{"id":820,"date":"2026-03-15T14:24:55","date_gmt":"2026-03-15T18:24:55","guid":{"rendered":"https:\/\/www.4roadservice.com\/resources\/?page_id=820"},"modified":"2026-03-15T14:25:39","modified_gmt":"2026-03-15T18:25:39","slug":"detroit-diesel-spn-4375-fmi-18-def-doser-valve-response-fault","status":"publish","type":"page","link":"https:\/\/www.4roadservice.com\/resources\/detroit-diesel-spn-4375-fmi-18-def-doser-valve-response-fault\/","title":{"rendered":"Detroit Diesel SPN 4375 FMI 18 \u2013 DEF Doser Valve Response Fault (Meaning, Causes &amp; Fix)"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\"><a href=\"https:\/\/www.4roadservice.com\/resources\/detroit-diesel-fault-codes-dd13-dd15-dd16\/\">\u2190 Back to Detroit Diesel Fault Codes<\/a><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Detroit Diesel SPN 4375 FMI 18 indicates that the DEF doser valve is not responding as commanded by the ECM. This code appears on DD13, DD15, and DD16 engines and means the aftertreatment system cannot accurately control DEF delivery to the SCR catalyst, which will affect emissions performance and can lead to a derate condition if not resolved.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Symptoms<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Check engine light on <\/li>\n\n\n\n<li>DEF or SCR warning light illuminated <\/li>\n\n\n\n<li>Engine derate condition possible <\/li>\n\n\n\n<li>Reduced aftertreatment system performance <\/li>\n\n\n\n<li>May appear alongside other DEF dosing related codes<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">Cause<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">This code triggers when the ECM sends a command to the DEF doser valve and does not receive the expected response. Common causes include:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Stuck or seized doser valve due to DEF crystallization <\/li>\n\n\n\n<li>Electrical fault at the doser valve solenoid <\/li>\n\n\n\n<li>Damaged or corroded wiring harness to the valve <\/li>\n\n\n\n<li>Failed doser valve unable to open or close correctly <\/li>\n\n\n\n<li>DEF contamination causing valve to stick <\/li>\n\n\n\n<li>ECM communication fault with the doser valve circuit<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">Can You Keep Driving?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Limited driving may be possible but without proper doser valve response the SCR system cannot control DEF delivery accurately. The engine will likely enter a derate condition if the fault persists. Address this promptly to prevent further aftertreatment damage.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Recommended Action<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Inspect the DEF doser valve for signs of crystallization or physical damage. Check the valve wiring and connector for corrosion or damage. If the valve is crystallized it may be cleanable but replacement is often the more reliable fix. Have the valve solenoid tested for proper electrical response before condemning the part.<\/p>\n\n\n\n<div class=\"schema-faq wp-block-yoast-faq-block\"><div class=\"schema-faq-section\" id=\"faq-question-1773598831255\"><strong class=\"schema-faq-question\"><strong>What does Detroit Diesel SPN 4375 FMI 18 mean?<\/strong><\/strong> <p class=\"schema-faq-answer\">It means the DEF doser valve is not responding correctly to ECM commands, preventing accurate control of DEF delivery to the SCR catalyst.<\/p> <\/div> <div class=\"schema-faq-section\" id=\"faq-question-1773598833828\"><strong class=\"schema-faq-question\">What causes SPN 4375 FMI 18?<\/strong> <p class=\"schema-faq-answer\">The most common causes are a stuck or crystallized doser valve, an electrical fault at the valve solenoid, or damaged wiring in the doser valve circuit.<\/p> <\/div> <div class=\"schema-faq-section\" id=\"faq-question-1773598833420\"><strong class=\"schema-faq-question\"><strong>Can I keep driving with SPN 4375 FMI 18?<\/strong><\/strong> <p class=\"schema-faq-answer\">Short distances may be possible but without proper doser valve function the SCR system cannot operate correctly and a derate condition is likely to follow.<\/p> <\/div> <div class=\"schema-faq-section\" id=\"faq-question-1773598833044\"><strong class=\"schema-faq-question\">Will SPN 4375 FMI 18 cause a derate?<\/strong> <p class=\"schema-faq-answer\">Yes. If the ECM cannot control DEF dosing through the valve the SCR system will fail to meet emissions thresholds and a derate will be triggered.<\/p> <\/div> <div class=\"schema-faq-section\" id=\"faq-question-1773598832589\"><strong class=\"schema-faq-question\">How do I clear SPN 4375 FMI 18?<\/strong> <p class=\"schema-faq-answer\">Inspect, clean, or replace the DEF doser valve and verify wiring integrity. Once the valve responds correctly to ECM commands and the SCR system confirms proper DEF delivery the code should clear.<\/p> <\/div> <\/div>\n\n\n\n<h2 class=\"wp-block-heading\">Related codes<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li><a href=\"https:\/\/www.4roadservice.com\/resources\/detroit-diesel-spn-4076-fmi-18-def-dosing-injector-fault\/\" type=\"link\" id=\"https:\/\/www.4roadservice.com\/resources\/detroit-diesel-spn-4076-fmi-18-def-dosing-injector-fault\/\">SPN 4076 FMI 18 <\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/www.4roadservice.com\/resources\/detroit-diesel-spn-4094-fmi-18-def-dosing-low-flow\/\" type=\"link\" id=\"https:\/\/www.4roadservice.com\/resources\/detroit-diesel-spn-4094-fmi-18-def-dosing-low-flow\/\">SPN 4094 FMI 18 <\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/www.4roadservice.com\/resources\/detroit-diesel-spn-3362-fmi-1-def-pump-pressure-low\/\" type=\"link\" id=\"https:\/\/www.4roadservice.com\/resources\/detroit-diesel-spn-3362-fmi-1-def-pump-pressure-low\/\">SPN 3362 FMI 1 <\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/www.4roadservice.com\/resources\/detroit-diesel-spn-3363-fmi-16-def-pump-pressure-high\/\" type=\"link\" id=\"https:\/\/www.4roadservice.com\/resources\/detroit-diesel-spn-3363-fmi-16-def-pump-pressure-high\/\">SPN 3363 FMI 16<\/a><\/li>\n<\/ul>\n\n\n\n<div class=\"wp-block-group\"><div class=\"wp-block-group__inner-container is-layout-constrained wp-block-group-is-layout-constrained\">\n<h2 class=\"wp-block-heading\">Need Immediate Help With This Fault Code?<\/h2>\n<\/div><\/div>\n\n\n\n<p class=\"wp-block-paragraph\">If your engine is derating, losing power, or unable to complete regeneration, don\u2019t risk further damage or costly downtime.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Use 4RoadService to locate mobile truck repair, dealer diagnostics, or emergency roadside assistance near your location.<\/p>\n\n\n\n<div class=\"wp-block-buttons has-off-white-background-color has-background is-content-justification-center is-layout-flex wp-container-core-buttons-is-layout-fe48e5de wp-block-buttons-is-layout-flex\">\n<div class=\"wp-block-button\"><a class=\"wp-block-button__link wp-element-button\" href=\"https:\/\/www.4roadservice.com\/truck-dealers\">Find Truck Repair Near Me<\/a><\/div>\n\n\n\n<div class=\"wp-block-button\"><a class=\"wp-block-button__link has-text-align-center wp-element-button\" href=\"https:\/\/www.4roadservice.com\/truck-repair\">Find Mobile Road Service<\/a><\/div>\n<\/div>\n\n\n\n<h3 class=\"wp-block-heading\">Important Notice<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">The information provided above is for general informational purposes only and should not replace official OEM service procedures. Always consult the manufacturer\u2019s service manual or a qualified diesel technician before performing repairs. Operating a vehicle with active fault codes may result in further damage.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u2190 Back to Detroit Diesel Fault Codes Detroit Diesel SPN 4375 FMI 18 indicates that the DEF doser valve is not responding as commanded by the ECM. This code appears on DD13, DD15, and DD16 engines and means the aftertreatment system cannot accurately control DEF delivery to the SCR catalyst, which will affect emissions performance &hellip; <a href=\"https:\/\/www.4roadservice.com\/resources\/detroit-diesel-spn-4375-fmi-18-def-doser-valve-response-fault\/\" class=\"more-link\">Continue reading <span class=\"screen-reader-text\">Detroit Diesel SPN 4375 FMI 18 \u2013 DEF Doser Valve Response Fault (Meaning, Causes &amp; Fix)<\/span> <span class=\"meta-nav\">&rarr;<\/span><\/a><\/p>\n","protected":false},"author":4,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-820","page","type-page","status-publish","hentry"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v28.1 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>SPN 4375 FMI 18 \u2013 DEF Doser Valve Response Fault<\/title>\n<meta name=\"description\" content=\"Detroit Diesel SPN 4375 FMI 18 means the DEF doser valve is not responding correctly. 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Learn symptoms, causes, derate risk and how to fix it.\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.4roadservice.com\/resources\/detroit-diesel-spn-4375-fmi-18-def-doser-valve-response-fault\/\" \/>\n<meta property=\"og:site_name\" content=\"4RoadService Resources\" \/>\n<meta property=\"article:publisher\" content=\"https:\/\/www.facebook.com\/4roadservice\" \/>\n<meta property=\"article:modified_time\" content=\"2026-03-15T18:25:39+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/www.4roadservice.com\/resources\/wp-content\/uploads\/2015\/08\/logo-sidebar@2x.png\" \/>\n\t<meta property=\"og:image:width\" content=\"380\" \/>\n\t<meta property=\"og:image:height\" content=\"64\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/png\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:site\" content=\"@4RoadService\" \/>\n<meta name=\"twitter:label1\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data1\" content=\"3 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\\\/\\\/schema.org\",\"@graph\":[{\"@type\":[\"WebPage\",\"FAQPage\"],\"@id\":\"https:\\\/\\\/www.4roadservice.com\\\/resources\\\/detroit-diesel-spn-4375-fmi-18-def-doser-valve-response-fault\\\/\",\"url\":\"https:\\\/\\\/www.4roadservice.com\\\/resources\\\/detroit-diesel-spn-4375-fmi-18-def-doser-valve-response-fault\\\/\",\"name\":\"SPN 4375 FMI 18 \u2013 DEF Doser Valve Response Fault\",\"isPartOf\":{\"@id\":\"https:\\\/\\\/www.4roadservice.com\\\/resources\\\/#website\"},\"datePublished\":\"2026-03-15T18:24:55+00:00\",\"dateModified\":\"2026-03-15T18:25:39+00:00\",\"description\":\"Detroit Diesel SPN 4375 FMI 18 means the DEF doser valve is not responding correctly. 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Fix)"}]},{"@type":"WebSite","@id":"https:\/\/www.4roadservice.com\/resources\/#website","url":"https:\/\/www.4roadservice.com\/resources\/","name":"4RoadService Resources","description":"Tools, Repairs &amp; Resources for Truck Drivers","publisher":{"@id":"https:\/\/www.4roadservice.com\/resources\/#organization"},"potentialAction":[{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https:\/\/www.4roadservice.com\/resources\/?s={search_term_string}"},"query-input":{"@type":"PropertyValueSpecification","valueRequired":true,"valueName":"search_term_string"}}],"inLanguage":"en-US"},{"@type":"Organization","@id":"https:\/\/www.4roadservice.com\/resources\/#organization","name":"4RoadService.com","url":"https:\/\/www.4roadservice.com\/resources\/","logo":{"@type":"ImageObject","inLanguage":"en-US","@id":"https:\/\/www.4roadservice.com\/resources\/#\/schema\/logo\/image\/","url":"https:\/\/blog.4roadservice.com\/wp-content\/uploads\/2015\/08\/logo-sidebar@2x.png","contentUrl":"https:\/\/blog.4roadservice.com\/wp-content\/uploads\/2015\/08\/logo-sidebar@2x.png","width":380,"height":64,"caption":"4RoadService.com"},"image":{"@id":"https:\/\/www.4roadservice.com\/resources\/#\/schema\/logo\/image\/"},"sameAs":["https:\/\/www.facebook.com\/4roadservice","https:\/\/x.com\/4RoadService"]},{"@type":"Question","@id":"https:\/\/www.4roadservice.com\/resources\/detroit-diesel-spn-4375-fmi-18-def-doser-valve-response-fault\/#faq-question-1773598831255","position":1,"url":"https:\/\/www.4roadservice.com\/resources\/detroit-diesel-spn-4375-fmi-18-def-doser-valve-response-fault\/#faq-question-1773598831255","name":"What does Detroit Diesel SPN 4375 FMI 18 mean?","answerCount":1,"acceptedAnswer":{"@type":"Answer","text":"It means the DEF doser valve is not responding correctly to ECM commands, preventing accurate control of DEF delivery to the SCR catalyst.","inLanguage":"en-US"},"inLanguage":"en-US"},{"@type":"Question","@id":"https:\/\/www.4roadservice.com\/resources\/detroit-diesel-spn-4375-fmi-18-def-doser-valve-response-fault\/#faq-question-1773598833828","position":2,"url":"https:\/\/www.4roadservice.com\/resources\/detroit-diesel-spn-4375-fmi-18-def-doser-valve-response-fault\/#faq-question-1773598833828","name":"What causes SPN 4375 FMI 18?","answerCount":1,"acceptedAnswer":{"@type":"Answer","text":"The most common causes are a stuck or crystallized doser valve, an electrical fault at the valve solenoid, or damaged wiring in the doser valve circuit.","inLanguage":"en-US"},"inLanguage":"en-US"},{"@type":"Question","@id":"https:\/\/www.4roadservice.com\/resources\/detroit-diesel-spn-4375-fmi-18-def-doser-valve-response-fault\/#faq-question-1773598833420","position":3,"url":"https:\/\/www.4roadservice.com\/resources\/detroit-diesel-spn-4375-fmi-18-def-doser-valve-response-fault\/#faq-question-1773598833420","name":"Can I keep driving with SPN 4375 FMI 18?","answerCount":1,"acceptedAnswer":{"@type":"Answer","text":"Short distances may be possible but without proper doser valve function the SCR system cannot operate correctly and a derate condition is likely to follow.","inLanguage":"en-US"},"inLanguage":"en-US"},{"@type":"Question","@id":"https:\/\/www.4roadservice.com\/resources\/detroit-diesel-spn-4375-fmi-18-def-doser-valve-response-fault\/#faq-question-1773598833044","position":4,"url":"https:\/\/www.4roadservice.com\/resources\/detroit-diesel-spn-4375-fmi-18-def-doser-valve-response-fault\/#faq-question-1773598833044","name":"Will SPN 4375 FMI 18 cause a derate?","answerCount":1,"acceptedAnswer":{"@type":"Answer","text":"Yes. If the ECM cannot control DEF dosing through the valve the SCR system will fail to meet emissions thresholds and a derate will be triggered.","inLanguage":"en-US"},"inLanguage":"en-US"},{"@type":"Question","@id":"https:\/\/www.4roadservice.com\/resources\/detroit-diesel-spn-4375-fmi-18-def-doser-valve-response-fault\/#faq-question-1773598832589","position":5,"url":"https:\/\/www.4roadservice.com\/resources\/detroit-diesel-spn-4375-fmi-18-def-doser-valve-response-fault\/#faq-question-1773598832589","name":"How do I clear SPN 4375 FMI 18?","answerCount":1,"acceptedAnswer":{"@type":"Answer","text":"Inspect, clean, or replace the DEF doser valve and verify wiring integrity. Once the valve responds correctly to ECM commands and the SCR system confirms proper DEF delivery the code should clear.","inLanguage":"en-US"},"inLanguage":"en-US"}]}},"jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/P6wicq-de","_links":{"self":[{"href":"https:\/\/www.4roadservice.com\/resources\/wp-json\/wp\/v2\/pages\/820","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.4roadservice.com\/resources\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www.4roadservice.com\/resources\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www.4roadservice.com\/resources\/wp-json\/wp\/v2\/users\/4"}],"replies":[{"embeddable":true,"href":"https:\/\/www.4roadservice.com\/resources\/wp-json\/wp\/v2\/comments?post=820"}],"version-history":[{"count":5,"href":"https:\/\/www.4roadservice.com\/resources\/wp-json\/wp\/v2\/pages\/820\/revisions"}],"predecessor-version":[{"id":826,"href":"https:\/\/www.4roadservice.com\/resources\/wp-json\/wp\/v2\/pages\/820\/revisions\/826"}],"wp:attachment":[{"href":"https:\/\/www.4roadservice.com\/resources\/wp-json\/wp\/v2\/media?parent=820"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}