C27 Petroleum Generator Set Engines Caterpillar

Use this procedure to troubleshoot the electrical system if problem is suspected with power to the Electronic Control Module (ECM). Also use this procedure if any one of the diagnostic codes in Table are active or easily repeated.

The engine ECM requires the keyswitch to be in the ON position in order to maintain communications with Caterpillar Electronic Technician (ET).

This procedure tests whether proper voltage is being supplied to the Electronic Control Module (ECM).

The ECM is continuously powered with +Battery voltage that is supplied to inputs P1-48, P1-52, P1-53, P1-55, and P1-57 and P1-70 (keyswitch). If an emergency stop condition is initiated, the ECM relay will be energized and battery voltage will be removed from the ECM.

Power to the ECM is provided by a set of normally closed contacts that are in ECM relay. The ECM relay is controlled by a set of normally open contacts in the emergency stop switch. When the emergency stop switch is placed in the STOP position, the contacts in the emergency stop switch are closed and +24 VDC is supplied to the control circuit for the ECM relay. This opens the contacts in the relay and power is removed from the ECM.

Opening the battery disconnect switch will also remove power from the ECM. When the battery disconnect switch is placed in the OFF position, the ground connection to inputs P1-61, P1-63, P1-65, P1-67, and P1-69 of the ECM is removed.

During an engine start sequence, the Starting Motor Magnetic Switch (SMMS) is used by the ECM to engage the starting motor. Voltage for the control solenoid for the SMMS is supplied by the ECM. When the ECM supplies the signal, the SMMS is energized. This powers the starting solenoid and the starter is engaged. Refer to the diagnostic functional test Troubleshooting, "Start Relay Circuit - Test" for information that is related to troubleshooting the circuit for the SMMS.

Circuit protection is provided by circuit breakers for the ECM relay, the SMMS, and the emergency stop switch.

Illustration 1	g02511311
Schematic for the electrical power supply (typical example)

Test Step 1. Inspect the Electrical Connectors and the Wiring

1. Remove electrical power from the ECM.
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   Illustration 2	g01206567
   Location of the J1/P1 and the J2/P2 ECM connectors (typical engine view) (1) J2/P2 ECM connector (2) J1/P1 ECM connector

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   Illustration 3	g01207955
   Location of the engine interface connector (typical engine view) (3) Engine interface connector

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   Illustration 4	g01206446
   Location of the battery isolator switch, the ECM relay, and the starting motor magnetic switch (typical left side engine view) (4) Battery disconnect switch (5) ECM relay (6) Starting motor magnetic switch

2. Thoroughly inspect connectors (1), (2), and (3). Also, thoroughly inspect the connectors for switches (4) and (6) and for relay (5). Refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect" for details.
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   Illustration 5	g01206553
   P2 ECM connector (P2-59) SMMS (P2-60) Digital return

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   Illustration 6	g01206554
   P1 ECM connector (P1-48) +Battery (P1-52) +Battery (P1-53) +Battery (P1-55) +Battery (P1-57) +Battery (P1-61) −Battery (P1-63) −Battery (P1-65) −Battery (P1-67) −Battery (P1-69) −Battery (P1-70) Keyswitch

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   Illustration 7	g01207957
   Terminal locations for the engine interface connector (Terminal 4) +Battery (Terminal 23) Relay control

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   Illustration 8	g01207940
   Terminal locations for the ECM relay and the connector (typical example) (4) ECM relay (Terminal 1) +Battery (Terminal 2) Relay ground (Terminal 3) Electrical power to the ECM (Terminal 5) Relay control

3. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connectors and the connector for the ECM relay.

4. Check the torque of the allen head screws for the ECM connectors. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.

5. Check the harness and the wiring for abrasion and for pinch points from the batteries to the ECM.

Expected Result:

All connectors, pins, and sockets are completely coupled and/or inserted, and the harness and wiring are free of corrosion, of abrasion and of pinch points.

Results:

• OK - The connectors and wiring appear to be OK. Proceed to Test Step 2.

• Not OK - The connectors and/or wiring are not OK.

  Repair: Repair the wiring and/or the connectors. Replace parts, if necessary. Verify that the original problem has been resolved.

  STOP

Test Step 2. Check the Battery Voltage at the ECM

1. Disconnect the J1/P1 ECM connector.

2. Restore electrical power to the ECM.

3. Measure the voltage between P1-48 (+Battery) and P1-61 (−Battery).

4. Measure the voltage between P1-52 (+Battery) and P1-63 (−Battery).

5. Measure the voltage between P1-53 (+Battery) and P1-65 (−Battery).

6. Measure the voltage between P1-55 (+Battery) and P1-67 (−Battery).

7. Measure the voltage between P1-57 (+Battery) and P1-69 (−Battery).

8. Measure the voltage between P1-70 (keyswitch) and P1-63 (−Battery).

9. Remove eletrical power to the ECM.

Expected Result:

The measured voltage is between 22.0 VDC and 27.0 VDC.

Results:

• OK - The measured voltage is between 22.0 VDC and 27.0 VDC.

  Repair: The ECM is receiving the correct voltage. There may be an intermittent problem in the harness or in a connector. If an intermittent condition is suspected, refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect" for details.

  STOP

• Not OK - The voltage is not correct at the ECM. There is a problem with the electrical power supply circuit. Leave the J1/P1 ECM connectors disconnected. Proceed to Test Step 3.

Test Step 3. Check the Batteries

1. Measure the no-load battery voltage at the battery posts.

   The correct voltage is between 22.0 VDC and 27.0 VDC.

2. Load test the batteries. Use the 4C-4911 Battery Load Tester. Refer to the Operating Manual, SEHS9249. Refer to Special Instruction, SEHS7633 for details.

Expected Result:

The batteries pass the load test.

Results:

• OK - The batteries pass the load test. There is a problem in the harness between the batteries and the ECM. There may be a problem in the circuit for the ECM relay. Proceed to Test Step 6.

• Not OK - The batteries failed the load test.

  Repair: The batteries are the cause of the original problem. There may be a problem with the alternator. Recharge the batteries or replace the batteries. Restore the wiring to the original configuration.

  If a problem with the alternator is suspected, refer to Troubleshooting, "Alternator".

  STOP

Test Step 4. Check the Voltage from the ECM Relay to the ECM

1. Remove electrical power to the ECM.

2. Disconnect the connector from the ECM relay.

3. Remove the wire from the terminal location 3 of the connector for the ECM relay.

4. Fabricate a jumper wire that is long enough to provide a test circuit for a terminal location at the ECM relay. Crimp a spade terminal to one end of the jumper wire.

5. Install the jumper wire into terminal location 3 of the connector for the ECM relay. Connect the connector to the ECM relay.

6. Restore electrical power to the ECM. Ensure that the emergency stop switch is in the RUN position.

7. Measure the voltage between the loose end of the jumper wire and engine ground.

8. Remove electrical power to the ECM.

Expected Result:

Voltage is present on terminal 3 at the ECM relay.

Results:

• OK - Voltage is present on terminal 3 at the ECM relay.

  Repair: If voltage is present on terminal 3, there is a problem in the harness between the ECM relay and the ECM. Repair the harness and/or the connectors. Replace parts, if necessary.

  STOP

• Not OK - Voltage is not present on terminal 3 at the ECM relay. There is a problem in the harness between the ECM relay and the batteries. There may be a problem with the relay. Proceed to Test Step 6.

Test Step 5. Check for +Battery Voltage at the ECM Relay

1. Disconnect the connector from the ECM relay.

2. Restore electrical power to the ECM.

3. Measure the voltage between terminal 1 at the connector for the ECM relay and the engine ground stud.

Expected Result:

The measured voltage is 24 ± 3 VDC.

Results:

• OK - The voltage is 24 ± 3 VDC. The proper voltage is reaching terminal 1 of the ECM relay. Check the circuit for the relay control for the proper operation. Leave the connector for the ECM relay disconnected. Proceed to Test Step 7.

• Not OK - The voltage is not 24 ± 3 VDC.

  Repair: There is an open circuit in the harness or in a connector between the batteries and the ECM relay. Ensure that the circuit breaker for the ECM relay has not tripped. Repair the wiring and/or the connectors. Replace parts, if necessary. Verify that the original problem has been resolved.

  STOP

Test Step 6. Check the Voltage for the Relay Control at the ECM Relay

1. Check that the battery disconnect switch is in the ON position. Ensure that the emergency stop switch is in the RUN position.

2. Measure the voltage between terminals 2 (relay ground) and 5 (relay control) at the connector for the ECM relay.

   A correct measurement will indicate that no voltage is present between the terminals.

3. Place the emergency stop switch in the STOP position.

4. Again, measure the voltage between terminals 2 (relay ground) and 5 (relay control) at the connector for the ECM relay.

   A correct measurement will indicate that the voltage is 24 ± 3 VDC between the terminals.

Expected Result:

The voltage is correct between connector terminals for each position of the emergency stop switch.

Results:

• OK - The voltage is correct for each position of the emergency stop switch. The circuit for the relay control is operating correctly. The problem may be the ECM relay or the problem may be in the ground circuit from the batteries to the ECM. Leave the connector for the ECM relay disconnected. Proceed to Test Step 7.

• Not OK - One of the following conditions exists: Voltage is present at the terminals with the emergency stop switch in the RUN position. Voltage is not present at the terminals with the emergency stop switch in the STOP position.

  Repair: There is a problem in the circuit for the emergency stop switch. Repair the circuit and retest the electrical power supply circuit. Refer to the diagnostic functional test Troubleshooting, "Emergency Stop Circuit - Test".

  STOP

Test Step 7. Test the Ground Circuit

1. Ensure that the electrical power is restored to the ECM.

2. Measure the voltage between the battery's +Battery terminal and the following test points. If voltage is not present at a test point, the problem is in the wire or in the connector that precedes the point in the circuit. Refer to Illustration 1 as a reference.
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   Table 2

   Device	Test location
   Battery disconnect switch	Input terminal
   	Output terminal
   Starting motor	−Battery terminal
   P1 ECM connector	Terminal 61
   	Terminal 63
   	Terminal 65
   	Terminal 67
   	Terminal 69
   Connector for the ECM relay	Terminal 2

Expected Result:

A voltage of 24 VDC is measured between the +Battery and each test location in Table 2.

Results:

• OK - A voltage of 24 VDC is measured for each test location.

  Repair: The wiring for the ground circuit is OK. The problem is an open circuit in the ECM relay. Replace the ECM relay. Verify that the original problem has been resolved.

  STOP

• Not OK - A voltage of 24 VDC is not present at one of the test locations.

  Repair: There is an open circuit in the harness or in the connector that precedes this test location. Repair the wiring and/or the connectors. Replace parts, if necessary. Verify that the original problem has been resolved.

  STOP