3412, 3412C, and 3412E Generator Set Engines Caterpillar

The engine speed switch monitors the engine rpm for overspeed conditions and for crank termination.

Crank termination signals when cranking must be terminated. When the crank termination speed is reached, terminal 10 is energized in order to start the engine hour meter.

Illustration 1	g01644993
Engine speed switch

Test Step 1. Check the Engine Speed Switch for Supply Voltage

1. Make sure that the wiring is connected according to the wiring schematic.

2. Turn the engine control switch to the ON position.

3. Measure the voltage between terminal 6 and terminal 5 of the engine speed switch (ESS).

4. Measure the voltage between ESS terminal 11 and terminal 5.

5. Turn the engine control switch to the OFF position.

Expected Result:

The voltage is between 22 VDC and 27 VDC.

Results:

• OK - The voltage is between 22 VDC and 27 VDC. Proceed to Test Step 2.

• NOT OK - The voltage is not between 22 VDC and 27 VDC.

  Repair: The ESS is not receiving the correct voltage. Repair the harness or replace the harness.

  STOP

Test Step 2. Check the Voltage at Terminal 10 at 0 rpm Input

1. Turn the engine control switch to the ON position.

2. Measure the voltage between ESS terminal 10 and terminal 5.

   Note: The hour meter must be connected during the test of the crank terminate in order to provide a load. The positive terminal of the engine hour meter should be connected to ESS terminal 10.

3. Turn the engine control switch to the OFF position.

Expected Result:

The voltage should be less than 1 VDC.

Results:

• OK - The voltage is less than 1 VDC. Proceed to Test Step 3.

• Not OK - The voltage is greater than 1 VDC.

  Repair: Check the diode between ESS terminal 8 and ESS terminal 10. If the voltage is still high, remove all wires from terminal 10. This should show the voltage source. If the problem is not resolved, replace the ESS.

  STOP

Test Step 3. Check Voltage at Terminal 10 at Crank Terminate rpm Input

1. Disconnect the harness of the engine speed input at ESS Terminal 3 and terminal 4.

2. Connect a signal generator to ESS terminal 3 and terminal 4.

3. Set the signal generator frequency to 0 Hz.

4. Turn the engine control switch to the ON position.

5. Slowly increase the frequency. Monitor the voltage between ESS terminal 5 and terminal 10. Record the frequency that causes the voltage to increase to battery positive voltage.

6. Turn the engine control switch to the OFF position.

Expected Result:

The voltage between ESS terminal 10 and ESS terminal 5 increases to battery positive voltage when the frequency reaches 875 Hz to 920 Hz.

Results:

• OK - The voltage between ESS terminal 10 and ESS terminal 5 increases to battery positive voltage when the frequency reaches 875 Hz to 920 Hz. Proceed to Test Step 4.

• NOT OK - The voltage between ESS terminal 10 and ESS terminal 5 does not increase to battery positive voltage when the frequency reaches 875 Hz to 920 Hz.

  Repair: Refer to Troubleshooting, "Crank Terminate - Calibrate".

  STOP

Test Step 4. Check the Voltage at the Engine Hour Meter

1. Turn the engine control switch to the ON position.

2. Measure the voltage between the terminals of the engine hour meter.

3. Turn the engine control switch to the OFF position.

Expected Result:

The voltage between the terminals of the engine hour meter is +battery.

Results:

• OK - The voltage between the terminals of the engine hour meter is +battery. Replace the hour meter if the hour meter is not recording engine hours of operation. Proceed to Test Step 5.

• NOT OK - The correct voltage is present at the ESS but not at the hour meter. Repair the harness or replace the harness.STOP

Test Step 5. Reduce the Frequency and Check the Voltage at Terminal 10

1. Disconnect the harness of the engine speed input at ESS terminal 3 and terminal 4.

2. Connect a signal generator to ESS terminal 3 and terminal 4.

3. Turn the engine control switch to the ON position.

4. Set the signal generator frequency to 900 Hz.

5. Slowly decrease the frequency. Monitor the voltage between ESS terminal 5 and terminal 10. Record the frequency that causes the voltage to drop below 1.0 VDC.

6. Turn the engine control switch to the OFF position.

Expected Result:

The voltage between terminal 5 and terminal 10 should drop below 1.0 VDC when the frequency is less than 20 Hz. The frequency is equivalent to 9 rpm.

Results:

• OK - The voltage between terminal 5 and terminal 10 drops below 1.0 VDC when the frequency is less than 20 Hz. Proceed to Test Step 6.

• NOT OK - The voltage between terminal 5 and terminal 10 does not drop below 1.0 VDC when the frequency is less than 20 Hz.

  Repair: Replace the ESS.

  STOP

Test Step 6. Check the Operation of the Crank Terminate

1. Turn the engine control switch to the OFF position.

2. Reconnect the harness of the engine speed input.

3. Use a test lamp and monitor the voltage across the engine hour meter. Monitor the test lamp during the starting of the engine.

Expected Result:

The test lamp illuminates as the engine accelerates from cranking rpm to idle rpm.

Results:

• OK - The test lamp illuminates as the engine accelerates from cranking rpm to idle rpm.

  Repair: The ESS is functioning properly.

  STOP

• NOT OK - The test lamp does not illuminate as the engine accelerates from cranking rpm to idle rpm.

  Repair: The crank terminate functions properly with a signal generator, but not with the harness of the engine speed input. Repair the engine speed input circuit.

  STOP