Diagnosis & Testing
- Turn off all lamps and electrical components.
- Place the vehicle in transmission range NEUTRAL and apply the parking brake.
- Carry out the Load Test and No-Load Test according to the following component tests:
- Switch the tester to the ammeter function.
- Connect the positive and negative leads of the tester to the corresponding battery terminals.
- Connect the current probe to the generator B+ output terminal, circuit 38 (BK/OG).
With the engine running at 2,000 rpm, adjust the tester load bank to determine the output of the generator. Generator output should be at least 87 amps.
- With the engine running, turn the A/C on, the blower motor on high speed and the headlamps on high beam.
- Increase the engine speed to approximately 2,000 rpm. The voltage should increase a minimum of 0.5 volt above the base voltage.
- If the voltage does not increase as specified, carry out the No-Load Test in this section.
- If the voltage increases as specified, the charging system is operating normally.
- With the engine running, turn on the blower motor and the high beams ( or other electrical accessories to place a load on the charging system).
- Increase and hold engine speed to 2000 rpm.
- Measure the voltage reading at the battery.
- The voltage should increase at least 0.5 volts from the voltage test. If the voltage does not meet specifications, the charging system is malfunctioning.
Alternator No-Load Test
- Switch the tester to the voltmeter function.
- Connect the voltmeter positive lead to the generator B+ terminal and the negative lead to ground.
- Turn all electrical accessories off.
- With the engine running at 2,000 rpm, check the generator output voltage. The voltage should be between 13.0 and 15.0 volts.
- Connect a tachometer to the engine.
- Turn off all electrical loads (radio, blower motor, wipers, etc.)
- Start the engine and increase engine speed to approximately 1500 rpm.
- Measure the voltage reading at the battery with the engine holding a steady 1500 rpm. Voltage should have raised at least 0.5 volts, but no more than 2.5 volts.
- If the voltage does not go up more than 0.5 volts, the alternator is not charging. If the voltage goes up more than 2.5 volts, the alternator is overcharging.
- If the voltage is within specifications, proceed to the next test.
- Make sure the engine is OFF , and turn the headlights on for 15-20 seconds to remove any surface charge from the battery.
- Using a DVOM set to volts DC, probe across the battery terminals.
- Measure the battery voltage.
- Write down the voltage reading and proceed to the next test.
Several precautions must be observed when performing work on alternator equipment.
Removal & Installation
- Before servicing the vehicle, refer to the Precautions section.
Remove or disconnect the following:
Negative battery cable
Install or connect the following:
Alternator. Tighten the bolts to 15-22 ft. lbs. (20-30 Nm).
- Disconnect the negative battery cable.
- Tag and disconnect the wiring connectors from the rear (or side) of the alternator. To disconnect push-on type terminals, depress the lock tab and pull straight off.
- On 3.8L and 4.6L engines, rotate the automatic tensioner away from the drive belt and disengage the drive belt from the alternator pulley. Remove the alternator brace.
- On 3.8L engines, remove the alternator pivot bolts, top and bottom and remove the alternator.
- On 5.0L engines, loosen the alternator pivot bolt and remove the adjusting bolt. Disengage the drive belt from the alternator pulley.
- On 3.8L and 5.0L engines, remove the alternator pivot bolt and the alternator. On 4.6L engines, remove the alternator mounting bolts and remove the alternator.
- Installation is the reverse of the removal procedure. On 4.6L engines, tighten the alternator mounting bolts to 15-22 ft. lbs. (20-30 Nm) and the alternator brace bolts to 70-106 inch lbs. (8-12 Nm). In addition, on 5.0L engines, adjust the drive belt tension (refer to Section 1).