--- title: "Glow Plug Warning Light MOT Advisory: Diesel Starting Issues" canonical: https://www.carbuyeriq.com/guides/mot-advisories-explained/glow-plug-warning-light-mot-advisory-diesel-starting-issues last_updated: 6 November 2026 category: MOT Advisories Explained source: CarBuyerIQ --- # Glow Plug Warning Light MOT Advisory: Diesel Starting Issues ## Understanding the Glow Plug Warning Light Advisory When you receive your MOT results and see a glow plug warning light advisory, it can be a cause for concern, especially if you drive a diesel vehicle. In plain English, this advisory indicates that there may be an issue with the glow plugs in your engine. Glow plugs are essential components in diesel engines, designed to heat the combustion chamber for easier starting, particularly in colder weather. If they are not functioning correctly, you may experience starting difficulties, rough idling, or increased emissions. The glow plug system operates by pre-heating the air in the combustion chamber before the engine starts. This is particularly important for diesel engines, which rely on compression ignition rather than spark plugs. If the glow plugs are faulty, the engine may struggle to start, leading to potential long-term damage if not addressed. Understanding what this advisory means is crucial for any diesel vehicle owner, as it can affect both performance and safety. ## How Serious Is a Glow Plug Advisory? The seriousness of a glow plug advisory can vary significantly depending on the specific symptoms your vehicle exhibits. At one end of the spectrum, it might be a minor annoyance, especially if the vehicle starts without much trouble. However, if the glow plugs are severely degraded, you could face significant starting issues, particularly in colder temperatures. This could leave you stranded or lead to further complications, such as increased wear on the starter motor and battery. If you are weighing up alternatives, our guide to [Tyre Pressure Monitoring System Faulty MOT Advisory](https://www.carbuyeriq.com/guides/mot-advisories-explained/tyre-pressure-monitoring-system-faulty-mot-advisory-is-it-serious) covers similar ground from a different angle. In some cases, a malfunctioning glow plug can cause the engine to misfire, leading to rough idling and increased emissions. This not only affects the vehicle's performance but could also result in failing future MOT tests due to emissions standards. Therefore, while it may not seem critical at first glance, ignoring a glow plug advisory can lead to a cascade of issues that could compromise your vehicle's reliability and safety. ## Typical Repair Costs for Glow Plug Issues The cost of repairing glow plug issues can vary widely based on the make and model of your vehicle, as well as the extent of the problem. Generally, you can expect to pay between £100 and £300 for glow plug replacement. This price typically includes the cost of parts and labour, but it can increase if additional issues are discovered during the repair process. For more on this topic, take a look at our [EGR Valve Faulty MOT Advisory](https://www.carbuyeriq.com/guides/mot-advisories-explained/egr-valve-faulty-mot-advisory-common-on-diesels) guide. For example, if the glow plugs are found to be faulty due to a more significant electrical issue, such as a failing relay or wiring problems, the repair costs could rise significantly. It's also worth noting that some vehicles require more labour-intensive procedures to access the glow plugs, which can further increase the overall cost. As a rule of thumb, it's advisable to get a few quotes from different garages to ensure you're getting a fair price. ## How Urgent Is the Repair? Determining the urgency of addressing a glow plug advisory depends on how your vehicle is performing. If your diesel engine starts reliably and runs smoothly, you might be able to postpone repairs for a short period. However, if you notice that the engine struggles to start, particularly in colder weather, it’s wise to address the issue sooner rather than later. You might also find our [Exhaust Has Minor Leak MOT Advisory](https://www.carbuyeriq.com/guides/mot-advisories-explained/exhaust-has-minor-leak-mot-advisory-how-much-to-fix) guide useful alongside this one. Delaying repairs can lead to more severe problems, including damage to the starter motor or battery, which can be significantly more expensive to fix. If you find yourself frequently needing to jump-start your vehicle or if the glow plug warning light remains illuminated, it’s a clear sign that you should seek professional assistance as soon as possible. Ignoring the advisory could lead to a situation where your vehicle becomes undriveable, leaving you with no choice but to pay for more extensive repairs. ## What to Watch For If the Advisory Appears Repeatedly If you receive a glow plug advisory multiple times during your MOT tests, it’s essential to take it seriously. Repeated advisories can indicate a persistent underlying issue that needs addressing. For instance, it could suggest that the glow plugs are not just worn out but that there may be a more significant electrical problem affecting the entire glow plug system. We have covered related ground in our [Steering Rack Worn](https://www.carbuyeriq.com/guides/mot-advisories-explained/mot-steering-rack-worn-repair-cost) guide, which is worth reading if this subject interests you. You should also be vigilant for any accompanying symptoms. If the glow plug warning light keeps coming on, pay attention to how the vehicle starts and runs. Are you experiencing rough idling, excessive smoke from the exhaust, or a noticeable drop in fuel efficiency? These could all be signs of a deeper issue that requires immediate attention. In such cases, it’s advisable to consult a qualified mechanic who can perform a thorough diagnostic check to identify the root cause of the problem. ## Impact on Vehicle Value and Negotiation Position A glow plug advisory can have a significant impact on your vehicle's value, especially if you are considering selling or trading it in. Potential buyers may view the advisory as a red flag, leading them to question the overall reliability of the vehicle. This could result in a lower offer than you might expect, as buyers often factor in the cost of necessary repairs when negotiating. You can check the exact safety score for any model on the [Euro NCAP website](https://www.euroncap.com/en). If you find yourself in a position where you need to negotiate the sale of your vehicle, it’s crucial to be transparent about the advisory. Providing potential buyers with the full MOT history can help build trust and demonstrate that you are not trying to hide any issues. You can check your vehicle's MOT history for free on the [GOV.UK website](https://www.gov.uk/check-mot-history), which can provide valuable insights into past advisories and repairs. Additionally, if you have already addressed the glow plug issue and can provide receipts for the repairs, this can strengthen your negotiating position. Buyers are often willing to pay a premium for a vehicle that has been well-maintained and has no outstanding issues. ## Conclusion Receiving a glow plug warning light advisory during your MOT can be concerning, but understanding what it means and how to address it can help you make informed decisions about your vehicle. While it may initially seem like a minor issue, the potential for starting problems and increased emissions should not be underestimated. If you notice any symptoms associated with faulty glow plugs, it’s advisable to seek repairs promptly to avoid further complications. Additionally, keep an eye on any repeated advisories, as these could indicate a more significant issue that needs addressing. When it comes time to sell or trade your vehicle, being transparent about any advisories and repairs can help you maintain its value and negotiate effectively. For peace of mind, always check your vehicle's full MOT history, which can provide crucial information about its past performance and any recurring issues. You can do this easily through the [GOV.UK MOT history checker](https://www.gov.uk/check-mot-history). By staying informed and proactive, you can ensure that your diesel vehicle remains reliable and safe on the road. --- Source: CarBuyerIQ, "Glow Plug Warning Light MOT Advisory: Diesel Starting Issues", https://www.carbuyeriq.com/guides/mot-advisories-explained/glow-plug-warning-light-mot-advisory-diesel-starting-issues (last updated 6 November 2026).