions or even adapting it to suit them.
So, can you drive securely by the Glow Plug Light on? It depends on the nature of the problem. Occasionally, when the Glow Plug Light comes on, the engine in your car will go into "safety" mode, in order to stop any damage to the engine. If this should occur, you might perceive a drop in performance. This is likely not a big deal if you're just booting around town, but it could present a safety issue if it occurs when you are performing a maneuver like passing or merging on the highway. Here is what you need to do.
1. Get a diagnostic check as soon as possible in order to find out just what the problem is and how to correct it. You don't want to leave this to guesswork. A great deal of the time, the problem can be credited to faulty crank sensors or cams, but there is also other equipment that can cause the Glow Plug Light to come on.
2. If you must carry on to drive, make sure to take it easy. It would almost certainly be best to avoid highway driving.
3. Do not assume that the problem will just go away on its own it won't. The Glow Plug Light came on for a cause, and until you find out what that motive is and have it corrected, it is going to wait on.
4. You can probably drive safely with the Glow Plug Light on as long as you take it easy. But you do need to get it checked out. Always remember, your warning lights are trying to tell you something