{"id":66467,"date":"2022-02-03T23:26:06","date_gmt":"2022-02-04T07:26:06","guid":{"rendered":"https:\/\/blogv2prod.wpenginepowered.com\/blog\/?p=66467"},"modified":"2024-12-17T18:03:06","modified_gmt":"2024-12-18T02:03:06","slug":"p0178-code-fuel-composition-sensor-circuit-low","status":"publish","type":"post","link":"https:\/\/www.carparts.com\/blog\/p0178-code-fuel-composition-sensor-circuit-low\/","title":{"rendered":"P0178 Code: Fuel Composition Sensor Circuit Low"},"content":{"rendered":"<!DOCTYPE html PUBLIC \"-\/\/W3C\/\/DTD HTML 4.0 Transitional\/\/EN\" \"http:\/\/www.w3.org\/TR\/REC-html40\/loose.dtd\">\n<html><body><span class=\"span-reading-time rt-reading-time\" style=\"display: block;\"><span class=\"rt-label rt-prefix\">Reading Time: <\/span> <span class=\"rt-time\"> 5<\/span> <span class=\"rt-label rt-postfix\">minutes<\/span><\/span><style>.kadence-column66467_1f1070-18 > .kt-inside-inner-col,.kadence-column66467_1f1070-18 > .kt-inside-inner-col:before{border-top-left-radius:0px;border-top-right-radius:0px;border-bottom-right-radius:0px;border-bottom-left-radius:0px;}.kadence-column66467_1f1070-18 > .kt-inside-inner-col{column-gap:var(--global-kb-gap-sm, 1rem);}.kadence-column66467_1f1070-18 > .kt-inside-inner-col{flex-direction:column;}.kadence-column66467_1f1070-18 > .kt-inside-inner-col > .aligncenter{width:100%;}.kadence-column66467_1f1070-18 > .kt-inside-inner-col:before{opacity:0.3;}.kadence-column66467_1f1070-18{position:relative;}@media all and (max-width: 1024px){.kadence-column66467_1f1070-18 > .kt-inside-inner-col{flex-direction:column;justify-content:center;}}@media all and (max-width: 767px){.kadence-column66467_1f1070-18 > .kt-inside-inner-col{flex-direction:column;justify-content:center;}}<\/style>\n<div class=\"wp-block-kadence-column kadence-column66467_1f1070-18 inner-column-1 qk-look-widget\"><div class=\"kt-inside-inner-col\">\n<div class=\"wp-block-ultimate-post-row ultp-block-a2783a  qk-main-wrap\"><div class=\"ultp-row-wrapper\"><div class=\"ultp-row-content\">\n<div class=\"wp-block-ultimate-post-column ultp-block-e4d890\"><div class=\"ultp-column-wrapper\"><style>.wp-block-kadence-advancedheading.kt-adv-heading66467_be3543-a8, .wp-block-kadence-advancedheading.kt-adv-heading66467_be3543-a8[data-kb-block=\"kb-adv-heading66467_be3543-a8\"]{text-align:center;font-size:20px;font-style:normal;}.wp-block-kadence-advancedheading.kt-adv-heading66467_be3543-a8 mark.kt-highlight, .wp-block-kadence-advancedheading.kt-adv-heading66467_be3543-a8[data-kb-block=\"kb-adv-heading66467_be3543-a8\"] mark.kt-highlight{font-family:Inter;font-weight:500;font-style:normal;color:#f76a0c;-webkit-box-decoration-break:clone;box-decoration-break:clone;padding-top:0px;padding-right:0px;padding-bottom:0px;padding-left:0px;}.wp-block-kadence-advancedheading.kt-adv-heading66467_be3543-a8 img.kb-inline-image, .wp-block-kadence-advancedheading.kt-adv-heading66467_be3543-a8[data-kb-block=\"kb-adv-heading66467_be3543-a8\"] img.kb-inline-image{width:150px;vertical-align:baseline;}<\/style>\n<div class=\"kt-adv-heading66467_be3543-a8 summary-title wp-block-kadence-advancedheading\" data-kb-block=\"kb-adv-heading66467_be3543-a8\"><span>Summary<\/span><\/div>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The diagnostic trouble code (DTC) P0178 stands for &ldquo;Fuel Composition Sensor Circuit Low.&rdquo;&nbsp;<\/li>\n\n\n\n<li>Your vehicle&rsquo;s powertrain control module (PCM) will log code P0178 when the fuel composition sensor sends a signal voltage that is lower than it should be.<\/li>\n\n\n\n<li>Common causes of the P0178 code are a bad fuel composition sensor, a faulty PCM, and outdated PCM software.<\/li>\n\n\n\n<li>The symptoms of the P0178 code include an illuminated check engine light, engine performance problems, and the engine failing to start.<\/li>\n<\/ul>\n<\/div><\/div>\n<\/div><\/div><\/div>\n<\/div><\/div>\n\n\n\n\n\n<p>The fuel composition sensor measures the ratio of ethanol to gasoline in vehicles equipped with flexible fuel systems. It sends its readings to the powertrain control module (PCM), which tweaks parameters, such as fuel delivery and ignition timing, in response.<\/p>\n\n\n\n<p>If the <a href=\"https:\/\/www.carparts.com\/engine-control-module\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"PCM\">PCM<\/a> detects the wrong electrical signal from the fuel composition sensor, it will set the engine code P0178.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">What Does the P0178 Code Mean?<\/h2>\n\n\n\n<p>The <a href=\"https:\/\/www.carparts.com\/blog\/search-obd2-codes-list\/\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"Diagnostic Trouble Code\">Diagnostic Trouble Code<\/a> (DTC) P0178 indicates &ldquo;Fuel Composition Sensor Circuit Low.&rdquo;<\/p>\n\n\n\n<figure class=\"wp-block-image size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"602\" src=\"https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2022\/02\/flex-fuel-sensor-isolated-1024x602.jpg\" alt=\"flex fuel sensor isolated\" class=\"wp-image-66475\" srcset=\"https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2022\/02\/flex-fuel-sensor-isolated-1024x602.jpg 1024w, https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2022\/02\/flex-fuel-sensor-isolated-300x176.jpg 300w, https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2022\/02\/flex-fuel-sensor-isolated-768x452.jpg 768w, https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2022\/02\/flex-fuel-sensor-isolated-1536x904.jpg 1536w, https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2022\/02\/flex-fuel-sensor-isolated-150x88.jpg 150w, https:\/\/www.carparts.com\/blog\/wp-content\/uploads\/2022\/02\/flex-fuel-sensor-isolated.jpg 1700w\" sizes=\"(max-width: 1024px) 100vw, 1024px\"><figcaption class=\"wp-element-caption\"> Also called a &ldquo;flex fuel sensor,&rdquo; the fuel composition sensor measures the percentage of ethanol in the fuel.<\/figcaption><\/figure>\n\n\n\n<p>Most vehicles can only burn fuels with a maximum of 10-15 percent ethanol alcohol before their engine starts developing issues. That&rsquo;s because <a href=\"https:\/\/www.carparts.com\/blog\/can-you-mix-ethanol-and-non-ethanol-gas-in-your-car\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"ethanol fuel\">ethanol fuel<\/a> has a higher octane rating and burns leaner than gasoline. A flexible fuel system lets the vehicle burn fuel with as much as 85 percent ethanol (E85).<\/p>\n\n\n\n<p>Also called the &ldquo;flex fuel sensor,&rdquo; the fuel composition sensor measures the percentage of ethanol in the fuel. It sends the appropriate frequency modulated signal to the PCM. Lower voltages indicate low ethanol levels while higher voltages show that the ratio is skewed toward ethanol.<\/p>\n\n\n\n<p>The readings from the fuel composition sensor tell the PCM how to adjust parameters like the amount of fuel sprayed into the engine&rsquo;s cylinders and the timing of the spark plugs&rsquo; ignition. This makes the sensor and its electrical circuit invaluable to making sure the engine gets the right amount of ethanol fuel.<\/p>\n\n\n\n<p>The PCM regularly checks the signals from the fuel composition sensor. If the signal voltage is lower than what it should be, the computer will set the P0178 code &ldquo;Fuel Composition Sensor Circuit Low.&rdquo; This typically means the frequency of the sensor is below a certain range.<\/p>\n\n\n\n<p>GM describes the operation of the fuel composition sensor this way:<\/p>\n\n\n\n<p><em>The PCM provides an internal pull up to 5&thinsp;volts on the signal circuit, and the FCS pulls the 5&thinsp;volts to ground in pulses. The normal range of operating frequency is between 50&ndash;150&thinsp;Hz. The normal pulse width ranges between 1&ndash;5&thinsp;milliseconds. If the PCM detects a signal less than 45&thinsp;Hz DTC&thinsp;P0178 will set.<\/em><\/p>\n\n\n\n<p>You can find more information that can help you better understand codes like P0178 in our technical discussion about the <a href=\"#Note_About_the_Fuel_Composition_Sensor\" target=\"_blank\" rel=\"noreferrer noopener nofollow\" aria-label=\"fuel composition sensor\">fuel composition sensor<\/a>.<\/p>\n\n\n\n<p><em><strong>Note:<\/strong> The definition of code P0178 may differ according to the vehicle manufacturer. Check the appropriate repair manual or repair database for the exact code definition.<\/em><\/p>\n\n\n\n<div id=\"article-search-widget\">\n<div class=\"cp-search\">\n<div align=\"center\">\n<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cld.partsimg.com\/image\/upload\/w_auto,dpr_auto\/carparts\/logos\/badge_wordmark\/full_color\/CP_LOGO_COLOUR_RGB\" alt=\"CarParts.com\" width=\"300\" height=\"56\">\n<\/div>\n<form id=\"cpsearchform\" name=\"cpsearchform\" action=\"https:\/\/www.carparts.com\/search\" method=\"get\" target=\"_blank\" accept-charset=\"character_set\" aria-label=\"search CarParts.com\">\n    <input type=\"text\" class=\"keyword\" name=\"q\" placeholder=\"Search for parts on CarParts.com\" value=\"\" aria-label=\"Search CarParts.com\"><input type=\"submit\" class=\"btn-search\" value=\"Search\" aria-label=\"Search\">\n<\/form>\n<\/div>\n<\/div>\n\n\n\n<h2 class=\"wp-block-heading\">What are the Common Causes of the P0178 Code?<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Faulty <a href=\"https:\/\/www.carparts.com\/flex-fuel-sensor\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"fuel composition sensor\">fuel composition sensor<\/a><\/li>\n\n\n\n<li>Faulty PCM<\/li>\n\n\n\n<li>Outdated PCM software that needs updating<\/li>\n\n\n\n<li>Problems with the fuel composition sensor <a href=\"https:\/\/www.carparts.com\/blog\/car-wiring\/\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"wiring\">wiring<\/a> or <a href=\"https:\/\/www.carparts.com\/flex-fuel-sensor-connector\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"connectors\">connectors<\/a><\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">What are the Common Symptoms of the P0178 Code?<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li><a href=\"https:\/\/www.carparts.com\/blog\/check-engine-light-flashing\/\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"Illuminated check engine light\">Illuminated check engine light<\/a><\/li>\n\n\n\n<li>Engine engine performance problems, such as stalling and poor performance<\/li>\n\n\n\n<li><a href=\"https:\/\/www.carparts.com\/blog\/my-car-wont-start-what-should-i-do\/\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"Engine fails to start\">Engine fails to start<\/a><\/li>\n\n\n\n<li>More fuel consumed and wasted<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">How to Diagnose the P0178 Code<\/h2>\n\n\n\n<p>The DTC P0178 is a generic engine code. It applies to many OBD-compatible vehicles that can burn flex fuel.<\/p>\n\n\n\n<p>If you&rsquo;re not confident about conducting diagnostic tests on your vehicle&rsquo;s fuel position sensor circuit, it&rsquo;s a good idea to bring it to a professional mechanic. Otherwise, you may go ahead and diagnose the issue yourself.<\/p>\n\n\n\n<p>Check out this video to learn more about what the diagnostic procedure might entail:<\/p>\n\n\n\n<figure class=\"wp-block-embed is-type-video is-provider-youtube wp-block-embed-youtube wp-embed-aspect-16-9 wp-has-aspect-ratio\"><div class=\"wp-block-embed__wrapper\">\n<iframe loading=\"lazy\" title=\"Chevrolet Suburban - GMC Yukon Code P0178\" width=\"500\" height=\"281\" src=\"https:\/\/www.youtube.com\/embed\/1X7Ynl1L2oc?feature=oembed\" frameborder=\"0\" allow=\"accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share\" referrerpolicy=\"strict-origin-when-cross-origin\" allowfullscreen><\/iframe>\n<\/div><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\">How to Fix the P0178 Code<\/h2>\n\n\n\n<p>Trying to repair a P0178 code may become a frustrating task if you lack the right tools and knowledge to test the faulty fuel composition sensor, PCM, and wiring. In most cases, it&rsquo;s best to leave the job to professionals.<\/p>\n\n\n\n<p>For DIYers with advanced technical knowledge and hands-on experience who prefer to test and replace their vehicle&rsquo;s fuel composition sensor on their own, it will be helpful to rely on the appropriate <a href=\"https:\/\/www.carparts.com\/blog\/why-you-should-always-consult-a-repair-manual\/\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"repair manual or refer to an online repair database\">repair manual or refer to an online repair database<\/a>.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Note About the Fuel Composition Sensor<\/h2>\n\n\n\n<p>Not all flex fuel vehicles use a fuel composition sensor. Some use algorithms in the engine controller and O2 sensor input to determine fueling strategy.<\/p>\n\n\n\n<p>But for just one example, on GM vehicles equipped with fuel composition sensors (FCS), the fuel flows through the sensor, which produces a Hertz (cycles per second) signal the ECM\/PCM uses to determine alcohol content. The FCS is a three-wire sensor with an internal microprocessor.<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p>Not all flex fuel vehicles use a fuel composition sensor. Some use algorithms in the engine controller and O2 sensor input to determine fueling strategy.<\/p>\n<cite><em>&ndash;&nbsp;<\/em><a href=\"https:\/\/www.carparts.com\/blog\/author\/richardmccuistian\/\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"Richard McCuistian, ASE Certified Master Automobile Technician\">Richard McCuistian, ASE Certified Master Automobile Technician<\/a><\/cite><\/blockquote>\n\n\n\n<p>The FCS uses a microprocessor inside the sensor to measure the ethanol percentage and fuel temperature, and changes output signals accordingly. The signal circuit carries both the ethanol percentage, and the fuel temperature within the same signal. The signal is both variable frequency and variable pulse width. The frequency signal indicates the ethanol percentage and the pulse width indicates fuel temperature.<\/p>\n\n\n\n<p>If the FCS over-reports the alcohol content, it can cause hard starting concerns even if no diagnostic trouble code is stored, because the ECM\/PCM has no way of knowing whether the FCS is telling the truth or not if the failure is what is known as an &ldquo;in range&rdquo; failure.&rdquo; And there are no rationality checks to verify alcohol content.<\/p>\n\n\n\n<p>Where an in-range failure is concerned, if the ECM\/PCM believes the alcohol content of the fuel is, let&rsquo;s say, 50% when the fuel is actually only 10% alcohol, the ECM&rsquo;s algorithms will over-fuel the engine during cold starting and foul the spark plugs. This hard start\/no-start concern may be intermittent. It may start sometimes and not other times. If the scan tool is reporting fuel alcohol levels that are known to be much higher than the known alcohol content of fuel, this may be the case.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Where to Get a New Fuel Sensor Connectors for Your Car<\/h2>\n\n\n\n<p>Eager to drive your vehicle, but the P0178 won&rsquo;t let you? If the fix requires you to replace the <a href=\"https:\/\/www.carparts.com\/flex-fuel-sensor-connector\" target=\"_blank\" rel=\"noreferrer noopener\" aria-label=\"fuel sensor connectors\">fuel sensor connectors<\/a>, then don&rsquo;t put it off. Order high-quality connectors today at <a href=\"http:\/\/carparts.com\" target=\"_blank\" rel=\"noreferrer noopener nofollow\" aria-label=\"CarParts.com\">CarParts.com<\/a>.<\/p>\n\n\n\n<p>Our fuel sensors are handpicked by a team of industry professionals to ensure they pass the highest quality control standards.<\/p>\n\n\n\n<p>Shopping with us is easy. You can start by entering your vehicle&rsquo;s year, make, and model into our vehicle selector to narrow the catalog to compatible connectors for your car. You can also use our search filters to match the results according to your preferred brand or price.<\/p>\n\n\n\n<p>We also have warehouses strategically located across the US to ensure you get your order on time. You can expect your new connectors to arrive in as fast as two business days.<\/p>\n\n\n\n<p>Our products also come with a low-price and lifetime replacement guarantee. So check out our catalog today, and get the best deals on CarParts.com!<\/p>\n<\/body><\/html>\n","protected":false},"excerpt":{"rendered":"<p><span class=\"span-reading-time rt-reading-time\" style=\"display: block;\"><span class=\"rt-label rt-prefix\">Reading Time: <\/span> <span class=\"rt-time\"> 5<\/span> <span class=\"rt-label rt-postfix\">minutes<\/span><\/span>The fuel composition sensor measures the ratio of ethanol to gasoline in vehicles equipped with flexible fuel systems. It sends&#8230; <a href=\"https:\/\/www.carparts.com\/blog\/p0178-code-fuel-composition-sensor-circuit-low\/\" rel=\"nofollow\">Read More<\/a><\/p>\n","protected":false},"author":4,"featured_media":66476,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":true,"_genesis_hide_title":false,"_genesis_hide_breadcrumbs":false,"_genesis_hide_singular_image":false,"_genesis_hide_footer_widgets":false,"_genesis_custom_body_class":"","_genesis_custom_post_class":"","_genesis_layout":"","footnotes":""},"categories":[1314],"tags":[3185],"ppma_author":[2607,2985],"class_list":{"0":"post-66467","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-obd-ii-trouble-codes","8":"tag-flex-fuel-sensor","9":"entry"},"acf":{"adrotate_specific_mobile_ad":"","adrotate_specific_desktop_ad":""},"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.4 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>P0178 Code: Fuel Composition Sensor Circuit Low - In The Garage with CarParts.com<\/title>\n<meta name=\"description\" content=\"Learn what the P0178 code means, its possible causes, common symptoms, and the right way to solve the issue. Read on.\" \/>\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.carparts.com\/blog\/p0178-code-fuel-composition-sensor-circuit-low\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"P0178 Code: Fuel Composition Sensor Circuit Low - In The Garage with CarParts.com\" \/>\n<meta property=\"og:description\" content=\"Learn what the P0178 code means, its possible causes, common symptoms, and the right way to solve the issue. 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