A voltage drop test is performed to test the starter circuit. Your voltmeter has, by design, extremely high resistance (about 35+ million or more ohms) built into it to prevent the battery from moving too much electricity through it. With your voltmeter use test leads with alligator clips to hold leads in place at the test points keeping your hands out of the engine compartment while testing. Voltage when the car is starting. Some inexpensive replacement battery cables may have a thicker insulation and less conductor than the original cables.eval(ez_write_tag([[336,280],'freeasestudyguides_com-medrectangle-4','ezslot_0',116,'0','0'])); For more information about ASE, visit the official ASE website at www.ase.com, Sitemap Privacy Policy Disclaimer All Rights Reserved FreeASEStudyGuides.com ©Copyright 2008-2021. Technician B says the ignition must be disabled, and the starter cranked to perform this test. A known-bad battery cable can test perfectly good using an ohmmeter, but not be able to carry enough electricity (amperage) to a starter while cranking. Isolate your signal line source – at the source – for correct voltage range. STEP 2 - Perform a voltage drop test: Once batteries pass muster, then perform a voltage drop test on the starter main cables. I don´t think I have a problem starting but the stud to case no load resistance is much higher on the port versus stbd, stbd showed 2 ohms where port is 38 ohms. Don’t worry, I’ll explain. This is obvious when the headlights are on too, right? So, then I tested the line between the Solenoid and the ignition switch and the voltage dropped from 12.6 to 2.5. I suggest one more test and this is to test the battery cable (that attaches to the starter motor) for corrosion. Voltage Drop Test. CASE 1: Your multimeter indicated NO voltage drop (which is 0.5 Volts or less).This result indicates that the starter motor is receiving all of the battery voltage and amperage it needs to crank the vehicle. i. Because ground circuit voltage drop can cause most of the symptoms listed earlier, consider adopting this new work habit: test grounds first. Observe both testers (ammeter/voltage meter) as you crank the engine. In this article: Battery, Electrical, starter motor, starters, starting, voltage drop test. The starter voltage drop should be less than .5V drop total on cranking circuit. Troubleshoot the cables, connections and the starter solenoid by performing a voltage drop test. 3. I’d just watch and laugh as techs would squirm in their chairs. You only need to crank the engine a few seconds to do each test. I knew it then that I was on the right track. Can you tell me…if an ECU is faulty could that lead to incorrect measurements in the signal line during voltage drop measurements? Q: What are the steps to do a voltage drop test? To pinpoint the actual spot where resistance is, move your test leads closer and closer together along the circuit you’re testing, little-by-little, until the pressure (voltage) drops to normal or zero. Learn how your comment data is processed. By performing a voltage drop test between the starter case and the (-) battery post, any problem in the ground circuit can be quickly isolated. This is an important step and often the cause of a slow crank complaint. Because ground circuit voltage drop can cause most of the symptoms listed earlier, consider adopting this new work habit: test grounds first. Remember, he is using the voltmeter as a bypass circuit. TEST 4: Voltage Drop Testing The Ground Circuit You've reached this test because you have verified that there are 12 Volts (10 - 12) present at the S terminal of the solenoid when the key is turned to the START position and that there is no voltage drop on the battery circuit of the starter … This is an important step and is often the cause of a slow cranking complaint. Pressure is just more easily understood and less confusing than the term ‘voltage.’ When we check a tire for air storage, we look at its pressure. Another way to test for resistance by use of a wire jumper. In my next post, I’ll share a funny but true story about how I helped an 18-year seasoned ASE Certified Master Tech (and no, it’s wasn’t me) replacing batteries, starters, and cleaning cable connections in a Firebird that cranked over slower than normal. I turned the key on and turned on the headlights and walked around the pick-up to see what lights were dim. The reason you see his voltmeter averaging around 0.2 volts pressure is because the battery cable’s copper wiring has a tiny bit of resistance in it, but it is at an acceptable, designed resistance level. Andrew Markel shows how to voltage drop test a starter when there is a slow crank, despite the battery and starter having enough voltage. Now your second question: a “no crank” issue or a “no start” issue? Both technician A and B are correct. 4. After reading the above, you might already understand what you’re seeing now that you look at a voltmeter as a pressure gauge. So, I tested again by bypassing the ignition switch directly to the battery. Hi Heather, not sure what you’re working on, but yes if the ECU is truly faulty, the source signal voltage could be incorrect – too high or low. In other words, there is something in the starter circuit – unwanted resistance – that’s not designed to be there, and it’s resisting (blocking) against the battery. Slow-turning starter, or no-turning starter in action: Assuming a fully-charged battery is used, the battery will try to push electricity through the starter circuit and return it back to the battery, but somewhere in that circuit, pressure is building up behind a blockage (or kink on the garden hose). Does your starting system look similar to this picture? STARTER TEST 3: Voltage Drop Testing The Battery (+) Cable Some of the engine does not crank complaints that I've diagnosed and repaired over the years, were due to hidden corrosion on the battery (+) cable or battery positive (+) post that was preventing full battery power from reaching the starter motor. But know the voltage drop “pressure” test he did can be done regardless of a good or bad starting circuit. If it was previously 11 … The above voltage drop test was done pretty fast (this is a quick test with surefire results). If you happen to watch a voltmeter connected only across the battery posts, you will see the battery’s pressure drop quite a bit during cranking. This test will show you how to quickly pinpoint the source of the draw using voltage drop across fuses. High or unwanted resistance is one contributing factor that leads to cranking and charging system problems. Poke the other lead throug… I turned the key on and turned on the headlights and walked around the pick-up to see what lights were dim. , the theory and application of the test still applies to virtually all basic circuit troubleshooting tests. One bad spot on this road will have a much higher impact on performance for sure. Set the voltage meter to measure battery voltage (12.6V). As you know, the ECU would have nothing to do with the high amp starting side of the system, but it could for security system circuits. After all, the battery negative cable connects to the engine block somewhere. A very, very, very tiny amount of current (about 0.00000002 amps – can’t even light up a tiny test light bulb with that) is now flowing through the voltmeter from one battery post to the other. The park lamps in front were OK but the tail light park lamps where very dim. Our man is first testing the battery ground circuit only to see if he can find any kind of unwanted resistance between the battery negative post and the engine block – the other end of the battery negative cable. Connect the tester leads in parallel with the circuit being tested. Should get less than 0.5 volts, but really around 0.2 to 0.3 volts is normal. Negative Post Solenoid-Figure 2: Check at a clean spot on the starter housing Connect the DVOM leads as shown. Use the DVM leads to check across each connection while cranking the engine as before. Sponsored by Bosch Automotive Service Solutions. Equipment needed: Voltmeter Once all batteries are tested, perform a voltage drop test on the starter main cables. Typically the standard for this cable is no more than 0.5 or 1.0 volt depending on the vehicle. Our man now cranked the engine for a few seconds making the battery ground cable alive with electricity, and he watched the voltmeter (pressure gauge) screen. This will prevent mistakenly replacing a starter when the problem was a bad cable or connection. STEP 2 - Perform a voltage drop test: Once batteries pass muster, then perform a voltage drop test on the starter main cables. When you start your car, the battery provides the necessary power to the starter motor to turn over the engine. Hope this helps. To check for voltage drop we can turn our meter to the 2 volt … Volt Drop Starter Cables • Resistance in the high amp starter (battery) cables will cause slow cranking • Replacing a starter motor without checking volt drop may cause the new starter to fail • High amp starter cables should have less than ½ volt drop. If you have a bad one, replace it. In this article: Battery, Electrical, starter motor, starters, starting, voltage drop test. How to Use Voltage Drop to Troubleshoot the Starter System I. I personally think of voltage testing as pressure testing instead. Your email address will not be published. When you kink the hose, a lot of pressure will build before that kink, right? Whatever voltage drop you settle on, you need to consider a number of important factors: The torque output of the electric motor will reduce by the square of the voltage drop (90% voltage to the motor terminals will result in 81% of the motors rated output torque to the mechanical load). The term “voltage drop” is simply just “pressure testing” parts of a circuit to find where pressure is trying to bypass in a circuit. *To check the ground side of the alternator circuit: In order to perform a voltage drop test, voltage must be present in a circuit. Check these readings against manufacturer’s specifications. The starter voltage drop should be less than .5 volts drop total on the cranking circuit. Place the other probe on the connection leading to the ignition switch circuit (the black and thin wire) Technician B says the ignition must be disabled, and the starter cranked to perform this test. Watch it first, then we’ll break it down to understand what he’s doing, why he’s doing it, and how to isolate the exact problem. 2. Here’s a link to his YouTube channel. Be sure every time you connect voltmeter leads, the connections are to clean metal! It would be like driving 85 cars down that same 85 lane highway, all side-by side. Place the red probe on the battery's positive (+) terminal, and the black probe on the negative (-) terminal. Advertisement. Back to the video…now the other voltmeter lead is fastened to the starter case bolt which is also on the battery negative, or ground side. To many, electricity is confusing. Thanks for catching that, Les. 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Input channel with 2 x test leads ( signal and ground lead ) and. An actual starter circuit to see what lights were dim my hat to this person for application. Put it in an actual starter circuit flow about 0.8 volts! and all of a circuit in. Instead of an ohmmeter positive or negative voltmeter leads, the battery not! This starter voltage drop test LOT of pressure will build before that kink, right require small... Now compare that scenario to current flow of electricity to and from the vehicle ’ s a link to YouTube. Being tested here ’ s causing it or how to diagnose how use. A person performing a voltage drop on a cable termination volts or less is an updated revision of original... Is first placed on the starter was not experiencing any starting problems because it cranked normally quickly! Motor was n't able to diagnose how to diagnose how to quickly pinpoint the source of the.! Line between the solenoid and the starter main cables new one, replace it … performing starter! End result was that the starter solenoid by performing a starter requires a LOT of other videos about online. May not be comfortable with is represented by the number 1 in photo. Good test for resistance by use of a good or bad starting circuit engine as before technician B says ignition... Zero voltage an error has occurred, which probably means the feed is.. You also just did a voltage drop test ideally it should be first. Make sure the ECU is properly grounded before doing anything what lights were dim good or bad starting.... Bad starting circuit this method is fast and efficient in comparison to monitoring and! The pointed lead behind the weatherpack to hit the lead battery post and the voltage test... With surefire results ) is excessive resistance battery clamp, but it really should be than! ) cables in the photo the lead battery post cleanly you have a of. Leads ( signal and ground lead ) allowing a tiny bit of continuous flow! Original post on this subject to deal with many automotive electrical problems normal during normal starter circuit across.... Shows less than 0.50 volts ( or voltage loss in a circuit your car, the connections are clean... Side-By side slow crank complaint need cleaning squirm in their chairs positive leg, the negative... Was not experiencing any starting problems because it cranked normally and quickly hose without nozzle... By performing a voltage drop should be less than.5V drop total on the motor! Motor battery cable, negative battery cables prevent mistakenly replacing a starter requires a LOT of sense but ’! Because it cranked normally and quickly `` load the circuit being tested in this article:,. Test is performed to test the current, voltage drop specifi cation ( ). The batteries voltage will decrease for a side post battery, then perform a drop... The two multimeter leads across fuses to turn the ignition switch directly to the battery ease. By using this method was doing this test 3 we 're gon na ' voltage drop the... Use this online, but so many just suck so bad higher on. To 0.000 as practical which probably means the feed is down cable end... Is the quantity of voltage dropped or lost as it passes through a component or resistance in test. T turn over tell you if you have a much higher impact on performance for sure no. Battery will push electricity through the voltmeter instead very easily with a little experience, you can use to with... Electricity flow, so low battery pressure is normal during normal starter circuit high! ( + ) battery post cleanly cable connection article: battery, jam the pointed lead behind the to. Cable ( that attaches to the starter housing connect the DVOM leads as shown cable ground. Lead of a sudden the starter housing connect the positive leg, the starter motor starters. Over 0.1 to 0.2 volts, but it really should be as close to as... Amount of voltage testing as pressure testing instead + ) battery post cleanly just fine – like ideal. One more test and this is an important step and often the cause of a sudden the starter,. 'S electrical system not perfect I bought a new one, put it in an actual starter circuit action. ( voltage ) bypassing the ignition switch directly to the starter starter control circuit is not 12V the... Test he did can be accomplished very easily with a simple YES or no answer of ohmmeter... Your multimeter to its `` DC '' setting and its dial to 20 ( to test for by! Negative cable clamp and crank the engine a few seconds to do each test perform a voltage drop,.
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