Glow plugs help your car to start when it is dead cold out. But the engine seems to start just fine in the Bay Area even after glow plug failure. Sometimes customers are confused about what glow plugs actually do, and why the engine really needs them. Glow plugs are tiny electrical heaters that screw into the cylinder head until the tips protrude slightly into the combustion chambers. Glow plugs are needed to start the engine below 50 degrees. But they also turn on any time you accelerate and the mixture goes a bit rich. Then they glow to help reduce emissions. And that also explains the fairly high frequency of glow plug failure in the Tdi cars up through 2003, The glow plugs spend a fair amount of time turned on, especially if one drives briskly. It also explains why the harnesses fail, as the wires are a bit small for the job. Most glow plug failure occurs somewhere before 100,000 mile in engines made up through 2005. The later CR diesels since 2009, including the VW Jetta, Passat and Touareg, and the Audi A3, A6, Q5 and Q7, have had no real history of glow plug failure to date.
Glow plug failure diagnosis is fairly easy. Most problems take less than an hour to sort out. Maybe 25% of the jobs get more complicated than just replacing the glow plugs. Replacing the glow plugs is a quick job in a 4 cylinder Tdi, not so quick in a 6 cylinder, and half a day in a 10 cylinder Touareg Tdi. The electrical harness on the engine for the flow plugs may need to be tested. We find a small percentage of those harnesses need to be replaced as well. Installing glow plugs is not for amateurs. The threads are fine and the metal is soft, so exact torque is mandatory when tightening them. And it is easy to damage the electrical harness when pulling it off. If your warning light comes on, call your Service Advisor. Get some good advice.
Quick Clue: NEVER use starting fluid in a modern diesel motor. The most common result is that it can shatter glow plugs and even break piston rings. If your diesel won’t start, fix it. Do not risk destroying it.