Service function guideGlow Plug Testing

This guide provides a complete, professional procedure for testing diesel glow plugs and their control circuit on passenger cars and light commercial vehicles, written for working mechanics and experienced DIY owners who need a reliable diagnostic path. It explains how the glow plug system operates, when testing is required, and how to prepare the vehicle and yourself before any measurement is taken. The step-by-step procedure covers electrical tests at the plug, the harness, and the control module, with clear pass and fail criteria at each stage. After finishing, you will be able to isolate a failed glow plug, a damaged circuit, or a faulty control unit and confirm the repair with a post-test check.