Honda Charging Systems COLUMN BY JOHN THORNTON You are investi- gating an apparent no-charge condition on an early 1990s 4 « Accord. Engine run- 2 ning voltage is approximately 12.5 volts. You notice the green, round plug on the back of the alternator is the four terminal design. “Ah-ha! The engine computer has something to do with charging,’ you say to yourself. Also, you remember these cars have a device called an electronic load detector (ELD). This item may also affect the charging system. Determining if a late model Honda alternator is properly charging is usually not difficult. What can be difficult, or at least challenging, is the failure diagnosis. By failure diagnosis, I mean providing an answer to the following question: Why isn’t the alternator charging? We all have our own technique or style for handling charging system diag- nosis, developed over the years through our various diagnostic experiences. In my case, some of these experiences have cost me time and money. The purpose of this article is to share with you some of the techniques I use to evaluate late model Honda charging systems with a computer interface, focusing on: the computer interface, wiring up to the alternator, and the ELD. Hopefully the tests I suggest will enhance you and your customers’ diagnostic procedures (and save you time and money). Let’s start by defining the particular system we will be discussing. In 1988, Honda introduced their second genera- tion charging system with a computer interface. I hesitate to call this system computer controlled. Granted, the com- puter does have the ability to reduce charging voltage; however, the engine computer does not control or manage the field circuit. An example of a true computer controlled charging system is the Chrysler charging system in which the voltage regulator is in the power module, SMEC or SBEC (depending on the year). The Honda system is similar to a GM CS series alternator that may be connected (interfaced) to a BCM (body control module). The BCM can measure charging voltage and field cir- cuit on-time, and can turn the voltage regulator off under certain conditions. Honda’s first brush with a computer interface debuted in 1984 on the CRX. This system is different from the one we’ ll be concentrating on. However, it’s beneficial to briefly review this first generation system so we are aware of the differences and similarities. You are probably very familiar with the precau- tion surrounding this particular charging system: under certain conditions, the alternator may not produce charging voltage. This delay can last for approxi- mately 60 seconds. Let me quote the 1986 Honda CRX shop manual. The alternator control unit senses changes in engine load and controls the alternator to compensate for those changes. In other words, the control unit varies the rate of charge depending on driving conditions. For instance, the alternator control unit will signal the alternator to deliver a_ higher voltage output (14.5 volts) during deceleration or braking, but only nor- mal output voltage (12.5 volts) under most other circumstances. Alternator operation (charging volt- age) can be limited under certain conditions by design. This was done to decrease engine load and increase vehicle mileage. While watching charg- ing voltage in the shop, it sometimes appears the alternator is “off’ more than it is “on.” This alternator can be identified by the three terminals in its plug: ¢ L (lamp): white with blue tracer wire controls lamp operation and can pro- vide power to the choke heater. °IG (ignition): black with yellow tracer wire is the ignition feed for turn-on. ¢C (computer): white with yellow tracer wire is the interface from the alternator control unit; the alterna- tor control unit is a separate module from the emission control unit (engine computer). When the alternator control unit grounds the C circuit, charging voltage will decrease to approximately 12.5 volts. Ungrounded, the alternator will perform normally. There are a number of inputs to the alternator control unit that can increase charging voltage. The most well known and probably easiest to activate is the brake switch input. Depressing the brake pedal causes the alternator control unit to remove the ground from the C circuit, which in turn causes charging voltage to increase. Please remember, it’s not unusual for this first generation system to operate at 12.5 volts at idle if there are no elec- trical loads on the system. Let’s get back to this second genera- tion system. This alternator (Mitsubishi or Nippondenso) can be identified by its four terminals, round regulator plug. The four terminals are identified as follows: ¢L (lamp): circuit controls warning lamp operation °IG (ignition): circuit provides the ignition feed for turn-on ¢ C (computer): circuit is the interface from the programmed fuel injection control unit (engine computer) ¢ FR (field monitor): circuit provides feedback information to the engine compu