Glow plug indicator
A yellow light on diesel vehicles that shows the glow plugs are heating before the engine starts.
How to read it
UN Regulation No. 121 lists a diesel pre-heat tell-tale and sets it as yellow. In Ford's diesel F-150, the light is called the wait to start indicator: it comes on when the ignition is switched on, as part of the pre-start system, and Ford's manual says to wait until it goes out before starting the engine.
Also searched as: diesel coil light.
Dashboard symbols vary by manufacturer. The vehicle's owner's manual or a qualified mechanic can say what a light means for a particular vehicle.
What the glow plugs do
Ford's manual explains that as soon as the ignition is switched on, the glow plug control module energizes the glow plugs, and that they may stay on for a while after the engine has started, once the light is out.
More dashboard warning lights
Sources
- 2020 F-150 Owner's Manual, Ford Motor Company, Instrument Cluster: Wait To Start; Diesel Engine Fast Start Glow Plug System
- Regulation No. 121: Uniform provisions concerning the approval of vehicles with regard to the location and identification of hand controls, tell-tales and indicators, UN Regulation No. 121, United Nations Economic Commission for Europe (text published by Japan's Ministry of Land, Infrastructure, Transport and Tourism), Table 1
Last reviewed September 26, 2026 by Rory Hansen. How we research