Current Output Tests

The current output test will determine if the charging system can deliver its minimum test current (amperage) output. Refer to the Specifications for minimum test current (amperage) requirements.

The first part of this test (Test 1) will determine the combined amperage output of both the generator and the Electronic Voltage Regulator (EVR) circuitry. The second part of this test (Test 2) will determine only generator amperage and will not include analysis of EVR circuitry. EVR circuitry is located within the Powertrain Control Module (PCM). To test voltage regulator circuitry refer to the appropriate Powertrain Diagnostic Procedures.

Preparation
1. Determine if any Diagnostic Trouble Codes (DTC's) exist. To determine a DTC, refer to On-Board Diagnostics. For repair, refer to the appropriate Powertrain Diagnostic Procedures.
2. Before starting test, make sure battery is in good condition and is fully-charged. See Battery for more information.
3. Check condition of battery cables at battery. Clean if necessary.
4. Perform the previous Charging System Resistance Tests (voltage drop tests). This will ensure clean and tight generator/battery electrical connections.
5. Be sure the generator drive belt is properly tensioned.
6. A volt/amp tester equipped with both a battery load control (carbon pile rheostat) and an inductive-type pickup clamp (ammeter probe) will be used for this test. Refer to operating instructions supplied with tester. When using a tester equipped with an inductive-type clamp, removal of wiring at the generator will not be necessary.
7. Start the engine and allow it to reach operating temperature.
8. Shut engine off.
9. Turn off all electrical accessories and all vehicle lighting.
10. Connect the volt/amp tester leads to the battery. Be sure the carbon pile rheostat control is in the OPEN or OFF position before connecting leads. See Load Test in Battery for more information. Also refer to the operating instructions supplied with test equipment.
11. Connect the inductive clamp (ammeter probe). Refer to the operating instructions supplied with test equipment.
12. If volt/amp tester is not equipped with an engine tachometer, connect a separate tachometer to the engine.

Test 1
1. Perform the previous test Preparation.
2. Fully engage the parking brake.
3. Start engine.
4. Bring engine speed to 2500 rpm.
5. With engine speed held at 2500 rpm, slowly adjust the rheostat control (load) on the tester to obtain the highest amperage reading. Do not allow voltage to drop below 12 volts. Record the reading. This load test must be performed within 15 seconds to prevent damage to test equipment. On certain brands of test equipment, this load will be applied automatically. Refer to the operating manual supplied with test equipment.
6. The ammeter reading must meet the Minimum Test Amps specifications as displayed in the Generator Ratings chart. This can be found in the Specifications. A label stating a part reference number is attached to the generator case. On some engines this label may be located on the bottom of the case. Compare this reference number to the Generator Ratings chart.
7. Rotate the load control to the OFF position.
8. Continue holding engine speed at 2500. If EVR circuitry is OK, amperage should drop below 15-20 amps. With all electrical accessories and vehicle lighting off, this could take several minutes of engine operation. If amperage did not drop, refer to the appropriate Powertrain Diagnostic Procedures for testing.
9. Remove volt/amp tester.

If minimum amperage could not be met, proceed to Test 2. This test will determine if the generator is faulty, or if EVR circuitry is defective.

Test 2
1. Perform the previous test preparation.
2. Fully engage the parking brake.
3. Connect one end of a jumper wire to a good ground. Connect the other end of jumper wire to the generator field driver (-) terminal. The 2 field terminals (+ and -) are located on the back of the generator. Another way to identify the (-) terminal is to start the engine and measure voltage at both field terminals. The (+) terminal will show battery voltage (12.5-14.5 volts). The (-) terminal will show 3-5 volts less than battery voltage.

CAUTION: Do not connect the jumper ground wire to the generator field source (+) field terminal. Damage to electrical System components may result.

Connecting the jumper wire will remove the voltage regulator circuitry from the test. It will also generate a Diagnostic Trouble Code (DTC).
4. Start engine. Immediately after starting, reduce engine speed to idle. This will prevent any electrical accessory damage from high voltage.
5. Adjust carbon pile rheostat (load) and engine speed in slow increments until a speed of 1250 rpm, and a voltmeter reading of 15 volts is obtained. Immediately record ammeter reading. Do not apply load to system longer than 15 seconds as damage to test equipment may result.

CAUTION: When adjusting rheostat load, do not allow voltage to rise above 16 volts. Damage to the battery and electrical system components may result.

6. The ammeter reading must meet the Minimum Test Amps specifications as displayed in the Generator Ratings chart. This can be found in the Specifications. A label stating a part reference number is attached to the generator case. On some engines this label may be located on the bottom of the case. Compare this reference number to the Generator Rating chart.
7. Remove volt/amp tester.
8. Remove jumper wire.
9. Use the DRB scan tool to erase the DTC. Refer to the DRB screen for procedures.

Results
- If amp reading meets specifications in Test 2, generator is OK.
- If amp reading is less than specified in Test 2, and wire resistance (voltage drop) tests were OK, the generator should be replaced. Refer to Replacement for procedures.
- If Test 2 results were OK, but Test 1 results were not, the problem is in EVR circuitry. Refer to appropriate Powertrain Diagnostic Procedures for diagnosis.