Honda uses a dual-mode charging system on most 1990-2012 applications (figure 3). This system decreases drag on the engine while cranking and reduces charging system output (engine load) for improved fuel economy. Similar to other systems, the PCM controls the alternator. The PCM receives the system voltage and amperage demand from the electronic load detector in the fusebox.
Cranking (Low Output Mode) — during cranking, the PCM will set the output target between 12.4-12.9 volts. This mode will be active when the system meets a given set of criteria, leading the PCM to command the alternator to reduce the charging system output. Don’t misinterpret low output mode as a bad alternator.
Normal Mode — with the engine running and a specific set of criteria met, the PCM will command a target output voltage between 13.5 and 14.9 volts. With the ignition switch on, the alternator should receive a signal on the IG circuit greater than 12 volts, which it uses to activate the alternator.
PIN C — the PCM looks at the alternator PIN C to determine voltage output. With the circuit grounded, the alternator will be in low output mode.
PIN FR — The PCM supplies a 5-volt signal to PIN FR. The alternator regulator toggles the circuit to ground the varying duty cycle based on alternator load.
PIN IG — Ignition
PIN C — Computer; when output is demand is low, the PCM will ground PIN C, forcing the regulator into low output mode.
Starting in 2013, Honda introduced an updated design that uses a single control wire.
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