0342923 JOHNSON COVER, Cylinder head

Initial Troubleshooting Procedure
CHECK THE RESISTANCE IN THE EXCITATION CIRCUIT. This step is only for alternators with external excitation when the terminal for excitation is labeled: "1", "REG" and "D+". See "Alternator Specifications" if the method of excitation is unknown. Go to Step 3 if your alternator is self-excited. Proceed to Step 2 if the excitation terminal of the alternator has the label "IG".
Turn the key start switch to the ON position.
Verify voltage at the excitation terminal. Connect the red lead from a multimeter to the excitation terminal. Connect the black lead to a ground source (alternator case ground).
Read the voltage that is shown on the multimeter.Expected Result: The voltage reads at least .2 volts.Results:
YES - The voltage reads .2 volts or more. The excitation circuit is correct. Proceed to Step 3.
NO - The voltage is less than .2 volts. There is a failure in the wiring harness to the alternator or there is a poor electrical connection. Correct the problem and operate the machine. Watch for a recurrence of the problem.
CHECK THE RESISTANCE IN THE EXCITATION CIRCUIT (CONTINUED). This step is only for alternators with external excitation when the terminal for excitation is labeled: "IG". See "Alternator Specifications" if the method of excitation is unknown. Go to Step 3 if your alternator is self-excited.
Turn the key start switch to the ON position.
Verify voltage at the excitation terminal. Connect the red lead from a multimeter to the excitation terminal. Connect the black lead to a ground source. The case of the alternator can be used as a good source of ground. Note: For Denso G3B, K3A, and L3A alternators, Insert a 7X-1710 Multimeter Probe Group into the rear of the middle wire in the connector. See figure 1 below. 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.
Illustration 1 g00496660
Special Technique Using A Wire Probe On The Denso Alternator
Read the voltage that is shown on the multimeter.Expected Result: The voltage is within .5 volts of battery voltage.Results:
YES - The voltage reads battery voltage. The excitation circuit is correct. Proceed to Step 3.
NO - The voltage is more than .5 volts less than battery voltage. There is a failure in the wiring harness to the alternator or there is a poor electrical connection. Correct the problem and operate the machine. Watch for a recurrence of the problem.
CHECK THE SYSTEM VOLTAGE.
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 4
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 THE OPERATION OF THE ALTERNATOR.
The voltmeter remains connected in the configuration from Step 3.
Start the machine. Set the throttle to at least 75 percent. Read the voltage on the voltmeter.Expected Result: The voltage is higher than the voltage that was recorded in the previous Step 3. Results:
YES - The voltage is higher than the voltage observed in the previous Step 3. The voltage is also lower than the maximum voltage that is listed in the specifications for the alternator. The alternator is partially charging. See 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 3. 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 ""T8 Alternator Overcharging - Test"".
NO - The voltage is not higher than the voltage observed in Step 3. 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.
Illustration 2 g00508188
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. This action reduces the battery voltage. Operate the lights for 10 minutes while the engine is off as an alternative.
Connect the 9U-5795 Current Probe to a DMM (digital multimeter) or use a 225-8266 Ammeter Tool Gp . The multimeter must have a peak hold feature. Clamp the probe around alternator output wire "B+". Before clamping the probe around the wire, ensure that the probe is "zeroed" .
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. 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 of the accessories. Turn the keyswitch