Initial Inspection and Diagnostic Overview

The following procedures may be used to diagnose the charging system if:
- the generator lamp (if equipped) is illuminated with the engine running
- the voltmeter (if equipped) does not register properly an undercharged or overcharged battery condition occurs. Remember that an undercharged battery is often caused by:
- accessories being left on with the engine not running
- a faulty or improperly adjusted switch that allows a lamp to stay on. See Ignition-Off Draw Test in Starting and Charging/Battery for more information.

Inspection
To perform a complete test of the charging system, refer to the appropriate Powertrain Diagnostic Procedures and the DRB scan tool. Perform the following inspections before attaching the scan tool.
1. Inspect the battery condition. Refer to Starting and Charging/Battery for procedures.
2. Inspect condition of battery cable terminals, battery posts, connections at engine block, starter solenoid and relay They should be clean and tight. Repair as required.
3. Inspect all fuses in both the fuse block and Power Distribution Center (PDC) for tightness in receptacles. They should be properly installed and tight. Repair or replace as required.
4. Inspect generator mounting bolts for tightness. Replace or tighten bolts if required. Refer to the Starting and Charging/Charging System/Alternator/Generator Removal/Installation for torque specifications.
5. Inspect generator drive belt condition and tension. Tighten or replace belt as required.
6. Inspect automatic belt tensioner (if equipped).
7. Inspect connections at generator field, battery output, and ground terminals. Also check ground connection at engine. They should all be clean and tight. Repair as required.

Current Output Test
The current output test will determine if the charging system can deliver its minimum test current (amperage) output.

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 Powertrain Management/Computer and Control System for 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 Powertrain Management/Computer and Control System for the appropriate Powertrain Diagnostic Procedures.
2. Before starting test, make sure battery is in good condition and is fully-charged. See Starting and Charging/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 Starting and Charging/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 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 at the end. 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 Powertrain Management/Computer and Control System for 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.

Generator Terminals (Typical Wiring Harness Shown):

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. To locate and identify the (-) terminal and circuit. 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 at the end of this . 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/lamp 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 Service and Repair for procedures.
- If Test 2 results were OK, but Test 1 results were not, the problem is in EVR circuitry. Refer to Powertrain Management/Computer and Control System for appropriate Powertrain Diagnostic Procedures for diagnosis.

Charging System Resistance Test

Generator Terminals (Typical Wiring Harness Shown):

These tests will show the amount of voltage drop across the generator output wire, from the generator output (B+) terminal to the battery positive post. They will also show the amount of voltage drop from the ground (-) terminal on the generator to the battery negative post. A typical generator wiring harness is shown. Wiring harness routing as shown in may he slightly different depending on vehicle model and/or engine.

A voltmeter with a 0-18 Volt DC scale should be used for these tests. By repositioning the voltmeter test leads, the point of high resistance (voltage drop) can easily be found.


Preparation
1. Before starting test, make sure battery is in good condition and is fully-charged. See Starting and Charging/Battery for more information.
2. Check condition of battery cables at battery. Clean if necessary.
3. Start the engine and allow it to reach normal operating temperature.
4. Shut engine off.
5. Connect an engine tachometer.
6. Fully engage the parking brake.

Test
1. Start engine.
2. Place heater blower in high position.
3. Turn on headlamps and place in high-beam position.
4. Turn vehicle interior lamps on.
5. Bring engine speed up to 2400 rpm and hold.
6. Testing (+) circuitry:
a. Touch the negative lead of voltmeter directly to battery positive post.
b. Touch the positive lead of voltmeter to the B+ output terminal stud on the generator (not the terminal mounting nut). Voltage should be no higher than 0.6 Volts. If voltage is higher than 0.6 Volts, touch test lead to terminal mounting stud nut and then to the wiring connector. If voltage is now below 0.6 Volts, look for dirty, loose or poor connection at this point. Also check condition of the generator output wire-to-battery bullet connector (if equipped). Refer to Wiring for connector location. A voltage drop test may be performed at each (+) connection in this circuit to locate the excessive resistance.
7. Testing (-) circuitry:
a. Touch the negative lead of voltmeter directly to battery negative post.
b. Touch the positive lead of voltmeter to the ground terminal stud on the generator case (not the terminal mounting nut). Voltage should be no higher than 0.3 Volts. If voltage is higher than 0.3 Volts, touch test lead to terminal mounting stud nut and then to the wiring connector. If voltage is now below 0.3 Volts, look for dirty, loose or poor connection at this point. A voltage drop test may be performed at each (-) connection in this circuit to locate the excessive resistance. This test can also be performed between the generator case and the engine. If test voltage is higher than 0.3 Volts, check for corrosion at generator mounting points or loose generator mounting.

On-Board Diagnostic Test For Charging System
The Powertrain Control Module (PCM) monitors critical input and output circuits of the charging system, making sure they are operational. A Diagnostic Trouble Code (DTC) is assigned to each input and output circuit monitored by the On-Board Diagnostic (OBD) system. Some circuits are checked continuously and some are checked only under certain conditions.

For DTC information, refer to Diagnostic Trouble Codes in Powertrain Management/Computers and Control Systems. This will include a complete list of DTC's including DTC's for the charging system.