Component Tests and General Diagnostics

Basic checks


WARNING: Never start the engine while carrying out this test procedure, as the alternator could be irreparably damaged.


1 If the lamp fails to light up when the ignition is switched on, ground the 0+ terminal on the alternator while the ignition is still switched on.
2 It the lamp lights up, the electrical system is OK and the alternator is at fault.





Checking alternator output voltage
1 Connect a voltmeter across the battery terminals.
2 Run the engine at medium-high rpm for several minutes and read off the voltmeter.
A reading of about 13.5 - 14 V should be obtained.





Checking maximum alternator output power
1 Connect an ammeter to the alternator's output circuit (B+) or use a clip-on ammeter.
Run the engine at about 2500 rpm.
2 Apply a maximal electrical load to the alternator, either by connecting a special carbon film resistor to it or by switching on all the car's items of electrical equipment.
Read off the instrument.
3 The ammeter reading ought to be the same as the alternator's nominal rating:
2.0 liter 40 - 70 A
2.3 liter 45 - 90 A
V6 60 - 120 A





Checking the voltage drop at the positive and negative alternator terminals
1 Connector a voltmeter across the battery's positive terminal and terminal B+ on the alternator (insulated side).
2 Run the engine at 2500 rpm and apply an electrical load to the alternator by switching on all the lights, for instance.
Read off the instrument.
3 Connect a voltmeter across the battery's negative terminal and terminal B- (ground) on the alternator.
4 Run the engine at 2500 rpm and apply an electrical load to the alternator by switching on all the lights, for instance.
Read off the instrument.
5 The readings in points 2 and 4 should not exceed 0.5 V.
If a higher reading is obtained, check the relevant circuit for shorting/continuity