{"id":79065,"date":"2025-07-16T19:37:23","date_gmt":"2025-07-17T00:37:23","guid":{"rendered":"https:\/\/www.emanualonline.com\/blog\/?p=79065"},"modified":"2025-07-16T19:37:23","modified_gmt":"2025-07-17T00:37:23","slug":"p0c21-obd2-auxiliary-transmission-fluid-pump-phase-u-v-w-circuit-low","status":"publish","type":"post","link":"https:\/\/www.emanualonline.com\/blog\/p0c21-obd2-auxiliary-transmission-fluid-pump-phase-u-v-w-circuit-low","title":{"rendered":"P0C21 OBD2: AUXILIARY Transmission Fluid Pump Phase U-V-W Circuit Low"},"content":{"rendered":"<p>The P0C21 OBD-II code indicates a malfunction related to the auxiliary transmission fluid pump. This code is categorized as urgent, meaning immediate action is necessary to prevent severe damage to the vehicle.<\/p>\n<h2>What Does the P0C21 Code Mean?<\/h2>\n<p>The P0C21 code is defined as an AUXILIARY Transmission Fluid Pump Phase U-V-W Circuit Low error. This code signals that the electric motor responsible for the auxiliary transmission fluid pump is not functioning correctly, specifically in its phase U-V-W circuit.<\/p>\n<h2>What Causes the P0C21 Code?<\/h2>\n<p>The primary cause of the P0C21 code is related to the Motor Control Module (MCM), which is part of the Drive Motor Generator Power Inverter Control Module. The MCM monitors the high voltage system that drives the transmission. If the voltage is outside the acceptable range, the transmission may fail to move the vehicle, triggering the P0C21 code.<\/p>\n<h2>What Are the Symptoms of the P0C21 Code?<\/h2>\n<ul>\n<li>Vehicle may be immovable<\/li>\n<li>Warning lights on the dashboard<\/li>\n<\/ul>\n<h2>How Serious Is the P0C21 Code?<\/h2>\n<p>This code is considered urgent. If it is not addressed promptly, it can lead to severe damage to the transmission system or pose safety risks to the driver and passengers.<\/p>\n<h2>How to Diagnose the P0C21 Code<\/h2>\n<p>Diagnosing the P0C21 code involves using an OBD-II scanner to confirm the presence of the code. Technicians will also check the high voltage circuits, inspect the auxiliary transmission pump, and test the Motor Control Module for faults.<\/p>\n<h2>Common Repairs for the P0C21 Code<\/h2>\n<ul>\n<li>Replacing the auxiliary transmission pump<\/li>\n<li>Repairing or replacing the Drive Motor Generator Power Inverter Control Module<\/li>\n<li>Fixing wiring issues or shorts in the high voltage circuit<\/li>\n<\/ul>\n<h2>How Much Does It Cost to Fix the P0C21 Code?<\/h2>\n<p>The repair costs for the P0C21 code can vary widely depending on the specific issue. Typical costs can range from $200 to $1,500, depending on whether you need to replace the auxiliary pump or the control module.<\/p>\n<h2>Can I Fix the P0C21 Code Myself?<\/h2>\n<p>While some experienced mechanics may attempt to diagnose and repair the P0C21 code themselves, it is crucial to have a proper understanding of the vehicle&#8217;s electrical systems and the potential risks involved. If you&#8217;re not confident in your skills, it&#8217;s best to seek professional assistance.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>The P0C21 OBD-II code indicates a malfunction related to the auxiliary transmission fluid pump. This code is categorized as urgent, meaning immediate action is necessary to prevent severe damage to the vehicle. What Does the P0C21 Code Mean? The P0C21 code is defined as an AUXILIARY Transmission Fluid Pump Phase U-V-W Circuit Low error. This &hellip;<\/p>\n","protected":false},"author":26,"featured_media":90487,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"om_disable_all_campaigns":false,"_uag_custom_page_level_css":"","footnotes":""},"categories":[11987],"tags":[],"class_list":["post-79065","post","type-post","status-publish","format-standard","has-post-thumbnail","","category-p-obd2-codes-powertrain"],"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v28.3 (Yoast SEO v28.3) - https:\/\/yoast.com\/product\/yoast-seo-premium-wordpress\/ -->\n<title>OBD2 Code P0C21 \u2013 Causes, Symptoms, and Repairs<\/title>\n<meta name=\"description\" content=\"Learn all about the P0C21 code, what causes AUXILIARY Transmission Fluid Pump Phase U-V-W Circuit Low, and how to diagnose and fix common issues to maintain optimal vehicle performance.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.emanualonline.com\/blog\/p0c21-obd2-auxiliary-transmission-fluid-pump-phase-u-v-w-circuit-low\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"P0C21 OBD2: AUXILIARY Transmission Fluid Pump Phase U-V-W Circuit Low\" \/>\n<meta property=\"og:description\" content=\"The P0C21 OBD-II code indicates a malfunction related to the auxiliary transmission fluid pump. This code is categorized as urgent, meaning immediate\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.emanualonline.com\/blog\/p0c21-obd2-auxiliary-transmission-fluid-pump-phase-u-v-w-circuit-low\" \/>\n<meta property=\"og:site_name\" content=\"eManualOnline Blog\" \/>\n<meta property=\"article:publisher\" content=\"https:\/\/www.facebook.com\/EmanualOnline\/\" \/>\n<meta property=\"article:published_time\" content=\"2025-07-17T00:37:23+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/www.emanualonline.com\/blog\/wp-content\/uploads\/2025\/07\/p0c21-obd2-auxiliary-transmission-fluid-pump-phase-u-v-w-circuit-low.png\" \/>\n\t<meta property=\"og:image:width\" content=\"1200\" \/>\n\t<meta property=\"og:image:height\" content=\"675\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/png\" \/>\n<meta name=\"author\" content=\"JC Landry\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:creator\" 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He's worked across dealerships, owned and operated his own independent garage, and consulted on automotive trade school curricula, reviewing technical textbooks used in vocational programs. He now serves as Editor-in-Chief at eManualOnline.com, where he oversees the platform's technical content. He's one of the few voices in automotive publishing who has actually turned wrenches professionally on the vehicles he covers. He didn't learn automotive repair to write about it. He learned to write after spending over a decade doing it.","sameAs":["https:\/\/www.linkedin.com\/in\/jean-claude-landry-857781186\/"],"url":"https:\/\/www.emanualonline.com\/blog\/author\/jclandry"}]}},"uagb_featured_image_src":{"full":["https:\/\/www.emanualonline.com\/blog\/wp-content\/uploads\/2025\/07\/p0c21-obd2-auxiliary-transmission-fluid-pump-phase-u-v-w-circuit-low.png",1200,675,false],"thumbnail":["https:\/\/www.emanualonline.com\/blog\/wp-content\/uploads\/2025\/07\/p0c21-obd2-auxiliary-transmission-fluid-pump-phase-u-v-w-circuit-low-150x150.png",150,150,true],"medium":["https:\/\/www.emanualonline.com\/blog\/wp-content\/uploads\/2025\/07\/p0c21-obd2-auxiliary-transmission-fluid-pump-phase-u-v-w-circuit-low-300x169.png",300,169,true],"medium_large":["https:\/\/www.emanualonline.com\/blog\/wp-content\/uploads\/2025\/07\/p0c21-obd2-auxiliary-transmission-fluid-pump-phase-u-v-w-circuit-low-768x432.png",618,348,true],"large":["https:\/\/www.emanualonline.com\/blog\/wp-content\/uploads\/2025\/07\/p0c21-obd2-auxiliary-transmission-fluid-pump-phase-u-v-w-circuit-low-1024x576.png",618,348,true],"1536x1536":["https:\/\/www.emanualonline.com\/blog\/wp-content\/uploads\/2025\/07\/p0c21-obd2-auxiliary-transmission-fluid-pump-phase-u-v-w-circuit-low.png",1200,675,false],"2048x2048":["https:\/\/www.emanualonline.com\/blog\/wp-content\/uploads\/2025\/07\/p0c21-obd2-auxiliary-transmission-fluid-pump-phase-u-v-w-circuit-low.png",1200,675,false],"tie-small":["https:\/\/www.emanualonline.com\/blog\/wp-content\/uploads\/2025\/07\/p0c21-obd2-auxiliary-transmission-fluid-pump-phase-u-v-w-circuit-low-110x75.png",110,75,true],"tie-medium":["https:\/\/www.emanualonline.com\/blog\/wp-content\/uploads\/2025\/07\/p0c21-obd2-auxiliary-transmission-fluid-pump-phase-u-v-w-circuit-low-403x215.png",403,215,true],"tie-large":["https:\/\/www.emanualonline.com\/blog\/wp-content\/uploads\/2025\/07\/p0c21-obd2-auxiliary-transmission-fluid-pump-phase-u-v-w-circuit-low-310x205.png",310,205,true],"slider":["https:\/\/www.emanualonline.com\/blog\/wp-content\/uploads\/2025\/07\/p0c21-obd2-auxiliary-transmission-fluid-pump-phase-u-v-w-circuit-low-660x330.png",660,330,true],"big-slider":["https:\/\/www.emanualonline.com\/blog\/wp-content\/uploads\/2025\/07\/p0c21-obd2-auxiliary-transmission-fluid-pump-phase-u-v-w-circuit-low-1050x525.png",1050,525,true]},"uagb_author_info":{"display_name":"JC Landry","author_link":"https:\/\/www.emanualonline.com\/blog\/author\/jclandry"},"uagb_comment_info":0,"uagb_excerpt":"The P0C21 OBD-II code indicates a malfunction related to the auxiliary transmission fluid pump. This code is categorized as urgent, meaning immediate action is necessary to prevent severe damage to the vehicle. What Does the P0C21 Code Mean? The P0C21 code is defined as an AUXILIARY Transmission Fluid Pump Phase U-V-W Circuit Low error. 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