The TDI is a diesel version of Volkswagen's best selling car in America, the Jetta. The combustion efficiency of a diesel engine is greatly reduced when the engine is cold, so glow plugs heat the engine block and cylinders before the engine starts. When the key is turned, a message warns the driver "wait to start" while the glow plugs heat up; then a few seconds later, a "start" notification will appear. Glow plugs wear out over time, but replacing them is a straightforward task that will save money at the auto repair shop.
Raise the hood and remove the bolts that secure the plastic engine cover with a socket wrench. Under the cover is the glow plug harness, a black rubber tube with four caps attached to the glow plugs.
Snap the glow plug harness off the glow plugs with your fingers. Set the harness to the side to access the glow plugs.
Attach an extension and a deep plug socket to a socket wrench. Push the socket over the glow plug and turn the wrench counterclockwise to remove it. Remove all four plugs in this manner.
Screw in each new glow plug into its respective hole in the cylinders by hand. Tighten each plug with the socket wrench.
Replace the glow plug harness and snap the caps onto the top of each glow plug. Replace the engine cover and tighten its retaining bolts.
Close the hood. Turn the key in the ignition and start the engine to test the glow plugs.
