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Introduction
Often when problems with the charging system are being investigated, the alternator is not the problem. A failed battery may cause high charging current and low system voltage, giving a false indication of an alternator failure. If a low battery condition is present, test the condition of the batteries first. Refer to Special Instruction, SEHS7633, "Battery Test Procedure" for more information. Deeply discharged batteries may also cause high charging current and low system voltage, giving a false indication of an alternator failure. If batteries were deeply discharged and a jump-start was performed, use an external battery charging device or operate the machine with an elevated engine speed for a longer period of time to charge the batteries. If the engine cranks slowly, this could be either a problem with the battery or starting system. Refer to Service Magazine, SEPD0020, "Testing The Starter On The Engine" for more information. If a warning indicator for the charging system is ON, refer to Service Magazine, SEBD1751, "Difference Between Alternator Indicator In Electronic Monitoring System (EMS) And Low Voltage Indicator In Operating Monitoring System (OMS)".
ECM diagnostic codes and events should not be used exclusively to determine if the alternator has failed. Further troubleshooting is required to identify the actual failure in the system. When a problem with the charging system is suspected, complete the testing that is outlined in the Special Instruction.
Refer to "Initial Troubleshooting Procedure"to begin troubleshooting. The procedures in this Special Instruction are designed to guide you to the problem with as little testing as possible. Usually, only a few steps will be needed to identify the source of the problem. The tests are labeled as T1-T8, with a descriptive title for each test, as an easy reference.
Important Safety Information
Work safely. Most accidents that involve product operation, maintenance, and repair are caused by failure to observe basic safety rules or precautions. An accident can often be avoided by recognizing potentially hazardous situations before an accident occurs.
A person must be alert to potential hazards. This person should also have the necessary training, skills, and tools to perform these functions properly.
Safety precautions and warnings are provided in this instruction and on the product. If these hazard warnings are not heeded, bodily injury or death could occur to you or to other persons. Caterpillar cannot anticipate every possible circumstance that might involve a potential hazard.
Therefore, the warnings in this publication and the warnings that are on the product are not all inclusive. If a tool, a procedure, a work method, or operating technique that is not recommended by Caterpillar is used, ensure that it is safe for you and for other people to use.
Ensure that the product will not be damaged or the product will be made unsafe by the operation, lubrication, maintenance, or the repair procedures that are used.
Initial Troubleshooting Procedure
- To inspect electrical connections, perform the following:
- Inspect cable terminals for contamination (corrosion, debris, paint. etc.). All cable terminals should be clean and free of any contamination, correct any deficiencies that are found.
- Inspect connection points (junction block terminal, ground boss, etc.) for contamination (corrosion, debris, paint. etc.). All connection points should be clean and free of any contamination, correct any deficiencies that are found.
- Check that proper hardware (washers, nuts, bolts, etc.) is used and installed properly. Only use replacement hardware that contains electrically conductive coatings.
- Ensure that connections are tight and properly torqued.
Note: Some connection points may use copper terminals, ensure that connections are not over-tightened or damage may occur.
- If the connection point uses a protective boot or cover, ensure that the protection device is not damaged. Repair or replace any damaged parts. Ensure that the protective device is properly installed.
- CHECK THE SYSTEM VOLTAGE (with the engine off)
- Measure battery voltage: Connect a voltmeter between the "Batt +" terminal and the "Batt –" terminal. For batteries connected in series to achieve 24 volts, measure voltage across the set of batteries, not an individual battery.
- After measuring battery voltage, measure alternator voltage (battery voltage at the alternator): connect a voltmeter between the alternator “B+” terminal and the alternator “Ground” or “GND” terminal. If the alternator does not have a Ground or GND terminal, connect the voltmeter test lead to bare metal on the case of the alternator. Compare the two voltage readings: Expected result: Alternator voltage is within 1V for 24V systems (0.5V for 12 V system) Results: -- YES - Alternator voltage is within 1V for 24V systems (0.5V for 12 V system). Go to Step 2, Initial Check of Alternator Operation. -- NO – The voltage difference between batteries and alternator is more than 1V for 24V systems (0.5V for 12 V system and Alternator voltage is above 0V. This indicates a high voltage drop in electrical system. - Check Battery cable connections. - Check Battery+ cables and connections between alternator and batteries.-Check Battery-/Ground cables and connections between the alternator and batteries. -- NO – Alternator voltage is 0V. - Check that battery isolation switch is ON. - Check alternator output circuit breaker or fuse. - Check Battery cable connections. - Check Battery+ cables and connections between alternator and batteries. - Check that alternator ground cable is present and inspect connections. - Check Ground cable or strap between engine and machine chassis.
- Before starting the machine, connect a voltmeter between the "B+" terminal and the case of the alternator. Turn OFF all electrical loads.
- Turn the key to the ON position but do not start the engine.
Expected Result: This voltage should be system voltage.
Results:
- YES - The voltage is system voltage. Go to Step 3
- NO - The voltage is less than system voltage. Verify that the batteries are good and verify that battery connections are good. Go to "T4 Alternator Drive System - Check" if the batteries are good.
- INITIAL CHECK OF ALTERNATOR OPERATION.
- INITIAL CHECK OF ALTERNATOR OPERATION a. Connect a voltmeter between the alternator “B+” terminal and the alternator “Ground” or “GND” terminal. If the alternator does not have a Ground or GND terminal, connect the voltmeter lead to bare metal on the case of the alternator. b. Start the engine, set the throttle to at least 75%.
- Start the machine. Set the throttle to at least 75 percent. Read the voltage on the voltmeter.
Expected result: Alternator voltage is higher than the voltage recorded in Step 1. Results: - YES - Alternator voltage is higher than the voltage recorded in Step 1. Alternator voltage is also lower than the maximum voltage specification for the alternator. The alternator is charging, but may not be operating at rated capacity. Proceed to “T1 Alternator Output – Test” - YES - Alternator voltage is higher than the voltage recorded in Step 1. Alternator voltage is also higher than the maximum voltage specification for the alternator. The alternator is over-charging. Proceed to “T8a Alternator Overcharging – Test” - NO – Alternator voltage is not higher than the voltage recorded in Step 1. Proceed to “T4 Alternator Drive System – Check”
Expected Result: The voltage is higher than the voltage that is recorded in the Step 2.
Results:
- YES - The voltage is higher than the voltage observed in the previous Step 2. The voltage is also lower than the maximum voltage that is listed in the specifications for the alternator. The alternator is charging. Although, the alternator may be partially charging. Refer to the following diagnostic flow chart for reference in continued testing. Proceed to "T1 Alternator Output - Test".
- YES - The voltage is higher than the voltage observed in the previous Step 2. The voltage is also higher than the maximum voltage that is listed in the specifications for the alternator. The alternator is over charging. Proceed to "T8a - Alternator Overcharging - Test".
- NO - The voltage is not higher than the voltage that is observed in Step 2. Proceed to "T4 Alternator Drive System - Check".
Note: Severely discharged batteries can cause low system voltage. Severely discharged batteries can occur even while the engine is running above idle, and the alternator is working properly. Proper low engine idle is also important. Most of the alternators in Caterpillar applications are self-excited. These alternators must exceed a turn-on speed before charging will begin. Alternator output can be low at idle.
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| Illustration 1 | g06373072 |
T1 Alternator Output - Test
- Ensure that the batteries are NOT fully charged.
- Fully charged batteries have open circuit voltage above 12.5 V on 12 V systems or 25 V on 24 V systems.
- If the batteries are fully charged, then crank the engine for 30 seconds to discharge the battery. Do not crank the engine for more than 30 seconds and allow a minimum of 120 seconds of cool down before any additional crank attempts. The allowable number of 30 second crank attempts is 3. As an alternative to engine cranking, with the engine OFF, turn ON the lights, or various other electrical loads for 10 minutes. For machines with multiple sets of batteries or high capacity batteries, the lights may need to be operated for more than 10 minutes.
- Use an appropriate current measuring device with "peak and hold" capability and rated at or above the alternator output current rating.
Examples of measuring devices include:
- 9U-5795 AC/DC Current Probe with a DMM (digital multimeter)
- 225-8266 Ammeter Tool Gp
- Equivalent current measuring device
Before clamping the probe around the cable/wire, ensure that the probe is "zeroed". Clamp the probe around the alternator output cable. Read the current value in amps.
- Set the digital multimeter to "peak hold" or "max mode" on the "mV" scale.
- Turn on all electrical accessories: lights, air conditioning, and radio.
- Start the machine, and immediately set the throttle to at least 75 percent. The peak current will appear on the voltmeter in "peak hold" or "max" mode. Read the current value in amps.
Expected Result: This current reading should be at least 90 percent of the specified peak output.
Results:
- OK - The current is at least 90 percent of the specified peak output. Go to "T2a - Undesired Electrical System Current - Test (For Machines Equipped With A Main Disconnect Switch)" OR "T2b - Undesired Electrical System Current - Test (For Any Machine)".
- NOT OK - The current is less than 90 percent of the specified peak output. Go to "T4 Alternator Drive System - Check".
T2a - Undesired Electrical System Current - Test (For Machines Equipped With A Main Disconnect Switch)
- Turn off all the accessories. Turn the keyswitch to the OFF position.
- Use an appropriate current measuring device with "peak and hold" capability and rated at or above the alternator output current rating.
Examples of measuring devices include:
- 9U-5795 AC/DC Current Probe with a DMM (digital multimeter)
- 225-8266 Ammeter Tool Gp
- Equivalent current measuring device
Before clamping the probe around the cable/wire, ensure that the probe is "zeroed". Clamp the probe around the alternator output cable. Read the current value in amps.
Expected Result: The current is below 2 A.
Results:
- YES - The current is below 2 A. Continue to Step 3.
- NO - The current is above 2 A. There is a current draw in the system. Go to "T5 Alternator Current - Test".
- Turn the disconnect switch to the ON position. Connect a multimeter across the disconnect switch terminals. Connect the red lead to the terminal on the frame side. Connect the black lead to the terminal on the battery side. Use the 10A connections to avoid damage.
- Turn off the disconnect switch and read the current.
Expected Result:The current is below .050 A (50 mA).
Note: The standard acceptable current draw is 50 mA. A current draw above 50 mA usually indicates a problem. However, some large machines with multiple electronic control modules have a higher acceptable limit. Contact a Caterpillar dealer for more information.
Results:
- YES - The current is below 0.050 A. The charging system is good. The fault is possibly an intermittent draw in the system. The batteries may be faulty. Check that NO accessories were ON during the test.
- NO - The current is above 0.050 A. There is a draw in the system. Go to "T5 Alternator Current - Test".
T2b - Undesired Electrical System Current - Test (For Any Machine)
- Turn off all accessories. Turn the keyswitch to the OFF position.
- Use an appropriate current measuring device with "peak and hold" capability and rated at or above the alternator output current rating.
Examples of measuring devices include:
- 9U-5795 AC/DC Current Probe with a DMM (digital multimeter)
- 225-8266 Ammeter Tool Gp
- Equivalent current measuring device
Before clamping the probe around the cable/wire, ensure that the probe is "zeroed". Clamp the probe around the alternator output cable. Read the current value in amps.
Expected Result: The current is below 2 A.
Results:
- YES - The current is below 2 A. Continue to Step 3.
- NO - The current is above 2 A. There is a current draw in the system. Go to "T5 Alternator Current - Test".
- Remove the ground cable from the battery terminal. For systems with 4 batteries, or 12 V systems with 2 batteries, disconnect the ground cables from both negative batteries.
- Connect a multimeter between the disconnected battery ground cable and one of the negative battery terminals. Connect the red positive lead of the multimeter to the cable. The negative lead should be connected to the battery terminal. Use the 10A connections to avoid damage.
Expected Result:The current is below .050 amperes (50 mA).
Note: The standard acceptable current draw is 50 mA. A current draw above 50 mA usually indicates a problem. However, some large machines with multiple electronic control modules have a higher acceptable limit. Contact a Caterpillar dealer for more information.
Results:
- YES - The current is below 0.050 A. The charging system is good. The fault is possibly an intermittent draw in the system. The batteries may be faulty. Check that NO accessories were ON during the test.
- NO - The current is above 0.050 A. There is a draw in the system. Go to "T5 Alternator Current - Test".
T3 Charging System - Test
- Verify that the alternator B+ terminal nut is tight and verify that the wire has a good connection to the B+ terminal.
- Start the engine and set the throttle to at least 75 percent. Turn ON all electrical accessories for all test steps below. Allow the engine to run for at least 3 minutes before continuing to Step 3. The following table will help in making calculations during this test.
Show/hide table
Table 1 Test Step Voltage Reading Voltage should be below this value for a 12 V system. Voltage should be below this value for a 24 V system. 4 5 4 minus 5 = 1.0 V 2.0 V 6 7 6 minus 7 = 0.5 V 1.0 V 8 0.5 V 1.0 V - Measure alternator voltage.
- Connect a voltmeter between the alternator "B+" terminal and the alternator ground or "GND" terminal. If the alternator does not have a ground or "GND" terminal, connect the voltmeter test lead to bare metal on the case of the alternator.
- Measure the voltage across the battery. Put the red lead on the positive battery terminal, and put the black lead on the negative battery terminal. Step 4 should be completed as quickly as possible after Step 3.
Expected Result: On 12 V systems, the voltage is less than or equal to the voltage that is recorded in Step 3. However, the voltage is within 1 V. On 24 V systems, the voltage is within 2 V.
Results:
- YES - If the voltage in Step 3 is not more than 1 V for 12 V systems (2 V for 24 V systems) higher than the voltage in Step 4, this test is complete and the related wiring is correct now. Replace the alternator or disassemble the alternator and repair.
- NO - If the voltage in Step 3 is more than 1 V for 12 V systems (2 V for 24 V systems) higher than the voltage in Step 4, there is high circuit resistance: corrosion, loose connections, and damaged wiring. Continue to Step 5.
- Check the voltage between the machine frame and the alternator B+ terminal. Record the voltage.
- Check the voltage between the machine frame and the positive battery post. Step 6 should be completed as quickly as possible after Step 5.
Expected Result: The voltage difference between Step 5 and Step 6 does not exceed 1 V on 24 V systems or 0.5 V on 12 V systems.
Results:
- YES - The voltage difference does not exceed the tolerance. The charging circuit is good. Go to Step 7.
- NO - The voltage difference exceeds the tolerance. There is high resistance in the charging circuit: loose cables, corroded cables, damaged cables, and faulty circuit breaker. Correct the problem and retest the system.
- Check the voltage between the negative battery post and the alternator case ground.
Expected Result: The voltage does not exceed 1 V on 24 V systems or 0.5 V on 12 V systems.
Results:
- YES - The voltage difference does not exceed the tolerance. The ground circuit is good. There is an internal problem with the alternator. Go to "T6 Residual Magnetism Restoration".
- NO - The voltage difference exceeds the tolerance. There is high resistance in the ground circuit: loose cables, corroded cables, loose alternator mounting, and poor engine ground. Correct the problem and retest the system.
T4 Alternator Drive System - Check
- Check the condition of the alternator drive belt. If the drive belt is oily, clean the pulleys. Replace the drive belt, and retest the system. If the drive belt is wet, dry the belt and retest the system. If the drive belt is worn, replace the belt and retest the system.
- Check the tension of the alternator drive belt. If the tension is off, adjust the tension.
- Check the pulley retention nut on the alternator shaft. If the nut is found to be loose, inspect all parts for any signs of damage and replace as necessary. Clean the mating surfaces of all parts, reassemble the parts and tighten the nut to the appropriate torque value for the specific alternator.
Use of a tool to hold the shaft while tightening the pulley retention nut may be necessary, use the appropriate tool for the specific alternator. Retest the system.
- If all the previous steps find no problems, go to "T3 Charging System - Test".
T5 Alternator Current - Test
- Turn the keyswitch to the OFF position.
- Use an appropriate current measuring device with "peak and hold" capability and rated at or above the alternator output current rating.
Examples of measuring devices include:
- 9U-5795 AC/DC Current Probe with a DMM (digital multimeter)
- 225-8266 Ammeter Tool Gp
- Equivalent current measuring device
- Before clamping the probe around the cable/wire, ensure that the probe is "zeroed". Clamp the probe around the alternator output cable. Read the current value in amps.
- Disconnect the B+ terminal wire from the alternator. Connect the red lead of the multimeter to the wire that was disconnected. Connect the black lead of the multimeter to the alternator B+ terminal. Set the multimeter on the 10 amp scale. Read the current.
Expected Result: The current is under 0.015 A.
Results:
- YES - The current is under 0.015 A. The alternator is operating correctly. There is a current draw on the machine. Go to "T7 Identifying Source Of Current Draw - Test".
- NO - The current is over 0.015 A. There is an internal problem with the alternator. Go to "T6 Residual Magnetism Restoration".
T6 Residual Magnetism Restoration
This test is only for self-excited alternators. Refer to Service Magazine, SEBD1672, July 1986, "Brushless Alternators May Not Charge In Certain Conditions" for additional information.
- Start the engine and set the throttle to at least 75 percent.
- Connect a voltmeter between the "B+" terminal and the alternator case ground.
- If a wire is connected, disconnect the wire from the "R" terminal.
Expected Result: The voltage does not change.
Results:
- YES - The voltage stays the same. Continue to Step 4.
- NO - The voltage rises and the alternator begins charging. The wire to the "R" terminal is shorted. Repair the wiring or replace the wiring. Go to "Initial Troubleshooting Procedure" and retest the system.
- Connect one end of a jumper wire to the "B+" terminal of the alternator.
- Connect the other end of the jumper wire to the "R" terminal ("D+" terminal for Bosch) of the alternator for 2 seconds.
Expected Result: The voltage output rises on the "B+" terminal.
Results:
- OK - The voltage output rises. The alternator is now charging. Go to "Initial Troubleshooting Procedure" and retest the system.
- NOT OK - The voltage output does not rise. If the alternator has a wire that is connected to the "I" terminal, then go to Step 6. Otherwise, disassemble the alternator and repair the alternator. Otherwise, replace the alternator.
- Remove the wire that is connected to the "I" terminal. Check for a rise in voltage on the "B+" terminal.
Expected Result: The voltage rises.
Results:
- YES - The voltage rises. There is a short in the wiring to the terminal. Repair the wiring or replace the wiring. Go to "Initial Troubleshooting Procedure" and retest the system.
- NOT OK - The voltage output does not rise. Disassemble the alternator and repair the alternator. Otherwise, replace the alternator.
T7 Identifying Source Of Current Draw - Test
- Make sure that every electrical component is turned OFF. Make sure that the keyswitch is turned OFF. Make sure that the dome lights are OFF.
- Use an appropriate current measuring device that is rated at or above the rating of the largest circuit to be measured.
- 9U-5795 AC/DC Current Probe with a DMM (digital multimeter)
- 225-8266 Ammeter Tool Gp
- Equivalent current measuring device
- Before clamping the probe around the cable/wire, ensure that the probe is "zeroed". Clamp the probe around the main ground cable with the positive side of the current probe away from the battery.
Note: If this step is not taken the ammeter will not read the current accurately.
- Monitor the current and remove fuses and breakers one at a time. Check the current after each fuse (breaker) is removed. After removing a fuse (breaker) and observing the current, reinstall the fuse (breaker). Start with the main fuses (circuit breakers) first, and proceed to smaller circuits.
- If a removal of a fuse causes the current to drop, then the problem is in that circuit.
- Check if any components on the circuit are ON.
- If everything is OFF, disconnect electrical components on that circuit one at a time and monitor current.
- After all the components in that circuit have been disconnected, check the current. If the problem still exists, then check the wiring for corrosion or shorts to ground.
- If the source of current draw is not found after removing all fuses and circuit breakers, look for any other electrical loads that do not pass through the fuse panel(s). This may include any electrical devices added to the machine that are connected either directly to the batteries, or to any battery positive junction block, or other connection point.
Note: The standard acceptable current draw is 50 mA. A current draw above 50 mA usually indicates a problem. However, some large machines with multiple electronic control modules have a higher acceptable limit. Contact a Caterpillar dealer for more information.
T8a - Alternator Overcharging - Test
This test is for alternators with the following terminals:
- "IG"
- "S"
- other sense terminal
- Clean the connection and tighten the connection to the wiring terminal on the alternator.
- Verify that the alternator B+ terminal nut is tight and verify that the wire has a good connection to the "B+" terminal.
- Start the engine and set the throttle to at least 75 percent. Turn ON all electrical accessories for all test steps below. Allow the engine to run for at least 3 minutes before continuing to Step 4. The following table will help in making calculations during this test.
Show/hide table
Table 2 Test Step Voltage Reading The voltage should be below this value for a 12 V system. The voltage should be below this value for a 24 V system. 5 6 5 minus 6 = 1.0 V 2.0 V 7 8 7 minus 8 = 0.5 V 1.0 V - Measure the voltage between the alternator "B+" terminal and the alternator case ground.
- Measure the voltage across the battery. Put the red lead on the positive battery terminal, and put the black lead on the negative battery terminal. Step 5 should be completed as quickly as possible after Step 4.
Expected Result: On 12 V systems, the voltage is within 1 V of the voltage that is recorded in Step 4. On 24 V systems, the voltage is within 2 V.
Results:
- YES - If the voltage in Step 4 is not more than 1 V for 12 V systems (2 V for 24 V systems) higher than the voltage in Step 5, this step is complete and the related wiring is correct now. Go to Step 8.
- NO - If the voltage in Step 4 is more than 1 V for 12 V systems (2 V for 24 V systems) higher than the voltage in Step 5, there is high circuit resistance: corrosion, loose connections, and damaged wiring. Go to Step 6.
- Check the voltage between the machine frame and the alternator B+ terminal. Record the voltage.
- Check the voltage between the machine frame and the positive battery post. Step 7 should be completed as quickly as possible after Step 6.
Expected Result: The voltage difference between Step 6 and Step 7 does not exceed 1 V on 24 V systems or 0.5 V on 12 V systems.
Results:
- YES - The voltage difference does not exceed the tolerance. The charging circuit is good. Go to Step 8.
- NO - The voltage difference exceeds the tolerance. There is high resistance in the charging circuit: loose cables, corroded cables, damaged cables, faulty circuit breaker, and faulty main relay. Correct the problem. Go to "Initial Troubleshooting Procedure" and retest the system.
- Start the engine and set the throttle to at least 75 percent. Turn OFF all the accessories.
Show/hide table
Illustration 2 g00496660 Special Wire Probe Technique For Denso Alternators Note: Denso G3B, K3A, and L3A Alternators Only: Insert a 7X-1710 Multimeter Probe Group into the rear of the middle wire in the connector. Refer to figure 2. Insert the probe (spoon lead) between the black seal that surrounds the wire and the outer shell of the connector. Do not insert the probe between the wire insulation and the black seal. This terminal ("IG") is the terminal for excitation.
- Measure the voltage between the sense terminal and the case of the alternator.
Expected Result: The voltage at the sense terminal is above the specification.
Results:
- YES - The voltage is over specification. There is an internal malfunction in the alternator. Refer to the appropriate service manual for the alternator to test the internal components and connections.
- NO - The voltage is below that found in the initial tests (B+ to alternator case). The sense circuit in the machine has high resistance. Correct the problem and retest the system . Go to "Initial Troubleshooting Procedure".
T8b - Alternator Overcharging - Test (Continued)
This test is for alternators without an "IG", "S", or other sense terminal.
- Clean and tighten the connection to the wiring terminal on the alternator.
- Verify that the alternator B+ terminal nut is tight and verify that the wire has a good connection to the B+ terminal.
- Run the engine at 75 percent. Turn ON all electrical accessories for all test steps below. Allow the engine to run for at least 3 minutes before continuing to Step 4. The following table shows how the measurements taken during this test will be used.
Show/hide table
Table 3 Test Step Voltage Reading Voltage should be below this for 12 V system Voltage should be below this for 24 V system 5 6 5 minus 6 = 1.0 V 2.0 V 7 8 7 minus 8 = 0.5 V 1.0 V - Measure the voltage between the alternator B+ terminal and the alternator case ground.
- Measure the voltage across the battery. Put the red lead on the positive battery terminal, and put the black lead on the negative battery terminal. Step 5 should be completed as quickly as possible after Step 4.
Expected Result: On 12 V systems, the voltage is within 1 V of the voltage recorded in Step 4. On 24 V systems, the voltage is within 2 V.
Results:
- YES - If the voltage in Step 4 is not more than 1 V for 12 V systems (2 V for 24 V systems) higher than the voltage in Step 5, this step is complete and the related wiring is correct now. There is an internal malfunction in the alternator. Refer to the appropriate service manual for the alternator to test the internal components and connections.
- NO - If the voltage in Step 4 is more than 1 V for 12 V systems (2 V for 24 V systems) higher than the voltage in Step 5, there is high circuit resistance: corrosion, loose connections, and damaged wiring. Go to Step 6.
- Check the voltage between the machine frame and the alternator B+ terminal. Record the voltage.
- Check the voltage between the machine frame and the positive battery post. Step 7 should be completed as quickly as possible after Step 6.
Expected Result: The voltage difference between Step 6 and Step 7 does not exceed 1 V on 24 V systems or 0.5 V on 12 V systems.
Results:
- YES - The voltage difference does not exceed the tolerance. The charging circuit is good. There is an internal malfunction in the alternator. Refer to the appropriate service manual for the alternator to test the internal components and connections.
- NO - The voltage difference exceeds the tolerance. There is high resistance in the charging circuit: loose cables, corroded cables, damaged cables, faulty circuit breaker, and faulty main relay. Correct the problem. Go to "Initial Troubleshooting Procedure" and retest the system.