"80% of warranty returns of starters and alternators can be avoided by employing a few simple battery and voltage drop tests."
-Bob Goulding, APRA Director of Training and Education.
Staying focused on the basics can save you time, comebacks, headaches and $$$! In reality, most starter and alternator problems are basic in nature and not that difficult to identify, yet all too often problems are approached by a kind of “trial and error” method. As stated in an excellent tech article in the November 2007 issue of Autopro Care News, according to both new and remanufactured rotating electrical suppliers, "more that half of their warranty returns have 'no fault found'." We have found the same thing to be true here at AIM. Approximately 75 percent of all warranty returns are either
not defective or are damaged from improper installation.
Like clogged arteries to the body, excessive voltage drop in any circuit spells trouble which means electrical devices that demand electrical power will be deprived and function poorly or not at all. The result is damaged components. If the starter for example is deprived of the power it was designed to function with, it will overheat and crank slowly or not at all. At the very least its service life will be cut short. The same is true with alternators; battery and wiring issues will cause premature failure.
With a typical “no start” scenario the complaint we often hear is "it just clicks" or "it's dragging" or "cranks slow, or not at all." Some would be quick to conclude that it must be a bad starter, but is it? Or you might even hear "we put another one on and its no better that the first one, its still doing the same thing" (Hmmm). In some cases, the replacement starter seemed to work for a while, maybe a week or two, and then gives out. This leaves the impression that the replacements were poor quality starters to begin with. And in those cases where the battery had been replaced along the way, that conclusion seems all the more firm.
Let’s get right to the point: Before changing any parts in the starting or charging system, the importance of proper diagnostics cannot be overstated. This might be compared to going to the doctor for chest pain and with little or no diagnosis you were told to take something for indigestion, only later to learn you had suffered a heart attack.
STEP -1 Get Input
As with any good doctor, good diagnosis starts with asking questions
about symptoms, and the sequence of events. Have the lights been left on requiring a jump-start? Was polarity observed in the process? Was the alternator used to charge up the battery instead of a charger? Does this vehicle sit for long periods, maybe coupled with short trips? How old is the battery? Answers to these and other questions are clues to mode of failure and add to the confidence of your tests. For example, if the owner tells you he used his other car to jump start a low battery, and then drove to work with the idea that his alternator would charge up the battery. Guess what? The alternator has been overheated and if he didn't kill it, he shortened its life. Of course if the charge light is on by now, this may very well be the reason.
STEP 2-Visual Inspection
Does it appear this vehicle has been maintained? Are cable connections to the battery, alternator and starter clean and tight, or do you notice even the slightest signs of corrosion or sulfation? Are there repair terminals on the cable ends? Even if they look okay, it is not uncommon to find poor connections where the end of the wire is clamped. Is the battery a little swollen on the sides? This is a sure sign that it needs replacement. It is also a good idea, at this time, to take a look at fuses and fusible links. If blown, ask yourself: Why? How about the condition of the alternator drive belt, could it be slipping? Is it glazed or cracked? Many vehicles now days have belt tensioners; is its spring weak causing excessive harmonics (vibration)? This can cause premature alternator bearing failure.
STEP 3- Check the Battery!!
According to one source,"62 percent of all starter failure and 67 percent of all alternator failure is due to a faulty or weak battery." Both the starting and charging systems depend on the battery; this is where it all starts. The first objective is to verify its condition, state of charge and capacity. Its state of charge can quickly be checked with a voltmeter and should read a full 12.6 volts. It is sometimes assumed that anything over 12 volts is good enough. NOT SO! Keep in mind that every .2 volt under represents a 25 percent loss in capacity!! At 12.4 volts it must be recharged.
Verify its condition with a load test (only after it is charged) with a good battery tester. The capacity--that is its CCA (Cold Cranking Amps) rating--can be compared to the minimum requirements published in Battery Supplier catalogs.
STEP 4- Voltage Drop Testing
Once it is known that the battery is up to the task, we now want to confirm the condition of wiring and connections. In the case of the alternator, is its power being efficiently transmitted to the loads - the battery and vehicle electrical systems? And in the case of the starting system, is there sufficient power to operate the solenoid or relay, or the starter motor itself to crank at full rpm? It is truly amazing how often poor connections are overlooked because they appear okay but appearances can be deceiving! Actually, voltage drop testing is the only way to know for sure if there are power losses (voltage drops), in high amp circuits.
As a rule of thumb, in low current circuits, such as the smaller wires to the regulator you don't want to see more that .1V (one tenth of a volt). On high current circuits, such as power to the starter, .5V (one half of a volt) max where there is a solenoid or relay involved - on the 'hot' side, and .3V (three tenths of a volt) on the negative or ground side. On the alternator output circuit, expect .2V on both positive and negative sides of the circuit. Bear in mind, the ground side is every bit as important as the positive side of the circuit, and that voltage drop tests must be done with the circuit under full load; that is current must be flowing. The following illustrations show some of the basic yet effective means for isolating the most common wiring issues in charging and starting systems.
The Charging System
With engine at 2500 rpm and charging system loaded using a carbon pile (or by turning everything on), check the following:
1. Check for voltage drop on the Positive Output Side
-Illus. 1
2. Check for voltage drop on the Ground Side
–Illus. 2
3. If the alternator is suspected of not turning on, check for power to the excite terminal of regulator – With key on, check as illustrated:
-Illus. 3 for Standard Lamp
-Illus. 4 for PCM lamp control: A reference voltage of only 4 – 5 volts is expected
Note: Most late model vehicles the lamp is controlled by the PCM (onboard computer). Because of very low current, with some as low as 10mA, there can be no voltage drop.
4. If a failed regulator is suspected, or the system voltage is too high and/or the alternator is not charging check for voltage drop to the ‘Sense’ terminal of the regulator (marked ‘S’ on most vehicles, ‘A’ on Ford)
-Illus. 5
Note: High resistance here can kill the regulator.
The Starting System
Disable ignition and perform the following tests while cranking:
1. Check for voltage drop on the Positive Side
-Illus 6
-Illus 7
2. Check for voltage drop on the Ground Side
-Illus 8
3. Check for voltage drop to Starter Solenoid
-Illus 9
4. Check for voltage drop to Starter Relay, if equipped
-Illus 10
