{"id":4099,"date":"2024-11-08T07:37:25","date_gmt":"2024-11-08T15:37:25","guid":{"rendered":"\/wp-site\/?p=4099"},"modified":"2025-07-14T18:37:44","modified_gmt":"2025-07-15T01:37:44","slug":"how-to-test-alternator-by-disconnecting-battery","status":"publish","type":"car-repair","link":"https:\/\/jerry.ai\/car-repair\/how-to-test-alternator-by-disconnecting-battery\/","title":{"rendered":"How to Test Your Alternator by Disconnecting Battery: A Step-By-Step Guide"},"content":{"rendered":"\n<p><strong>You can test alternators by disconnecting negative battery cables and using a voltage meter.<\/strong><\/p>\n\n\n\n<blockquote class=\"wp-block-jerry-key-takeaway border-primary flex flex-col rounded bg-gray-50 p-6 border-l-0\"><div class=\"flex flex-col md:block md:space-x-1\"><span class=\"has-primary-color text-lg font-semibold\">QUICK LOOK<\/span><span class=\"text-gray-900 text-base\"><\/span><\/div><div class=\"jerry-block-content\" contentclassname=\"text-gray-900 text-base\">\n<ul class=\"wp-block-list\">\n<li>The alternator is one of the most important electrical components of your car<\/li>\n\n\n\n<li>Without a functioning alternator, your car can\u2019t start<\/li>\n\n\n\n<li>Disconnecting the car battery is one of the most popular DIY alternator tests, but it\u2019s not always a good idea because it can kill your voltage regulator and\/or cause a massive voltage spike that damages your car\u2019s electrical system<\/li>\n<\/ul>\n<\/div><\/blockquote>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity is-style-separator-jerry-default\"\/>\n\n\n\n<p><strong>LEARN MORE<\/strong>: <a href=\"\/car-insurance\/\" data-type=\"car-insurance\" data-id=\"29872\">How to save on car insurance<\/a><\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity is-style-separator-jerry-default\"\/>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"how-do-you-know-your-car-alternator-is-bad\">How do you know your car alternator is bad?<\/h2>\n\n\n\n<p>The alternator provides your car with electricity and recharges the vehicle\u2019s battery by turning mechanical energy into electrical energy. Think of it as your car\u2019s personal charging system.<\/p>\n\n\n\n<p>A failing alternator won\u2019t have enough power to properly charge the battery while the car engine is running, which could eventually leave you unable to start your vehicle after your battery dies.<\/p>\n\n\n\n<p>Here are some common symptoms of a faulty alternator you should look out for:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Dim lights<\/li>\n\n\n\n<li>Dead battery<\/li>\n\n\n\n<li>Illuminated dashboard lights (such as a battery warning light)<\/li>\n\n\n\n<li>Electrical problems<\/li>\n\n\n\n<li>Burning rubber or wire smell<\/li>\n\n\n\n<li>Trouble starting or frequent stalling<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"how-to-test-alternators-by-disconnecting-the-battery\">How to test alternators by disconnecting the battery<\/h2>\n\n\n\n<p>If your car is having trouble starting or the battery won&#8217;t hold a charge, you may be dealing with a bad alternator\u2014but it could also be a bad battery.<\/p>\n\n\n\n<p>You can confirm that your alternator is failing by disconnecting the battery and performing a simple test.<\/p>\n\n\n\n<p>However, just because it\u2019s a simple test doesn\u2019t mean it is a safe test for you or your vehicle. That\u2019s why it\u2019s important to pay attention to the steps below\u2014or leave the test to a mechanic if you don\u2019t have the technical know-how.<\/p>\n\n\n\n<h3 class=\"wp-block-heading has-medium-font-size\">1. Park in a safe place<\/h3>\n\n\n\n<p>This alternator test should always be performed in an open space away from structures, trees, or any other flammable materials. Your driveway or an empty parking lot can both be good places to conduct this test if they are open!<\/p>\n\n\n\n<h3 class=\"wp-block-heading has-medium-font-size\">2. Get the engine running<\/h3>\n\n\n\n<p>Place your car in park before you start your engine. Keep your car running in the parked position while performing the alternator test.<\/p>\n\n\n\n<p>Before moving on to the next step you may want to put on a pair of heat-resistant rubber gloves to avoid burning yourself on the hot engine.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">3. Find the positive and negative battery terminals<\/h3>\n\n\n\n<p>Pop open the hood of your car and hook it into place so you can identify the positive and negative battery terminals. Car battery terminals are color-coded and marked so they can be easily identified. The positive battery terminal is red with a plus (+) sign and the negative battery terminal will be black and have a minus (\u2013) sign.<\/p>\n\n\n\n<p>If your battery recently died, the negative and positive battery terminals are where you connect the jumper cables when you jump-start your car!<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">4. Disconnect the negative battery terminal<\/h3>\n\n\n\n<p>Once you\u2019ve correctly identified the negative and positive terminals, you can disconnect your car battery to test your alternator.<\/p>\n\n\n\n<p>While the engine is running, remove the cable to disconnect the negative battery terminal.<\/p>\n\n\n\n<p><strong>Make sure you do not disconnect the positive battery terminal:<\/strong> This could cause a spark and irreparable damage to your computer system.<\/p>\n\n\n\n<p>A good alternator will keep the engine running after you\u2019ve disconnected the negative battery terminal, but if the engine performance decreases, stalls, or dies out your alternator may be faulty. However, a failing alternator could still produce just enough energy to keep your engine running, so you\u2019ll need to run further diagnostics to be certain.<\/p>\n\n\n\n<blockquote class=\"wp-block-jerry-key-takeaway border-primary flex flex-col rounded bg-gray-50 p-6 border-l-4\"><div class=\"flex flex-col md:block md:space-x-1\"><span class=\"has-primary-color text-lg font-semibold\">Key Takeaway<\/span><span class=\"text-gray-900 text-base\">Make sure you disconnect the negative battery terminal when conducting the alternator test as disconnecting the positive terminal will damage your car&#8217;s electrical computer system.<\/span><\/div><div class=\"jerry-block-content\" contentclassname=\"text-gray-900 text-base\"><\/div><\/blockquote>\n\n\n\n<h3 class=\"wp-block-heading has-medium-font-size\">5. Run a voltage test using a voltmeter<\/h3>\n\n\n\n<p>While the negative terminal is disconnected, use a voltmeter to measure the battery voltage and check if there is a voltage between car battery terminals. You\u2019ll take two voltage readings: one with all the car accessories turned off and the other with them all turned on.<\/p>\n\n\n\n<p>The first voltage reading should give a score of 14 volts and the second should be at least 13 volts. If your voltage tests are reading scores of less than those numbers, that\u2019s a good indicator you have a bad alternator.<\/p>\n\n\n\n<p>Don\u2019t have a voltmeter? They\u2019re pretty easy to find on Amazon for $30 or less.<\/p>\n\n\n\n<h3 class=\"wp-block-heading has-medium-font-size\">6. Test the alternator using a multimeter<\/h3>\n\n\n\n<p>A multimeter measures voltage, electric current, and resistance whereas a voltmeter only measures voltage. Using a multimeter is a good test because it will deliver the most comprehensive readings.<\/p>\n\n\n\n<p><strong>Here\u2019s how you test the alternator using a multimeter:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Turn off your vehicle:<\/strong> If your vehicle isn\u2019t off already, turn it off<\/li>\n\n\n\n<li><strong>Prepare your multimeter:<\/strong> Adjust your multimeter voltage to 20 DC volts or if it doesn\u2019t have an incremental setting simply set it to DC volts<\/li>\n\n\n\n<li><strong>Press the probes to your battery terminals:<\/strong> Touch each multimeter probe to the correct terminals, connecting positive to positive and negative to negative<\/li>\n\n\n\n<li><strong>Take the battery reading:<\/strong> The voltage reading should read between 12.4 and 12.6 volts. If it\u2019s below this, you could have a bad battery<\/li>\n\n\n\n<li><strong>Start your vehicle and check the reading:<\/strong> Press the probes to the battery terminals and the multimeter should read 14 to 14.5 volts. If the voltage is lower than your initial reading, then the charger is not working<\/li>\n<\/ul>\n\n\n\n<p><strong>If the engine performance decreased when you disconnected the car battery and both voltmeter and multimeter voltage readings were below 14 volts:<\/strong> You\u2019ll need to head to an automotive repair shop to get a new alternator.<\/p>\n\n\n\n<div class=\"wp-block-jerry-cta\"><div class=\"flex flex-col items-start gap-4 rounded-xl border border-zinc-200 px-12 py-8 md:flex-row md:items-center md:gap-14\"><div class=\"flex-1\"><span class=\"text-xl font-black text-gray-900\">YOU\u2019RE MINUTES AWAY FROM SIMPLIFIED CAR MAINTENANCE<\/span><\/div><div class=\"flex-1\"><a href=\"\/signup\/addcaryear?service=garage\" class=\"bg-primary block w-full rounded-full px-14 py-2 text-center font-black text-white hover:no-underline\">Get Started for Free<\/a><\/div><\/div><\/div>\n\n\n\n<div class=\"!mbs-12 !mbe-12 wp-block-jerry-faqs wp-block-jerry-faqs\">\n  <!-- Title -->\n    <h2 class=\"medium-title text-black mb-1.5 pt-12 uppercase\">\n    FAQ  <\/h2>\n  \n  <!-- Accordion -->\n  \n<div class=\"max-w-screen-lg my-6 [&amp;_li:last-child]:border-b-0\">\n<ul class=\"wp-block-jerry-accordion\">\n<li class=\"font-circular flex cursor-pointer list-none flex-col items-start gap-1 border-b border-zinc-200 py-6 text-lg text-slate-500 md:flex-row md:gap-5 wp-block-jerry-accordion-item font-circular flex cursor-pointer flex-row items-start border-b border-zinc-200 py-6 text-lg text-slate-500 is-style-accordion-item-box wp-block-jerry-accordion-item\" data-wp-interactive=\"accordion-item\" data-wp-init=\"callbacks.onInit\">\n  <!-- Accessory -->\n  \n  <div class=\"flex flex-1 flex-col text-gray-600\">\n    <div class=\"flex flex-row items-start justify-between gap-4\">\n      <!-- Title -->\n      <span class=\"accordion-q align-middle text-black font-medium\">\n        Which battery terminal do you disconnect to test the alternator?      <\/span>\n\n      <!-- Icon -->\n      <span class=\"accordion-i text-black font-medium mr-4 mt-1 shrink-0 align-middle transition iconify i--chevron-down\"><\/span>\n    <\/div>\n\n    <!-- Content -->\n    \n<div class=\"jerry-block-content accordion-a mt-5 hidden\">\n<p>You\u2019ll disconnect the negative battery terminal to test the alternator. If you disconnect the positive battery terminal it could cause serious damage to your car&#8217;s computer system.<\/p>\n<\/div>\n  <\/div>\n<\/li>\n\n\n\n<li class=\"font-circular flex cursor-pointer list-none flex-col items-start gap-1 border-b border-zinc-200 py-6 text-lg text-slate-500 md:flex-row md:gap-5 wp-block-jerry-accordion-item font-circular flex cursor-pointer flex-row items-start border-b border-zinc-200 py-6 text-lg text-slate-500 is-style-accordion-item-box wp-block-jerry-accordion-item\" data-wp-interactive=\"accordion-item\" data-wp-init=\"callbacks.onInit\">\n  <!-- Accessory -->\n  \n  <div class=\"flex flex-1 flex-col text-gray-600\">\n    <div class=\"flex flex-row items-start justify-between gap-4\">\n      <!-- Title -->\n      <span class=\"accordion-q align-middle text-black font-medium\">\n        What happens if your alternator goes out while driving?      <\/span>\n\n      <!-- Icon -->\n      <span class=\"accordion-i text-black font-medium mr-4 mt-1 shrink-0 align-middle transition iconify i--chevron-down\"><\/span>\n    <\/div>\n\n    <!-- Content -->\n    \n<div class=\"jerry-block-content accordion-a mt-5 hidden\">\n<p>If your alternator fails while driving, your battery should still have enough power for your car. However, you should pull over and call a tow truck if you notice your lights flickering, the radio turning off, or other power issues.<\/p>\n<\/div>\n  <\/div>\n<\/li>\n<\/ul>\n<\/div>\n\n  <!-- Contact link -->\n  <\/div>\n\n\n\n<div class=\"wp-block-jerry-meet-experts\" data-wp-interactive=\"jerry\/meet-experts\" data-wp-context=\"{&quot;modalVisible&quot;:false}\">\n  <div class=\"font-circular text-2xl font-extrabold text-slate-900\">Expert-driven. Built for you.<\/div>\n\n  <div class=\"my-3\">\n    <div class=\"flex justify-between items-center py-3 border-b border-neutral-200 cursor-pointer font-semibold text-gray-900\" data-wp-on-async--click=\"actions.toggleModal\">\n  <button class=\"text-left text-base\" type=\"button\">\n    Why you can count on Jerry&#8217;s articles  <\/button>\n\n  <div class=\"transition data-[visible=true]:md:rotate-180 text-xs iconify i--chevron-down text-gray-500\" data-wp-bind--data-visible=\"context.modalVisible\"><\/div>\n<\/div>\n<div class=\"modal-backdrop fixed bottom-0 left-0 right-0 top-0 z-50 overflow-hidden overscroll-contain bg-black\/70 font-body transition-transform delay-100 duration-0 md:relative md:z-auto [&amp;:not([data-visible=true])]:translate-y-full [&amp;:not([data-visible=true])]:bg-black\/0 [&amp;:not([data-visible=true])]:md:hidden\" data-wp-init=\"callbacks.onModalInit\" data-wp-on-async--click=\"actions.hideModal\" data-wp-bind--data-visible=\"context.modalVisible\">\n  <div class=\"modal-view fixed bottom-0 left-0 right-0 flex max-h-[75%] w-full flex-col rounded-t-3xl bg-white pb-7 pl-7 pt-3.5 transition md:relative md:rounded-none md:pl-0 md:transition-none [&amp;:not([data-visible=true])]:translate-y-full [&amp;:not([data-visible=true])]:md:hidden\" data-wp-bind--data-visible=\"context.modalVisible\">\n    <div class=\"modal-header md:hidden flex justify-between items-center pb-1 mb-1 border-b border-zinc-200\">\n      <div class=\"modal-title text-base font-semibold\">Summary<\/div>\n\n      <div\n        class=\"modal-close-btn wp-block-group w-11 h-11 mr-2.5 content-center text-center\"\n        data-wp-on-async--click=\"actions.hideModal\"\n      >\n        <div class=\"iconify i--close text-gray-500 cursor-pointer\"><\/div>\n      <\/div>\n    <\/div>\n\n    <div class=\"modal-body pr-7 overflow-y-auto\"><div class=\"wp-block-template-part\"><div class=\"flex flex-row items-center gap-2.5 rounded-lg bg-gray-pink px-4 py-5\">\n  <span class=\"iconify mt-0.5 shrink-0 self-start text-xs text-primary i--shield-check\"><\/span>\n\n  <div>\n    <div class=\"font-body text-xs font-bold text-primary\">Our goal is clear, trustworthy information.<\/div>\n    <div class=\"mt-1 font-body text-xs text-gray-600\">\n      Our content is created, edited and fact checked by a team of licensed insurance agents, automotive pros and\n      experienced journalists who know the industry inside and out. Facts are thoroughly researched, verified and kept\n      current, and our editorial team is separate from our business partners, so our opinions &#038; tips are unbiased. All\n      insights drawn from Jerry\u2019s proprietary, aggregated customer auto insurance quotes data provide unique, real-world\n      guidance.\n    <\/div>\n  <\/div>\n<\/div>\n<\/div><\/div>\n  <\/div>\n<\/div>\n  <\/div>\n\n  <div class=\"text-base font-semibold text-gray-900\">Our experts<\/div>\n\n  <div class=\"my-8 flex flex-col gap-8 items-center justify-center\">\n          <div\n        class=\"meet-experts-item group relative flex h-auto w-full flex-none flex-col justify-between overflow-hidden rounded-3xl py-9 text-sm shadow-variant-card\"\n        data-expand=\"false\"\n        data-wp-init=\"callbacks.onItemInit\"\n      >\n        <div class=\"grid h-full w-full grid-cols-1 overflow-hidden px-8 md:grid-cols-4\">\n          <img loading=\"lazy\" decoding=\"async\" width=\"250\" height=\"250\" src=\"\/wp-content\/uploads\/2024\/11\/Talullah-Blanco.png\" class=\"size-16 rounded-full md:size-32 col-span-1 md:ml-4\" alt=\"meet-experts-thumbnail\" srcset=\"\/wp-content\/uploads\/2024\/11\/Talullah-Blanco.png 250w, \/wp-content\/uploads\/2024\/11\/Talullah-Blanco-150x150.png 150w, \/wp-content\/uploads\/2024\/11\/Talullah-Blanco-56x56.png 56w, \/wp-content\/uploads\/2024\/11\/Talullah-Blanco-120x120.png 120w\" sizes=\"auto, (max-width: 346px) 260px, (max-width: 576px) 432px, (max-width: 720px) 540px, (min-width: 720px) 250px, 100vw\" fetchpriority=\"low\"\/>\n          <div class=\"col-span-3\">\n            <div class=\"my-4 flex-1 content-center font-circular text-lg font-medium text-slate-900 md:mt-0\">\n              Talullah Blanco            <\/div>\n\n            \n            <div class=\"text-slate-500 mt-2 leading-6\">\n              <p>Talullah Blanco is an insurance writer specializing in car maintenance, repair, and insurance. She leverages her experience as a storyteller to create useful, money-saving content for car owners. Since joining Jerry\u2019s team, Talullah has written over 600 articles on topics including license requirements, car insurance basics, and vehicle specs. Prior to joining Jerry, Talullah worked as a freelance writer contributing to lifestyle magazines and media websites, and as a fundraising coordinator.<\/p>            <\/div>\n          <\/div>\n        <\/div>\n\n        <div class=\"absolute hidden group-data-[expand=true]:flex bottom-0 w-full h-24 bg-gradient-to-t from-white from-30% to-transparent to-100% items-end justify-center\">\n          <div\n            class=\"flex cursor-pointer flex-row items-center gap-2 my-4 font-circular text-primary\"\n            data-wp-on-async--click=\"actions.onItemExpandClick\"\n          >\n            <span class=\"text-sm\">See more<\/span>\n            <span class=\"iconify i--chevron-down text-xs\"><\/span>\n          <\/div>\n        <\/div>\n      <\/div>\n      <\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>If you suspect your alternator is bad, you can disconnect the negative battery cable and use a voltage meter to test your alternator.<\/p>\n","protected":false},"author":19,"featured_media":64645,"menu_order":0,"comment_status":"closed","ping_status":"open","template":"single-advice","meta":{"jerry_authors":"[{\"id\":\"288\",\"type\":\"main-author\"}]","jerry_author_ids":[288],"jerry_idx_page_label":"","jerry_meta_desc":"If you suspect your alternator is bad, you can disconnect the negative battery cable and use a voltage meter to test your alternator.","jerry_related_posts":"[32969,6079,13254]","jerry_summary":"","inline_featured_image":false,"_lmt_disableupdate":"","_lmt_disable":"","footnotes":""},"categories":[],"tags":[116,120,621],"class_list":["post-4099","car-repair","type-car-repair","status-publish","has-post-thumbnail","hentry","tag-car-parts","tag-car-repair","tag-resource_car_repair"],"_links":{"self":[{"href":"https:\/\/jerry.ai\/wp-json\/wp\/v2\/car-repair\/4099","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/jerry.ai\/wp-json\/wp\/v2\/car-repair"}],"about":[{"href":"https:\/\/jerry.ai\/wp-json\/wp\/v2\/types\/car-repair"}],"author":[{"embeddable":true,"href":"https:\/\/jerry.ai\/wp-json\/wp\/v2\/users\/19"}],"replies":[{"embeddable":true,"href":"https:\/\/jerry.ai\/wp-json\/wp\/v2\/comments?post=4099"}],"version-history":[{"count":2,"href":"https:\/\/jerry.ai\/wp-json\/wp\/v2\/car-repair\/4099\/revisions"}],"predecessor-version":[{"id":64646,"href":"https:\/\/jerry.ai\/wp-json\/wp\/v2\/car-repair\/4099\/revisions\/64646"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/jerry.ai\/wp-json\/wp\/v2\/media\/64645"}],"wp:attachment":[{"href":"https:\/\/jerry.ai\/wp-json\/wp\/v2\/media?parent=4099"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/jerry.ai\/wp-json\/wp\/v2\/categories?post=4099"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/jerry.ai\/wp-json\/wp\/v2\/tags?post=4099"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}