2022 Mercedes-Benz Sprinter 3500 Glow Plug Replacement Cost

Driving a vehicle with a bad glow plug should be fine. In fact, when only one glow plug fails, the engine should run normally once near-operating temperatures are reached, given the engine can start. Diesels with block heaters may be easier to start, but the vehicle will exhaust smoke as the engine warms up. If the vehicle will not start, the glow plug must be replaced before driving. The engine may have extreme drivability issues and misfires until it has been completely warmed for several minutes. If there is a faulty glow plug causing a misfire at idle, the vehicle should not be driven until the engine has warmed thoroughly. Continued use in this condition will cause emissions component failure and carbon build-up in one or more cylinders, which can lead to hot-spotting, and detonation knocking after the engine is turned off.

Glow plugs are normal maintenance items for most vehicles, and the service schedule is listed in the owner's manual. If the glow plugs are leaking combustion gases, weak, or fail before the specified mileage, they should be replaced early, and inspected for defects.

Diagnosing a glow plug is most easily done with a computer scanning tool. The OBD code set for the glow plugs indicates that at least one glow plug was not in specified range. The technician will use that information, and use the scan tool to cycle the glow plugs on, then off. Reading circuit voltage for all of the glow plugs will show which one is faulty.

If the glow plug relay, injector pump timing, and engine compression are not properly checked, then replacing the glow plugs may not address the original problem.

Locations for glow plugs are mostly simple to access, and replacement requires that the battery is disconnected, the glow plug is disconnected from an electrical connection, and unscrewed like a spark plug. The threads in the cylinder head are inspected, cleaned, and, if specified, coated with an anti-seize compound. The old glow plug will be inspected for signs of the engine running poorly. The new glow plug is screwed in, then its connector is plugged in. After the battery is reconnected, the glow plugs should be tested on a cold start, preferably after several hours of sitting.

For best results and to avoid future problems, replace the glow plugs as a complete set. Be sure to verify that the glow plug relay is operating properly.