TOYOTA - MK2 MR2 - Alternator

Alternator Testing and Replacement

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The MR2 alternator isn't in a very accesible place. Although not much needs to be removed to get to it, it's a pain to remove and install. The alternator is located on the bottom side of the engine in the rear passenger side of the bay. It can be seen from above and below. I think you'll have the quickest removal and installation by accessing it from above.

Difficulty(0-5): 3
Time: 60-90 mins
Tool Simplicity(0-5): 3

Tools Required:

  • Sockets: 10mm, 12mm, (14mm)
  • Wrenches: 12mm, 14mm
  • Specialty: Multimeter (AC Votls, DC Volts)

01 Testing

An alternators job is to take energy from your motor (its crankshaft) and convert it to electrical energy to keep your car running and ensure the battery is sufficiently charged. When an alternator fails it can give you warning signs. The MR2 battery light will flicker when the charging system is having trouble. This could be a sign of a loose connection or outright alternator failure. Checking output voltage of the alternator and its “ripple” is a simple way to check alternator health.

Voltage Tests

DC Voltage: 13.9-15.1 VDC
AC Voltage: ~Less than 20-50 mVAC

Alternators can be tested by using an alternator tester found in most Auto stores. Most places can check this in the parking lot for free. If you want to check some things at home, you just need a multimeter. Using a multimeter set to DC voltage, place a probe on the positive and negative terminals. According to Toyota's service manual your results should be 13.9V-15.1V. A bad alternator can still output the correct DC Voltage so this isn't an all deciding test. If your results fall outside the range given it could be your alternator, wiring or your battery.

Now we need to check AC Voltage. The alternator creates AC voltage right from your drive belt. Your car’s electrical system doesn’t use AC voltage though, it uses DC Voltage. The alternator contains components that are responsible for this transition and a common cause of flashing battery indicators on the dash is that these components are on their way out. To check this, we set the multimeter to AC voltage.

The acceptable AC voltage or “Ripple” for a car’s system varies greatly from car to car and manufacturers don’t always seem to make the information readily available. For the SW2 MR2, I haven’t found a solid spec. I experienced 20-25 mVAC with my bad alternator and only 8 mVAC ripple with my good one.

Other Checks

  • Drive Belt - Ensure it is isntalled tightly and does not slip
  • Wiring - Ensure connectors and wires and installed and intact
  • Fuses - Check fuses and fusible links