G3520B Industrial Engine Caterpillar

Electrical power is supplied to the following components:

• Master Electronic Control Module (ECM)

• Slave ECM

• Integrated Temperature Sensing Module (ITSM)

• Fuel metering valve

• Throttle actuator

• Actuator for the bypass valve

• Optional control panel

The cause of an intermittent power supply can occur on either the positive side or the negative side of the power supply.

The 24 VDC power supply for the engine can be provided by a battery or by an electrical power supply. The minimum requirement for the power supply is 22 VDC at 16 amperes.

The components are electrically protected by five fuses that are located in a junction box on the left side of the engine.

The master ECM input at terminal 70 of the P1 connector ("Switched +Battery") receives battery voltage from the engine control when the control is in the START mode, in the STOP mode, or in the AUTO mode. When the master ECM detects battery voltage at this input, the master ECM will power up. When battery voltage is removed from this input, the master ECM will power down after the engine has shut down.

The input for the slave ECM at terminal 70 of the P3 connector ("Switched +Battery") receives battery voltage from the engine control when the control is in the START mode, in the STOP mode, or in the AUTO mode. When the slave ECM detects battery voltage at this input, the slave ECM will power up.

The actuator for the bypass valve and the throttle actuator receive electrical power via dedicated fuses. When electrical power is applied to the engine, the actuators receive electrical power. However, the actuators are in sleep mode. Sleep mode significantly reduces the electrical power consumption of the actuators.

When the engine control is not in the OFF/RESET mode, switched +Battery is applied to two relays that are inside the terminal box for the master ECM. The relays become energized. The relay's contacts complete a circuit. The completed circuit disables the sleep mode.

The "168-02" diagnostic code indicates that the voltage of the power supply is intermittent or low while the engine is running. If the supply voltage drops to zero and stays at zero, the master ECM will not log this code. The engine will shut down.

The "336-02" diagnostic code indicates that the master ECM has detected a problem with the circuit for the engine control switch.

Logged diagnostic codes provide a historical record. Before you begin this procedure, use the Caterpillar Electronic Technician (ET) to print the logged codes to a file.

This procedure may generate additional diagnostic codes. Keep your mind on correcting the cause of the original diagnostic code. Clear the diagnostic codes after the problem is resolved.

Illustration 1	g01089803
Schematic for the electrical power supply

Test Step 1. Inspect the Electrical Connectors and Wiring

1. Set the engine control to the OFF/RESET mode. Remove the electrical power from the engine.

Note: For the following steps, refer to Troubleshooting, "Inspecting Electrical Connectors".

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Illustration 2	g01089181
Terminal box for the master ECM (1) J1/P1 connectors for the master ECM (2) J5/P5 connectors for the customer's connections (3) J8/P8 connectors for the wiring to the actuators and the slave ECM (4) Relay for the actuator for the bypass valve (5) Relay for the throttle actuator (6) J10/P10 connectors for the harness to the optional control panel

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Illustration 3	g01089189
Terminal box for the slave ECM (7) J3/P3 connectors for the slave ECM (8) J11/P11 connectors for the harness to the master ECM

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Illustration 4	g01089196
Junction box (9) 20 amp fuse for the throttle actuator (10) 15 amp fuse for the actuator for the actuator for the compressor bypass (11) 15 amp fuse for the electronic control modules, the MIDS, and the service tool (12) 6 amp fuse for the fuel metering valve (13) 6 amp fuse for the keyswitch and the integrated temperature sensing module (14) Connection for the -Battery to the throttle actuator (15) Connection for the -Battery to the actuator for the compressor bypass (16) Connection for the +Battery from the power supply (17) Connection for the -Battery to the fuel metering valve (18) Connection for the -Battery to the electronic control modules, the MIDS, and the service tool (19) Connection for the -Battery to the electronic control modules, the MIDS, and the service tool (20) Connection for the -Battery from the power supply

4. Thoroughly inspect the following connections:
   • Electrical connections to each fuse

   • Connectors for the 24 VDC power supply

   • Connectors for the engine control switch

   1. Check the torque of the allen head screw for the ECM connectors. The proper torque is 6 ± 1 N·m (55 ± 9 lb in).
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   Illustration 5	g00995688
   ECM connectors P1 and P3 (52) Unswitched +Battery (53) Unswitched +Battery (55) Unswitched +Battery (57) Unswitched +Battery (63) -Battery (65) -Battery (67) -Battery (69) -Battery (70) Switched +Battery

   2. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the electrical power supply.

   3. Check the harness and wiring for abrasion and pinch points from the power supply to the master ECM and from the engine control switch to the master ECM.

   4. Check the harness and wiring for abrasion and pinch points from the master ECM to the slave ECM.

Expected Result:

The connectors, pins, and sockets are connected properly. The connectors and the wiring do not have corrosion, abrasion, or pinch points.

Results:

• OK - The components are in good condition with proper connections. Proceed to Test Step 2.

• Not OK - The components are not in good condition and/or at least one connection is improper.

  Repair: Perform the necessary repairs and/or replace parts, if necessary. Ensure that all of the seals are properly installed. Make sure that the connectors are properly fastened. Verify that the repair has eliminated the problem.

  Stop.

Test Step 2. Check the Voltage at the Power Supply, at the Master ECM, and at the Slave ECM

1. Make sure that the engine will not crank during this procedure. Make sure that the pressurized air supply is OFF. Make sure that the air is purged from the system.

Note: If a power supply is used instead of batteries, the minimum voltage for the power supply is 22 VDC at 16 amperes. Troubleshoot the power supply if the voltage is less than 22 VDC or more than 29 VDC.

2. Measure the voltage at the terminals for the power supply. Record the measurement.

3. Insert two 7X-1710 Multimeter Probes into the harness side of the P1 connector. Insert the first probe into terminal 52. Insert the second probe into terminal 63. Connect a multimeter to the probes.

4. Measure the power supply voltage at the P1 connector. During the measurement, wiggle the harness in order to check for an intermittent problem. Be sure to wiggle the harness near each of the connections. Record the measurement.

5. Insert two 7X-1710 Multimeter Probes into the harness side of the P3 connector. Insert the first probe into terminal 52. Insert the second probe into terminal 63. Connect a multimeter to the probes.

6. Measure the power supply voltage at the P3 connector. During the measurement, wiggle the harness in order to check for an intermittent problem. Be sure to wiggle the harness near each of the connections. Record the measurement.

Expected Result:

The voltage that is measured at the terminals for the power supply is at least 22 VDC. The voltage that is measured at the P1 connector and at the P3 connector is within 2 volts of the voltage that was measured at the terminals for the power supply. The voltage measurements are constant.

Results:

• OK - Each ECM is receiving the correct voltage. Proceed to Test Step 3.

• Not OK - An ECM is not receiving the correct voltage.

  Repair: Use a voltmeter to check the wiring. Refer to the schematic diagram for the electrical system. Locate the source of the voltage drop. Make repairs, as needed.

  Stop.

Test Step 3. Check the Engine Control

1. Make sure that the engine will not crank during this procedure. Make sure that the pressurized air supply is OFF. Make sure that the air is purged from the system.

2. Connect Cat ET to the service tool connector. Refer to Troubleshooting, "Electronic Service Tools".

Note: An "E225 Engine Overcrank" and/or an "E233 Low Engine Prelube Pressure" event code may be generated during this step. After you have completed this step, clear the events from the "Logged Events" screen of Cat ET.

3. Observe the "Active Diagnostic" screen on Cat ET and set the engine control to the STOP mode, the START mode, and the AUTO mode. Look for an active "336-02 Incorrect ECS Switch inputs" diagnostic code. Repeat this step several times.

Expected Result:

A "336-02 Incorrect ECS Switch inputs" diagnostic code was not activated when the engine control was set to the STOP mode, to the START mode, and to the AUTO mode.

Results:

• OK - A "336-02 Incorrect ECS Switch inputs" diagnostic code was not activated. The inputs from the engine control switch are correct. The problem seems to be resolved.

  Repair: The problem may be intermittent. Refer to Troubleshooting, "Inspecting Electrical Connectors".

  Stop.

• Not OK - A "336-02 Incorrect ECS Switch inputs" diagnostic code was activated. The master ECM has detected an invalid pattern from the engine control. Proceed to Test Step 4.

Test Step 4. Check the Circuit of the Engine Control

1. Make sure that the engine will not crank during this procedure. Make sure that the pressurized air supply is OFF. Make sure that the air is purged from the system.

2. Set the engine control to the OFF/RESET mode.

3. Insert two 7X-1710 Multimeter Probes into the harness side of the P1 connector. Insert the first probe into terminal 31. Insert the second probe into terminal 61. Connect a multimeter to the probes.

Note: An "E225 Engine Overcrank" and/or an "E233 Low Engine Prelube Pressure" event code may be generated during the test. After you have completed the test, clear the events from the "Logged Events" screen of Cat ET.

Note: During these measurements, wiggle the harness in order to check for an intermittent problem. Be sure to wiggle the harness near each of the connections.

4. Set the engine control to the STOP mode and measure the voltage between terminals P1-31 and P1-61. The correct voltage measurement is less than one volt.

5. Remove the probe from terminal 61 and insert the probe into terminal 62.

6. Set the engine control to the START mode and measure the voltage between terminals P1-31 and P1-62. The correct voltage measurement is less than one volt.

7. Remove the probe from terminal 62 and insert the probe into terminal 64.

8. Set the engine control to the AUTO mode and measure the voltage between terminals P1-31 and P1-64. The correct voltage measurement is less than one volt.

9. Remove the probe from terminal 31 and insert the probe into terminal 69. Remove the probe from terminal 64 and insert the probe into terminal 70.

10. Set the engine control to the STOP mode and measure the voltage between terminals P1-69 and P1-70 connector. The correct voltage measurement is at least 20 VDC.

11. Set the engine control to the START mode and measure the voltage between terminals P1-69 and P1-70. The correct voltage measurement is at least +20 VDC.

12. Set the engine control to the AUTO mode and measure the voltage between terminals P1-69 and P1-70. The correct voltage measurement is at least 20 VDC.

Expected Result:

The voltage checks are within the specifications.

Results:

• OK - The voltage checks are within the specifications. Remove the probes from the P1 connector. Start the engine and run the engine. If the original problem is not resolved, the master ECM may have a problem.

  Repair: It is unlikely that the master ECM has failed. Perform the following procedure:Temporarily install a new master ECM. Refer to Troubleshooting, "Replacing the ECM".If the problem is resolved with the new ECM, install the original ECM and verify that the problem returns. If the new ECM operates correctly and the original ECM does not operate correctly, replace the ECM. Refer to Troubleshooting, "Replacing the ECM".

  Stop.

• Not OK - The P1 connector does not have the correct voltage.

  Repair: Perform the following steps:

  1. Set the engine control to the OFF/RESET mode. Remove the electrical power from the engine.

  2. Disconnect the wires for the STOP, START, and AUTO modes from the engine control.

  3. Use an ohmmeter to check the contacts for the engine control. Set the control to each position in order to check the contacts.

  4. If the engine control is faulty, replace the control. If the problem is not resolved, repair the harness, when possible. Replace the harness, if necessary.

  Stop.