{"id":667,"date":"2026-02-22T13:58:19","date_gmt":"2026-02-22T18:58:19","guid":{"rendered":"https:\/\/www.4roadservice.com\/resources\/?page_id=667"},"modified":"2026-02-22T21:28:12","modified_gmt":"2026-02-23T02:28:12","slug":"detroit-diesel-spn-171-fmi-3","status":"publish","type":"page","link":"https:\/\/www.4roadservice.com\/resources\/detroit-diesel-spn-171-fmi-3\/","title":{"rendered":"Detroit Diesel SPN 171 FMI 3 \u2013 Ambient Air Temperature Sensor Voltage High (Meaning &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 171 FMI 3 indicates that the ambient air temperature sensor is reporting a voltage signal above the expected range. This can affect fuel management and emissions performance.<\/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 illuminated<\/li>\n\n\n\n<li>Incorrect temperature readings<\/li>\n\n\n\n<li>Reduced fuel efficiency<\/li>\n\n\n\n<li>Possible aftertreatment warnings<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">Cause<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">This fault is commonly caused by wiring issues, short circuits, damaged connectors, or a failed ambient temperature sensor.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Can You Keep Driving?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Driving may be possible temporarily, but continued operation with low fuel pressure may cause engine stalling or additional damage.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Recommended Action<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Inspect wiring and connectors for damage. Test the ambient air temperature sensor and replace if necessary.<\/p>\n\n\n\n<div class=\"schema-faq wp-block-yoast-faq-block\"><div class=\"schema-faq-section\" id=\"faq-question-1771790529711\"><strong class=\"schema-faq-question\">What does Detroit Diesel SPN 171 FMI 3 mean?<\/strong> <p class=\"schema-faq-answer\">SPN 171 FMI 3 indicates that the ambient air temperature sensor is reporting a voltage higher than the expected range.<\/p> <\/div> <div class=\"schema-faq-section\" id=\"faq-question-1771790530818\"><strong class=\"schema-faq-question\">What causes SPN 171 FMI 3?<\/strong> <p class=\"schema-faq-answer\">Common causes include a faulty ambient temperature sensor, shorted wiring, damaged connectors, or electrical issues in the sensor circuit.<\/p> <\/div> <div class=\"schema-faq-section\" id=\"faq-question-1771790531594\"><strong class=\"schema-faq-question\">Can I keep driving with SPN 171 FMI 3?<\/strong> <p class=\"schema-faq-answer\">Driving is typically possible, but inaccurate temperature readings can affect fuel management and emissions performance.<\/p> <\/div> <div class=\"schema-faq-section\" id=\"faq-question-1771790532186\"><strong class=\"schema-faq-question\">Will SPN 171 FMI 3 cause a derate?<\/strong> <p class=\"schema-faq-answer\">In most cases it does not immediately cause a derate, but unresolved sensor faults can contribute to performance or emissions-related issues.<\/p> <\/div> <div class=\"schema-faq-section\" id=\"faq-question-1771790532858\"><strong class=\"schema-faq-question\">How do I fix SPN 171 FMI 3?<\/strong> <p class=\"schema-faq-answer\">Inspect wiring and connectors for damage, test the ambient air temperature sensor, and replace it if voltage readings remain outside specification.<\/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-102-fmi-18\/\">SPN 102 (Boost)<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/www.4roadservice.com\/resources\/detroit-diesel-spn-94-fmi-1\/\">SPN 94 (Fuel Pressure)<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/www.4roadservice.com\/resources\/detroit-diesel-spn-1569-fmi-31\/\">SPN 1569 (Derate)<\/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 171 FMI 3 indicates that the ambient air temperature sensor is reporting a voltage signal above the expected range. This can affect fuel management and emissions performance. Symptoms Cause This fault is commonly caused by wiring issues, short circuits, damaged connectors, or a failed ambient &hellip; <a href=\"https:\/\/www.4roadservice.com\/resources\/detroit-diesel-spn-171-fmi-3\/\" class=\"more-link\">Continue reading <span class=\"screen-reader-text\">Detroit Diesel SPN 171 FMI 3 \u2013 Ambient Air Temperature Sensor Voltage High (Meaning &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-667","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>Detroit Diesel SPN 171 FMI 3 \u2013 Ambient Temp Sensor Fix<\/title>\n<meta name=\"description\" content=\"Detroit Diesel SPN 171 FMI 3 indicates high voltage from the ambient air temperature sensor. 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