26SI Series Alternator – Starting Motor Does Not Turn or Turns Slowly

System Operation Description:

The possible causes of this failure are listed below:

  • The battery is discharged or the battery has failed.

  • The cables to the starter have failed.

  • The ignition switch has failed.

  • The engine is locked.

  • The starting motor solenoid has failed.

  • The starting motor has an internal problem.

The following tables will be referenced in troubleshooting the starting motor.

Table 1
TYPICAL SYSTEM VOLTAGE DURING CRANKING AT VARIOUS AMBIENT TEMPERATURES    
Temperature     12 Volt System     24 Volt System    
-23 °C (-9.4 °F) to
-7 °C (19.4 °F)    
6 to 8 Volts     12 to 16 Volts    
-7 °C (19.4 °F) to
10 °C (50 °F)    
7 to 9 Volts     14 to 18 Volts    
10 °C (50 °F) to
27 °C (80 °F)    
8 to 10 Volts     16 to 20 Volts    
Table 2
MAXIMUM ACCEPTABLE VOLTAGE DROPS DURING CRANKING    
Circuit     12 Volt System     24 Volt System    
Battery negative post to the negative terminal on the starting motor     0.7 Volts     1.4 Volts    
Drop across disconnect switch     0.5 Volts     1.0 Volts    
Battery positive post to the positive terminal on the solenoid     0.5 Volts     1.0 Volts    
Battery terminal of the solenoid to the motor terminal of the solenoid     0.4 Volts     0.8 Volts    

Test Step 1. CHECK THE BATTERY VOLTAGE

  1. Attempt to crank the engine. Measure the battery voltage with the digital multimeter. Measure the voltage at the battery posts. Do not measure the voltage at the terminal of the battery cable.
  1. Compare the voltage to table 1.

Expected Result:

The battery voltage is equal to or greater than the voltage in table 1.

Results:

  • OK – Battery voltage is correct. Go to test step 2.

  • NOT OK – Battery voltage is too low.

    Repair: Check the charging system. See Special Instruction, REHS0354, “Charging System Troubleshooting”.

    STOP

Test Step 2. TEST THE DISCONNECT SWITCH

  1. Ensure that the disconnect switch is in the CLOSED position.
  1. Measure the resistance across the terminals of the disconnect switch.

Expected Result:

The resistance should be less than 5 ohms.

Results:

  • OK – The resistance is less than 5 ohms. The disconnect switch operates properly. Proceed to test step 3.

  • NOT OK – The resistance is greater than 5 ohms. The disconnect switch has failed.

    Repair: Replace the battery disconnect switch.

    STOP

Test Step 3. TEST CABLES FROM THE BATTERY TO THE STARTING MOTOR

  1. Visually inspect the battery cable terminals for the following conditions:

    • Loose connections

    • Corroded cables

Expected Result:

The cables should be clean and the cables should be tight.

Results:

  • OK – Battery cables are in good condition. Proceed to test step 4.

  • NOT OK – Battery cables are faulty.

    Repair: Clean the terminals or replace the terminals. Tighten the terminals.

    STOP

Test Step 4. TEST CABLES FROM THE BATTERY TO THE STARTING MOTOR FOR VOLTAGE DROP

  1. Attempt to crank the engine. Measure the voltage from “Mtr” terminal to ground.

Expected Result:

The battery voltage is less than the voltage in table 2.

Results:

  • OK – The voltage drop is less than the specified voltage drop. Proceed to test step 5.

  • NOT OK – The voltage drop is greater than the specified voltage drop.

    Repair: Repair the cables or replace the cables. Repeat the voltage measurement. If the voltage remains low, measure the voltage drop across each component that is listed in table 2. Replace all components that are out of specification.

    STOP

Test Step 5. CHECK ENGINE ROTATION

  1. Remove the starter from the engine.
  1. Turn the engine by hand.

Expected Result:

The engine turns with normal effort.

Results:

  • YES – The engine turns with normal effort. Proceed to test step 6.

  • NO – The engine turns with more than normal effort. The engine needs to be serviced.

    Repair: Repair the engine. Refer to the Disassembly and Assembly manual for the engine.

    STOP

Test Step 6. TEST THE START RELAY

  1. Locate the start relay for the starter.
  1. Remove any power sources from the relay contacts before performing this test.
  1. Attempt to crank the engine. Measure the resistance across the start relay.

Expected Result:

The resistance should be less than 5 ohms.

Results:

  • OK – The resistance is less than 5 ohms. The start relay operates properly. Proceed to test step 7.

  • NOT OK – The resistance is greater than 5 ohms. The start relay has failed.

    Repair: Replace the start relay.

    STOP

Test Step 7. TEST THE STARTING MOTOR SOLENOID

  1. Perform the starting motor solenoid test. See Testing and Adjusting, “Starting Motor Solenoid – Test”.

Expected Result:

The solenoid operates properly.

Results:

  • OK – The solenoid operates properly. Go to test step 8.

  • NOT OK – The solenoid has failed.

    Repair: Replace the solenoid.

    STOP

Test Step 8. TEST THE INTERNAL COMPONENTS OF THE STARTING MOTOR

  1. Check starting motor brushes. See Testing and Adjusting, “Brush and Brush Holder – Check”.

Expected Result:

The brushes of the starting motor function properly.

Results:

  • OK – The brushes of the starting motor function properly.

    Repair: Perform the component tests for the starting motor. See the proper test in the Testing and Adjusting section.

    STOP

  • NOT OK – The brushes have failed.

    Repair: Replace brushes or repair brushes. Repair the brush holder or replace the brush holder.

    STOP

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