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Glow Plug Timer Relay Failure in Mercedes Vehicles

Mercedes Glow Plug

In most road-going vehicles, ignition and combustion processes are what give your car the power it needs in order to move. However, the different parts that aid these processes vary between vehicle designs. In a Mercedes-Benz diesel engine, the parts that help generate enough power differ from most vehicles; rather than utilizing spark plugs, they use something called a glow plug.

Glow plugs play a crucial role in your Mercedes performance, and therefore their wear and function must be monitored as time goes on. Unfortunately, certain models experience premature glow plug performance issues, specifically with the glow plug timer relay. If you’re unsure of what a glow plug timer relay is or what it does, don’t panic – in this blog, we’ll talk more about what a glow plug timer relay’s function is and what you can do to preserve the part.

Glow plug and timer relay functions

In your average car, spark plugs conduct high levels of heat that help to ignite or combust the fuel/oxygen mixture in your engine so that it can generate power to make the car move and gain momentum. However, as we mentioned before, Mercedes vehicles utilize a diesel engine model, which does not generally include spark plugs. Instead, glow plugs are the main source of heat for the engine cylinders, and when the glow plugs aren’t working properly the cylinders won’t fire.

Glow plugs use what is called a timer relay so that they know exactly what time frames and intervals to remain active for – this cuts down on unnecessarily wasted power, but it also makes sure that the glow plugs remain active for the appropriate amount of time, allowing them to generate enough heat for combustion. Without the timer relay, the glow plugs won’t function properly and you’ll likely run into some serious performance hiccups.

Warning signs of glow plug or related part failure

Just like spark plugs in an internal combustion engine, glow plugs themselves can wear out over time causing significant performance issues; however, other parts associated with the glow plugs, such as the timer relay, can also fail, which makes it difficult to determine whether the glow plugs themselves are the source of the problem or whether the symptoms are due to a timer relay issue. It is essential for you to be aware of the symptoms your Mercedes exhibits so that you can report them to your automotive specialist for accurate diagnosis. These are the typical signs of glow plug or related part failure:

Dashboard warning lights

Most vehicles today are essentially “smart” cars in that they have onboard computers to help detect when the car isn’t performing properly. In your Mercedes, the cars control unit detects when glow plugs or other related parts aren’t functioning optimally and relays that information to the driver via a warning light in the dashboard. Usually, if the problem is related to glow plugs or a timer relay, then one of two warning lights will appear: the check-engine light, or a specific glow plug service light. This is especially helpful for the diagnostic process.

Performance issues

As we’ve mentioned, when the glow plugs or timer relays aren’t functioning, there are a few performance-related issues you may run into, such as engine misfiring or a general decrease in power distribution. Usually, these problems don’t suddenly occur overnight with normal wear, so if you encounter these symptoms it’s critical to have the problem checked out by a Mercedes specialist right away.

Ignition issues

Along with general performance problems, you might also notice that your Mercedes is slow to start or has difficulty starting at all when the glow plug timer relay isn’t working. If the glow plug timer relay doesn’t communicate with the glow plugs to activate their power generation, then the engine likely won’t be able to start.

How to prevent glow plug related issues

Red Mercedes Sports CarThe Mercedes experts here at Pete’s, Inc. have been providing specialized German repair services to clients from all over the areas of Nob Hill, Pacific Heights, Russian Hill, and San Francisco, CA, for over 4 decades. If you’ve recently experienced any of the above-mentioned signs of glow plug timer relay issues or declining glow plugs themselves, please don’t hesitate to contact us for an inspection – we are confident that we can address the issue accurately, efficiently, and affordably.

*Red Mercedes Sports Car on Road image credit goes to: kurmyshov 



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