Diagnosing Starters & Alternators

The starter and the alternator are two essential rotating electrical systems in each vehicle. Over time they have not changed much except that they have gotten smaller, and especially on the alternator side, they are asked to do more.
No internal combustion vehicle can operate without these two systems working at peak performance. Art French, the owner of AML Auto Service, has been in the auto service game for nearly 40 years. He said that alternators and starters rarely give a warning before failing. “Generally, they just fail,” he said. “In my experience, it is usually the alternator wearing out, because they will wear out over time. There are brushes in them, there are electrical contacts there. These will wear out over time. Starters just generally go all of a sudden.”
The difficulty with diagnosing a dying alternator can be seen on a video at the SSGM Web site where Technical Editor Jim Anderton replaces an alternator on a Ford 150 pickup truck. (http://www.ssgm.com/videos/play/?plid=1000402606) The alternator is “howling like a banshee,” as he puts it but still putting out proper voltage. In this case the problem was audible – this is rarely the case.
The best maintenance is preventative maintenance and as a shop owner you and the technicians should be testing the alternators and starters on a regular basis. “Before the rotating electrical units fail, routine preventive maintenance that includes replacing leaking hoses or seals, and replacing weak batteries and checking for loose connections or corrosion may help prevent some failures,” said Kevin Brimble the Network and Marketing Manager for ACDelco. “Some failures do occur without any warning.”
The heart of any vehicles electrical system is the battery and that should be checked first, before any attempt of repair is made. “Battery testing is also an important component of checking alternators and starters,” said Dean Ferri, the Diagnostics District Sales Manager for Robert Bosch Inc. “A sulfated battery can cause an alternator to ‘work harder’ which will shorten the lifespan. A battery with a lower capacity will have a lower voltage during cranking which can increase current demand from starter and shorten lifespan.”
French said, “We try to keep on top of battery testing. A weak battery over-stresses the alternator and can result in the premature failure of the alternator. We can put a load on them to make sure they give out the proper amperage – to what it is supposed to be. We will test them as part of regular maintenance,” he added. “Usually, when we get them in, it is not to see if it is on the way out. It usually is, and if there is a failure we replace it.”
A wise thing to do when servicing the alternator or starter is to check for any and all error codes in the vehicle before disconnecting the battery. Disconnecting the battery wipes out any codes that might have been stored in the vehicle’s ECM and doing a simple scan will alert you to any potential problems that might exist with the vehicle in question. If you repair the alternator or starter and there is an undiagnosed problem that the customer experiences after they pull away from your shop – they will blame the shop for that problem and you will have an unhappy customer on your hands.
“Alternator can be checked with equipment like the Bosch BAT 151 or even a scope to check for alternator ripple that can indicate a bad diode,” said Ferri. “An alternator can still be charging, but at a reduced capacity before it fails completely. Starter current draw is also a good indicator of starter health. Most of the time, starters do not fail overnight, but a customer may not notice a slightly slower cranking RPM. A complete battery / starter / charging test can find these issues before the cars quits. Also, for both alternators and starters, it is critical that there is no voltage drop in the cabling leading to those devices. Ferri pointed out that with the complex electronics in today’s vehicles sometimes it is not the starter that has failed when the car will not turn over. “In most newer vehicles, the ignition switch is not connected directly to the starter, the ECM controls a relay to start the vehicle. Issues with theft, brake light switches, etc. can all prevent a starter from engaging when requested.
The complexity of the systems can also on occasion lead to a failure of the alternator’s or starter’s clutch pulley system. “When clutch type pulleys fail on an alternator the usual complaint is noise or a no charge condition if the drive belt is compromised,” said ACDelco’s Brimble. “On starters, when a drive clutch assembly fails, a no-start condition occurs.” Fred Padgett the North American product manager – Rotating Machines for Robert Bosch Inc. said, “If the belt tensioner, or the clutch pulley mechanism fail prematurely, then undue stress can be placed upon the bearings in the alternator specifically the front bearings creating a failure of the bearing. In today’s world with serpentine belts, the angle of deflection, or amount of ‘misalignment’ that is permissible or acceptable is next to nothing. In most cases, if an installer has to remove and install a serpentine belt on an engine for any reason, and does not get the belt lined up correctly, the belt will usually come off the pulley, or shred itself in a very, very short time. Most of the time, this belt failure would occur before any damage to the alternator would occur. In older style alternators that utilized V belt pulley systems instead or wider serpentine belts, it was possible to have belts misaligned, and have them keep running on the vehicle. Over time, this would cause damage to the bearings in the alternator.”
Art French from AML Auto Service said that alternators and starters seem to last longer now and do not fail as often.
“In new alternators, Bosch does a tremendous amount of testing in the preliminary engineering stages of a rotating electrical product, to ensure that the design and components can meet or exceed the vehicle manufactures’ specifications,” said Padgett. “This testing, includes but is not limited to, salt spray testing, vibration testing, thermal shock testing, life testing both on benches and on vehicles. When Bosch analyzes a new design of alternator or starter the engineers look at parameters called B10 and B50. Essentially what these terms mean is that if we are talking about B10 this means that out of a certain batch of parts, 10 per cent of them will fail at a certain point in time, either in mileage or hours of use, and 90 per cent of them will show no signs of failure. B50 Means that 50 per cent of the product will have failed and 50 per cent will have no signs of failure. B10 is the most commonly looked at parameter, and the Bosch starters and alternators are designed so that the B10 rating is greater than the expected life of the vehicle.”
With remanufactured alternators and starters being what is usually installed in a repair, these parts share the same rigorous standards as new parts. “ACDelco’s remanufactured rotating electrical products utilize ISA approved replacement parts that must meet minimum performance criteria and must meet a minimum of durability testing hours for alternators or test cycles for starters,” said Brimble.