Foreign Service

Foreign Service Dan describes the tools and techniques necessary for an accurate diagnosis of the ‘half-Monty’ charging system found on some recent Kia and Mazda vehicles.

Dan Marinucci

L

ittle Stevie, a talented technician I know, has a knack for offbeat description. For instance, I was explaining that Chrysler began moving its voltage regulator inside the ECM back in the 1980s. For some reason, Stevie dubbed this technique a “full Monty.” If moving an entire regulator inside the ECM is a full Monty, then this month’s column concerns the “half-Monty” in some Kia and Mazda cars. Yes sir, they put half the voltage regulator in the alternator, the other half inside the computer. Here are the key things you should know about testing a half-Monty. The parts catalogs tell us the half-Monty charging system appears on the 1997 Kia Sephia and 1997-2001 Mazda Protegés. The Sephia has a Hitachi alternator and the Protegé uses a Mitsubishi, but electrically, the two units work the same way. Both alternators use the same connector shown in photo 1 below, which contains terminals P (phase) and D (driver). For this reason, some auto-electric specialists call the half-Monty the “P-D”

1

D

Photos & screen captures: Dan Marinucci

P

charging system. I’ll get back to the P-D terminals in a moment, but first we need a bit of review. The heart of the alternator is the field circuit, which contains the voltage regulator and the rotor. When the voltage regulator’s power transistor switches on the rotor, the alternator charges. Turn off the rotor and it stops charging. On the vast majority of vehicles you service, the entire voltage regulator is mounted inside the alternator. But on the half-Monty Hitachi/Mitsubishi, the power transistor assembly is the only part of the voltage regulator left inside the alternator. It’s now called a field control unit because all it does is switch the rotor on and off. Terminal D goes to the base of this power transistor. The ECM or PCM controls the rotor— and, therefore, alternator output—by controlling terminal D. The left-hand screen capture on the top of page 14 shows a typical PCM-to-driver signal at idle with no accessories operating. Because there’s no significant electrical load, the PCM pulses the field circuit on and off. Compare that to the screen capture on the right, which is the PCM-to-driver signal when all the car’s accessories are operating. No pulsing here! Instead, the PCM reacts to the heavy electrical demand with a steady voltage signal that holds the field circuit full on. I’ll emphasize two things about terminal D before we proceed. First, if the PCM doesn’t signal or “drive” terminal D, this half-Monty alternator won’t Monty at all. So if the unit won’t charge, remember to scope the “drive” circuit at the alternator and again at the PCM. When a computer won’t produce the PCM-toD signal, check all wiring and connections before condemning the computer itself. Second, note that the PCM-to-driver signal is less than 1.50 volts. Never jumper battery voltage directly to terminal D or you’ll toast the field control unit! In previous columns, I’ve cited information

continued on page 14

12

May 2002

Foreign Service

from JIMCO, Inc., a Raymore, Missouri, company that makes starter/alternator test benches and related electrical goodies. According to JIMCO’s John Grube, the P terminal is a convenient diagnostic tool for both you and the PCM. The voltage at P, which represents one phase of the stator, should be one-half charging voltage (plus or minus about .50) on any healthy alternator. So if the alternator is producing 14.00 volts, P should be 7.00 volts. Note that a phase terminal is not available on all alternators. Grube urges you to do what all

2

14

May 2002

good auto-electric technicians do: Make P voltage measurements another part of your diagnostic routine. For example, an open positive diode increases P voltage by about 1.50 volts. An open negative diode decreases P voltage by about 1.50 volts. An open stator “leg” or phase decreases P by about 1.00 volt, he told me. Traditionally, the voltage regulator inside the alternator handled two chores: It sensed battery voltage directly—often through a terminal labeled S—and it controlled the charge indicator light. But on the Kia and Mazda half-Monty, the PCM controls the indicator light and battery voltage is one of the computer’s important inputs. According to Grube, the PCM is constantly monitoring and comparing battery voltage with P terminal voltage. Then it turns on the indicator light when these voltage readings suggest trouble. The beauty of the system, Grube says, is that it’s equipped to make better decisions and sense

charging system problems more accurately than a conventional voltage regulator can. So the bottom line on Kia’s and Mazda’s half-Monty system is that you can apply all the routine charging system tests to it; it just requires some additional checks—first, the digital voltmeter check on terminal P and the PCM’s battery voltage input; second, a scope check of terminal D. Last but not least, you can use JIMCO’s I-60 to quickly and accurately isolate the P-D alternator from the PCM. The I-60, which we covered in this column almost three years ago, is the compact test kit shown in photo 2 on this page. A wide range of vehicle-specific adapters enable an I-60 user to bypass all vehicle wiring (save the alternator output wire) on 90% of the cars and light trucks you service. If you bypass the vehicle wiring with this kit and the alternator works normally, you know the problem is outside the alternator. The I-60 adapter shown on top of the alternator in photo 2 contains electronics that duplicate the PCMalternator relationship described earlier. When you connect it, the field control unit thinks it’s connected to a good computer. Cool? If you want additional information on the I-60 charging system test kit, contact JIMCO at 800-821-7137 or [email protected].