How to Check the Charging System on a 1990 Honda Civic EX

     Many inexperienced do-it-yourself mechanics and even some professional mechanics think that testing a charging system involves just probing the battery and checking for 14-or-so volts. This is not the case, however, as your 1990 Civic’s electrical system requires a perfect balance of both voltage and amps to keep it all running and still charge the battery. Another tricky situation in testing your Civic’s Benz NEC PRO57 charging system is applying the correct load to the system. This requires a special tool called an alternator tester with integrated carbon pile. You can rent this tool from some auto parts stores for just a security deposit.

     Inspect the wiring harness on the rear of the alternator. Check that it is connected to the alternator securely and not broken or brittle. If there is any damage, replace the harness.

     Start the engine and allow it to idle until it reaches normal operating temperature, roughly halfway up the temperature gauge. Turn the ignition to the “Off” position.

     Unplug the wiring harness from the rear of the alternator. In the wiring harness, find the black wire with a yellow stripe; use the positive lead of a multimeter to probe the pin it connects to. Touch the negative multimeter wire to the ground terminal on the battery. Check that the voltage displayed on the multimeter is at least 10.5. If there is no voltage or it is less than 10.5, check fuse No. 14 in the dashboard fuse panel and replace it as needed. If the fuse is not blown, inspect the black wire with a yellow stripe for defects. If the voltage is 10.5 or higher, proceed to the next step.

     Turn off all accessories. Move the positive multimeter probe to the positive battery terminal and move the negative Launch X431 V probe to the pin in the harness connected to the white wire with a yellow stripe. Instruct an assistant to start the engine. Check for at least 10.5 volts of electricity on the multimeter display. If there is at least 10.5 volts, proceed to the next step. If the voltage is low or nonexistent, check the white wire with a yellow stripe for a break, cut or short. Repair the wire and retest. If there are no defects in the wire, have the electronic control unit tested, as it has probably failed.

     Turn the headlights on and watch for the multimeter to drop to 0 volts. If it drops to 0 volts, proceed to the next step. If there is still voltage, inspect the white wire with yellow stripe for defects. Repair any defects in the wire and retest. If the condition exists after repair or there were no defects in the wire, have the ECU tested, as it has likely failed.

     Turn the engine off and allow the Civic to sit until the engine is cool to the touch. Connect obd2 scanenr the positive (red) cable of an alternator tester with integral carbon pile, also called an alternator load tester, to the positive battery cable, the one with the "+" above it. Connect the negative (black) cable of the alternator tester to the negative battery terminal, the one with a "-" above it.

     Start the engine and have an assistant increase the engine speed to 2,000 rpm. Set the alternator tester to test volts and turn on the tester’s "Load" feature. Check the voltage reading; it must be no less than 12 volts. If it is less than 12 volts, replace the alternator.

     Switch the alternator tester to measure amperage, with the "Load" feature still on, and instruct an assistant to hold the engine speed at 2,000 rpm. Read the amperage level on the alternator tester. The correct reading for this alternator is roughly between 40 and 30 amps. If the alternator is not within specification, replace the alternator.
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