Checking glow plugs is a crucial part of diesel engine maintenance. A faulty glow plug can lead to hard starting, rough idling, and reduced fuel efficiency. This guide will show you how to check your glow plugs using VCDS (Vag-Com Diagnostic System), a powerful diagnostic tool for Volkswagen, Audi, Seat, and Skoda vehicles.
VCDS allows you to access the engine control unit (ECU) and read diagnostic trouble codes (DTCs) related to glow plugs. It also enables you to perform output tests to activate each glow plug individually and verify its functionality. This is a much more effective method than visually inspecting glow plugs or using a test light.
Using VCDS for Glow Plug Diagnostics
Before you begin, ensure you have a genuine VCDS interface and the latest version of the software installed on your computer. Connect the interface to your vehicle’s OBD-II port and launch the VCDS software.
1. Accessing the Engine Control Module:
- Select “Select Control Module.”
- Choose “01 – Engine.”
2. Reading Fault Codes:
- Click on “Fault Codes – 02.”
- This will display any stored DTCs related to the glow plug system. Note down any codes present before clearing them. Common glow plug fault codes include:
- P0380 – Glow Plug/Heater Circuit ‘A’ Malfunction
- P0671 – Cylinder 1 Glow Plug Circuit
- P0672 – Cylinder 2 Glow Plug Circuit (and so on for each cylinder)
3. Performing Output Tests:
- Go to “Output Tests – 03.”
- In the list of available tests, locate the glow plug activation test. The exact name may vary depending on your vehicle model, but it will typically be something like “Glow Plug Activation” or “Glow Plug Test.”
- Select the test and follow the on-screen prompts. VCDS will activate each glow plug in sequence. Observe the measured values for each glow plug. A properly functioning glow plug should show a significant current draw. A low or zero current draw indicates a faulty glow plug.
4. Interpreting Results:
- If you find any fault codes or abnormal readings during the output test, you likely have a bad glow plug. Replace any faulty glow plugs with OEM-quality replacements.
- After replacing glow plugs, clear the fault codes and re-run the output test to verify the repair.
Additional Tips:
- Check the glow plug wiring harness for any damage or corrosion.
- Inspect the glow plug relay and fuse.
- Refer to your vehicle’s specific repair manual for detailed instructions and wiring diagrams.
By utilizing VCDS, you can accurately diagnose glow plug issues and ensure your diesel engine starts reliably in cold weather. This guide provides a general overview; consult your vehicle’s specific documentation for detailed procedures and safety precautions.
