{"id":12656,"date":"2025-11-02T00:02:41","date_gmt":"2025-11-02T00:02:41","guid":{"rendered":"https:\/\/carexamer.com\/blog\/?p=12656"},"modified":"2026-02-17T22:20:55","modified_gmt":"2026-02-17T22:20:55","slug":"will-a-car-fail-mot-with-the-glow-plug-light-on","status":"publish","type":"post","link":"https:\/\/carexamer.com\/blog\/will-a-car-fail-mot-with-the-glow-plug-light-on\/","title":{"rendered":"Will a Car Fail MOT with the Glow Plug Light On?"},"content":{"rendered":"\n<p class=\"wp-block-yoast-seo-estimated-reading-time yoast-reading-time__wrapper\"><span class=\"yoast-reading-time__icon\"><svg aria-hidden=\"true\" focusable=\"false\" data-icon=\"clock\" width=\"20\" height=\"20\" fill=\"none\" stroke=\"currentColor\" style=\"display:inline-block;vertical-align:-0.1em\" role=\"img\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" viewBox=\"0 0 24 24\"><path stroke-linecap=\"round\" stroke-linejoin=\"round\" stroke-width=\"2\" d=\"M12 8v4l3 3m6-3a9 9 0 11-18 0 9 9 0 0118 0z\"><\/path><\/svg><\/span><span class=\"yoast-reading-time__spacer\" style=\"display:inline-block;width:1em\"><\/span><span class=\"yoast-reading-time__descriptive-text\">Estimated reading time: <\/span><span class=\"yoast-reading-time__reading-time\">5<\/span><span class=\"yoast-reading-time__time-unit\"> minutes<\/span><\/p>\n\n\n\n<p>If you drive a diesel car, you may have seen the <strong>glow plug warning light<\/strong> appear on your dashboard. This often raises an important question for drivers &#8211; will your car fail its <strong>MOT test<\/strong> if that light stays on? The glow plug system plays a crucial role in starting diesel engines, especially in cold conditions. However, when the light stays on or starts flashing, it can sometimes signal a deeper problem with the <strong>engine management system<\/strong>. In this guide, you will learn what the glow plug light means, how it affects the MOT test, and what typical repair costs look like in the UK.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"h-what-the-glow-plug-light-means\">What the Glow Plug Light Means<\/h2>\n\n\n\n<p>The glow plug light, shaped like a small coil or spring, appears on the dashboard when the ignition is turned on. It shows that the glow plugs are heating up the cylinders to help the engine start.<\/p>\n\n\n\n<p>Once the engine starts, the light should go off. If it stays on or flashes, it usually means there is a problem, such as:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>A <strong>faulty glow plug<\/strong> or relay<\/li>\n\n\n\n<li><strong>Wiring or sensor issues<\/strong><\/li>\n\n\n\n<li>A <strong>DPF (Diesel Particulate Filter) blockage<\/strong><\/li>\n\n\n\n<li>A <strong>faulty EGR valve<\/strong><\/li>\n\n\n\n<li><strong>Fuel injection or turbocharger problems<\/strong><\/li>\n<\/ul>\n\n\n\n<p>In many diesel cars, the glow plug light also works as an <strong>engine management warning<\/strong>, similar to the check engine light in petrol cars.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"h-will-a-car-fail-mot-with-the-glow-plug-light-on\">Will a Car Fail MOT with the Glow Plug Light On?<\/h2>\n\n\n\n<p>In most cases, <strong>yes<\/strong>, a car <strong>can fail its MOT<\/strong> if the glow plug light is flashing or stays on due to an engine fault.<\/p>\n\n\n\n<p>The <strong>DVSA (Driver and Vehicle Standards Agency)<\/strong> rules state that any illuminated <strong>engine management light (MIL)<\/strong> is a <strong>major defect<\/strong>, which means an automatic MOT failure.<\/p>\n\n\n\n<p>Because the glow plug light often acts as part of the diesel engine management system, a flashing or permanently lit light will usually be treated as an <strong>engine or emissions fault<\/strong> during the MOT.<\/p>\n\n\n\n<p>If the light comes on only before starting the engine and goes out once started, that is perfectly normal and will <strong>not cause a fail<\/strong>.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"h-common-causes-and-typical-uk-repair-costs\">Common Causes and Typical UK Repair Costs<\/h2>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>Cause<\/th><th>Description<\/th><th>Typical UK Repair Cost<\/th><\/tr><\/thead><tbody><tr><td>Faulty Glow Plug<\/td><td>Burnt or worn heating element<\/td><td>\u00a3100 \u2013 \u00a3200<\/td><\/tr><tr><td>Faulty Relay<\/td><td>Glow plug relay or fuse issue<\/td><td>\u00a380 \u2013 \u00a3150<\/td><\/tr><tr><td>EGR Valve Fault<\/td><td>Stuck or carbon build-up<\/td><td>\u00a3200 \u2013 \u00a3400<\/td><\/tr><tr><td>DPF Blockage<\/td><td>Exhaust filter full or clogged<\/td><td>\u00a3250 \u2013 \u00a3600<\/td><\/tr><tr><td>Sensor or Wiring Fault<\/td><td>ECU communication issue<\/td><td>\u00a3100 \u2013 \u00a3300<\/td><\/tr><tr><td>Turbocharger Fault<\/td><td>Boost control or pressure fault<\/td><td>\u00a3400 \u2013 \u00a3900<\/td><\/tr><\/tbody><\/table><figcaption class=\"wp-element-caption\">Repair costs<\/figcaption><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"h-what-happens-during-the-mot\">What Happens During the MOT<\/h2>\n\n\n\n<p>When carrying out the MOT, the tester will:<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li>Turn on the ignition to make sure dashboard warning lights come on.<\/li>\n\n\n\n<li>Start the engine to confirm the lights turn off correctly.<\/li>\n\n\n\n<li>Fail the car if the <strong>glow plug light<\/strong> or <strong>engine management light<\/strong> remains on or flashes.<\/li>\n<\/ol>\n\n\n\n<p>If the light indicates a <strong>DPF fault<\/strong> or other emissions issue, it will also cause an automatic failure under <strong>emissions defects<\/strong>.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"h-how-to-fix-the-glow-plug-light-before-mot\">How to Fix the Glow Plug Light Before MOT<\/h2>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Run a diagnostic scan<\/strong> to find out what is causing the warning.<\/li>\n\n\n\n<li><strong>Replace any faulty glow plugs or relay<\/strong>, which are common and inexpensive.<\/li>\n\n\n\n<li><strong>Clean or regenerate the DPF<\/strong> if the fault is emissions-related.<\/li>\n\n\n\n<li><strong>Repair or replace EGR valves or sensors<\/strong> if necessary.<\/li>\n\n\n\n<li><strong>Reset the system<\/strong> and drive the car to confirm the light stays off.<\/li>\n<\/ol>\n\n\n\n<p>A professional diagnostic scan usually costs between <strong>\u00a350 and \u00a380<\/strong> at most UK garages.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"h-is-it-safe-to-drive-with-the-glow-plug-light-on\">Is It Safe to Drive with the Glow Plug Light On?<\/h2>\n\n\n\n<p>If the light is <strong>steady<\/strong>, the car might still drive normally, although it may take longer to start.<\/p>\n\n\n\n<p>If the light is <strong>flashing<\/strong>, it could mean a more serious fault, such as a DPF or EGR issue. Continuing to drive could damage your engine or turbo, so you should get the fault checked immediately.<\/p>\n\n\n\n<p>Driving short distances to a garage is usually fine, but long journeys should be avoided until the problem is fixed.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"h-preventing-glow-plug-light-problems\">Preventing Glow Plug Light Problems<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Service your car regularly<\/strong> and keep to the manufacturer\u2019s schedule.<\/li>\n\n\n\n<li><strong>Replace glow plugs<\/strong> every 60,000 to 100,000 miles as preventative maintenance.<\/li>\n\n\n\n<li><strong>Use quality diesel fuel<\/strong> to prevent carbon build-up.<\/li>\n\n\n\n<li><strong>Drive longer journeys<\/strong> occasionally to allow the DPF to regenerate properly.<\/li>\n\n\n\n<li><strong>Check electrical connections<\/strong> for corrosion during servicing.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"h-mot-and-pre-purchase-inspection-advice\"><a href=\"https:\/\/carexamer.com\/free-mot-check\">MOT <\/a>and Pre-Purchase Inspection Advice<\/h2>\n\n\n\n<p>If you are <a href=\"https:\/\/carexamer.com\/blog\/category\/car-buying\/\">buying a used diesel <\/a>car and the <strong>glow plug light<\/strong> is flashing or staying on, it could mean there is an engine fault that will cause an MOT failure.<\/p>\n\n\n\n<p>A <strong>CAREXAMER pre-purchase inspection<\/strong> can identify whether the issue is a small sensor problem or a major engine or emissions fault before you buy the vehicle.<\/p>\n\n\n\n<p>For MOT testing, if the light is on or flashing when the engine is running, the car will <strong>fail<\/strong> and must be repaired before being retested.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"h-summary-of-glow-plug-light-causes\">Summary of Glow Plug Light Causes<\/h2>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>Problem<\/th><th>MOT Impact<\/th><th>Average UK Repair Cost<\/th><\/tr><\/thead><tbody><tr><td>Faulty Glow Plug<\/td><td>No MOT fail if minor<\/td><td>\u00a3100 \u2013 \u00a3200<\/td><\/tr><tr><td>Relay or Fuse Fault<\/td><td>Possible advisory<\/td><td>\u00a380 \u2013 \u00a3150<\/td><\/tr><tr><td>EGR or DPF Fault<\/td><td>MOT fail<\/td><td>\u00a3200 \u2013 \u00a3600<\/td><\/tr><tr><td>Sensor Fault<\/td><td>MOT fail if light on<\/td><td>\u00a3100 \u2013 \u00a3300<\/td><\/tr><tr><td>Turbo or Fuel Issue<\/td><td>MOT fail<\/td><td>\u00a3400 \u2013 \u00a3900<\/td><\/tr><\/tbody><\/table><figcaption class=\"wp-element-caption\">repair costs<\/figcaption><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"h-conclusion\">Conclusion<\/h2>\n\n\n\n<p>A <strong>car can fail its MOT if the glow plug light stays on or flashes<\/strong>, as this usually signals an engine management or emissions-related problem.<\/p>\n\n\n\n<p>Typical <strong>UK repair costs<\/strong> range from <strong>\u00a3100 for a simple glow plug replacement<\/strong> to <strong>\u00a3900 for major turbo or DPF faults<\/strong>.<\/p>\n\n\n\n<p>To avoid a MOT failure, identify and repair the cause early and make sure the warning light goes out before the test.<\/p>\n\n\n\n<p>If you are unsure, a <strong><a href=\"https:\/\/carexamer.com\/\">car inspection<\/a><\/strong> is an excellent way to find out whether the issue is minor or something more serious that could lead to an MOT fail.<\/p>\n\n\n\n<div class=\"wp-block-query is-layout-flow wp-block-query-is-layout-flow\"><ul class=\"wp-block-post-template is-layout-flow wp-block-post-template-is-layout-flow\"><li class=\"wp-block-post post-10266 post type-post status-publish format-standard has-post-thumbnail hentry category-car-buying category-driving-articles\">\n\n<div class=\"wp-block-columns are-vertically-aligned-center is-layout-flex wp-container-core-columns-is-layout-9d6595d7 wp-block-columns-is-layout-flex\">\n<div class=\"wp-block-column is-vertically-aligned-center is-layout-flow wp-block-column-is-layout-flow\" style=\"flex-basis:25%\"><figure class=\"wp-block-post-featured-image\"><a href=\"https:\/\/carexamer.com\/blog\/this-car-has-no-faults-phrase-used-car-sellers-always-use\/\" target=\"_self\"  ><img decoding=\"async\" width=\"1512\" height=\"868\" src=\"https:\/\/carexamer.com\/blog\/wp-content\/uploads\/2025\/01\/This-Car-Has-No-Faults-What-Used-Car-Sellers-Dont-Want-You-to-Know.jpg\" class=\"attachment-post-thumbnail size-post-thumbnail wp-post-image\" alt=\"\u201cThis Car Has No Faults!\u201d Phrase Used Car Sellers Always Use\" style=\"object-fit:cover;\" srcset=\"https:\/\/carexamer.com\/blog\/wp-content\/uploads\/2025\/01\/This-Car-Has-No-Faults-What-Used-Car-Sellers-Dont-Want-You-to-Know.jpg 1512w, https:\/\/carexamer.com\/blog\/wp-content\/uploads\/2025\/01\/This-Car-Has-No-Faults-What-Used-Car-Sellers-Dont-Want-You-to-Know-300x172.jpg 300w, https:\/\/carexamer.com\/blog\/wp-content\/uploads\/2025\/01\/This-Car-Has-No-Faults-What-Used-Car-Sellers-Dont-Want-You-to-Know-1024x588.jpg 1024w, https:\/\/carexamer.com\/blog\/wp-content\/uploads\/2025\/01\/This-Car-Has-No-Faults-What-Used-Car-Sellers-Dont-Want-You-to-Know-768x441.jpg 768w\" sizes=\"(max-width: 1512px) 100vw, 1512px\" \/><\/a><\/figure><\/div>\n\n\n\n<div class=\"wp-block-column is-vertically-aligned-center is-layout-flow wp-block-column-is-layout-flow\" style=\"flex-basis:75%\"><h2 class=\"wp-block-post-title\"><a href=\"https:\/\/carexamer.com\/blog\/this-car-has-no-faults-phrase-used-car-sellers-always-use\/\" target=\"_self\" >\u201cThis Car Has No Faults!\u201d Phrase Used Car Sellers Always Use<\/a><\/h2><\/div>\n<\/div>\n\n<\/li><li class=\"wp-block-post post-5009 post type-post status-publish format-standard has-post-thumbnail hentry category-car-buying\">\n\n<div class=\"wp-block-columns are-vertically-aligned-center is-layout-flex wp-container-core-columns-is-layout-9d6595d7 wp-block-columns-is-layout-flex\">\n<div class=\"wp-block-column is-vertically-aligned-center is-layout-flow wp-block-column-is-layout-flow\" style=\"flex-basis:25%\"><figure class=\"wp-block-post-featured-image\"><a href=\"https:\/\/carexamer.com\/blog\/10-best-cars-for-first-time-drivers\/\" target=\"_self\"  ><img decoding=\"async\" width=\"2560\" height=\"1704\" src=\"https:\/\/carexamer.com\/blog\/wp-content\/uploads\/2021\/10\/pexels-pixabay-38637-scaled.jpg\" class=\"attachment-post-thumbnail size-post-thumbnail wp-post-image\" alt=\"10 Best Cars for First Time Drivers\" style=\"object-fit:cover;\" srcset=\"https:\/\/carexamer.com\/blog\/wp-content\/uploads\/2021\/10\/pexels-pixabay-38637-scaled.jpg 2560w, https:\/\/carexamer.com\/blog\/wp-content\/uploads\/2021\/10\/pexels-pixabay-38637-300x200.jpg 300w, https:\/\/carexamer.com\/blog\/wp-content\/uploads\/2021\/10\/pexels-pixabay-38637-1024x681.jpg 1024w, https:\/\/carexamer.com\/blog\/wp-content\/uploads\/2021\/10\/pexels-pixabay-38637-768x511.jpg 768w, https:\/\/carexamer.com\/blog\/wp-content\/uploads\/2021\/10\/pexels-pixabay-38637-1536x1022.jpg 1536w, https:\/\/carexamer.com\/blog\/wp-content\/uploads\/2021\/10\/pexels-pixabay-38637-2048x1363.jpg 2048w\" sizes=\"(max-width: 2560px) 100vw, 2560px\" \/><\/a><\/figure><\/div>\n\n\n\n<div class=\"wp-block-column is-vertically-aligned-center is-layout-flow wp-block-column-is-layout-flow\" style=\"flex-basis:75%\"><h2 class=\"wp-block-post-title\"><a href=\"https:\/\/carexamer.com\/blog\/10-best-cars-for-first-time-drivers\/\" target=\"_self\" >10 Best Cars for First Time Drivers<\/a><\/h2><\/div>\n<\/div>\n\n<\/li><li class=\"wp-block-post post-5719 post type-post status-publish format-standard has-post-thumbnail hentry category-driving-articles\">\n\n<div class=\"wp-block-columns are-vertically-aligned-center is-layout-flex wp-container-core-columns-is-layout-9d6595d7 wp-block-columns-is-layout-flex\">\n<div class=\"wp-block-column is-vertically-aligned-center is-layout-flow wp-block-column-is-layout-flow\" style=\"flex-basis:25%\"><figure class=\"wp-block-post-featured-image\"><a href=\"https:\/\/carexamer.com\/blog\/10-best-small-european-used-cars\/\" target=\"_self\"  ><img decoding=\"async\" width=\"1920\" height=\"1440\" src=\"https:\/\/carexamer.com\/blog\/wp-content\/uploads\/2023\/06\/10-Best-Small-European-Used-Cars.jpg\" class=\"attachment-post-thumbnail size-post-thumbnail wp-post-image\" alt=\"10 Best Small European Used Cars: Combining Style and Performance on a Budget\" style=\"object-fit:cover;\" srcset=\"https:\/\/carexamer.com\/blog\/wp-content\/uploads\/2023\/06\/10-Best-Small-European-Used-Cars.jpg 1920w, https:\/\/carexamer.com\/blog\/wp-content\/uploads\/2023\/06\/10-Best-Small-European-Used-Cars-300x225.jpg 300w, https:\/\/carexamer.com\/blog\/wp-content\/uploads\/2023\/06\/10-Best-Small-European-Used-Cars-1024x768.jpg 1024w, https:\/\/carexamer.com\/blog\/wp-content\/uploads\/2023\/06\/10-Best-Small-European-Used-Cars-768x576.jpg 768w, https:\/\/carexamer.com\/blog\/wp-content\/uploads\/2023\/06\/10-Best-Small-European-Used-Cars-1536x1152.jpg 1536w\" sizes=\"(max-width: 1920px) 100vw, 1920px\" \/><\/a><\/figure><\/div>\n\n\n\n<div class=\"wp-block-column is-vertically-aligned-center is-layout-flow wp-block-column-is-layout-flow\" style=\"flex-basis:75%\"><h2 class=\"wp-block-post-title\"><a href=\"https:\/\/carexamer.com\/blog\/10-best-small-european-used-cars\/\" target=\"_self\" >10 Best Small European Used Cars: Combining Style and Performance on a Budget<\/a><\/h2><\/div>\n<\/div>\n\n<\/li><\/ul><\/div>\n","protected":false},"excerpt":{"rendered":"<p>If you drive a diesel car, you may have seen the glow plug warning light appear on your dashboard. This<\/p>\n","protected":false},"author":2,"featured_media":12657,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[28],"tags":[],"class_list":["post-12656","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-car-problems-and-repair-costs"],"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v23.0 (Yoast SEO v23.1) - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>Will a Car Fail MOT with the Glow Plug Light On?<\/title>\n<meta name=\"description\" content=\"Find out if your car will fail its MOT with the glow plug light on. 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