C7 and C9 Marine Engines Caterpillar

Use this test to troubleshoot any suspect problems with power to the Electronic Control Module (ECM).

This procedure covers the following diagnostic codes:

• 168-00 "System Voltage High"

• 168-01 "System Voltage Low"

• 168-02 "System Voltage intermittent/erratic"

Use this test if there are intermittent engine shutdowns or if a difficulty in starting is not accompanied by loss of electrical accessories. Engine shutdowns that are accompanied by a loss of other electrical accessories indicate a problem in the keyswitch. This does not indicate a problem in the wiring at the engine's ECM. Verify that there are no problems with the starting system or the charging system before you use this test.

Unswitched battery voltage is supplied through the J61/P61 machine connector to the ECM at P1-48, P1-52, and P1-53. The negative battery is supplied to the ECM at P1-61, P1-63, and P1-65. The ECM receives the input from the keyswitch at P1-70 when the keyswitch is in the ON position or the START position. When the ECM detects battery voltage at this input, the ECM will power up. When battery voltage is removed from this input, the ECM will power down. The ECM continuously receives battery voltage through the 20 Amp fuse for the ECM.

The engine ECM requires the keyswitch to be in the ON position in order to maintain communications with the electronic service tool.

Illustration 1	g01230328
Schematic

Illustration 2	g01231248
(22) Engine shutdown switch (P1-48) +Battery (P1-52) +Battery (P1-53) +Battery (P1-61) −Battery (P1-63) −Battery (P1-65) −Battery (P1-67) −Battery (P1-70) Keyswitch

Test Step 1. Inspect Electrical Connectors and Wiring

1. Turn the remote shutdown switch to the OFF position.

2. Remove the electrical power from the ECM.

3. Thoroughly inspect the ECM connectors J1/P1 and J2/P2. Inspect all of the connectors that are associated with this circuit. Refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect".

4. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the circuit.

5. Check the ECM connector (allen head screw) for the proper torque. Refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect".

6. Check the harness and the wiring for abrasion and for pinch points.

Expected Result:

All connectors, pins, and sockets are completely inserted and coupled. The harness and wiring are free of corrosion, of abrasion, and of pinch points. All connections and grounds are tight and free of corrosion.

Results:

• OK - The harness and wiring are OK. Proceed to Test Step 2.

• Not OK - There is a problem in the connectors and/or wiring.

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are completely coupled.Verify that the repair eliminates the problem.

  STOP

Test Step 2. Check the Battery Voltage at the ECM

1. Turn the remote shutdown switch to the ON position.

2. Disconnect the J1/P1 ECM connector.

3. Restore the electrical power to the ECM.

4. Measure the voltage between P1-48 (Unswitched Positive Battery) and P1-61 (Negative Battery).

5. Measure the voltage between P1-52 (Unswitched Positive Battery) and P1-63 (Negative Battery).

6. Measure the voltage between P1-53 (Unswitched Positive Battery) and P1-65 (Negative Battery).

7. Measure the voltage between P1-53 (Unswitched Positive Battery) and P1-67 (Negative Battery).

8. Measure the voltage between P1-70 (Keyswitch) and P1-63 (Negative Battery).

Expected Result:

The measured voltage is between 11.0 VDC and 13.5 VDC for a 12 volt system and between 22.0 VDC and 27.0 VDC for a 24 volt system with no suspected intermittent problems at this time.

Results:

• OK - The ECM is receiving the correct voltage.

  Repair: If an intermittent condition is suspected, refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect".

  STOP

• Not OK - The voltage is not correct at the ECM. Proceed to Test Step 3.

• Keyswitch voltage out of range - Proceed to Test Step 4.

Test Step 3. Check the Batteries

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

2. Load test the batteries. Use the 4C-4911 Battery Load Tester. Refer to Special Instruction, SEHS9249, "Use of 4C-4911 Battery Load Tester for 6, 8 and 12 Volt Lead Acid Batteries" and Special Instruction, SEHS7633, "Battery Test Procedure".

Expected Result:

The batteries pass the load test. The measured voltage is the minimum specification for a 12V or 24V system.

Results:

• OK - The batteries are OK.

  Repair: There is an open circuit or excessive resistance in the wiring or connections between the batteries and the ECM. Verify that the 20 Amp fuse for the ECM is not blown. Check the connections at the customer connector. Verify that the connection for the engine ground is clean and tight and that the battery disconnect switch is functioning properly. Repair the connectors or wiring and/or replace the connectors or wiring.

  STOP

• Not OK - The battery voltage is low or the battery did not pass the load test.

  Repair: Recharge or replace the faulty batteries. Verify that the repair eliminates the problem.

  STOP

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

1. Remove the electrical power from the ECM.

2. Remove the wire from the terminal R of the keyswitch.

3. Restore the electrical power to the ECM.

4. Measure the voltage on terminal B of the keyswitch to engine ground.

5. Measure the voltage on terminal R of the keyswitch to engine ground.

6. Remove the electrical power from the ECM.

Expected Result:

Voltage is present on terminal B and terminal R at the keyswitch.

Results:

• OK - Voltage is present on terminal B and terminal R at the keyswitch.

  Repair: If voltage is present on terminal R, repair the wire between the keyswitch and the ECM. Verify that the problem is eliminated.

  STOP

• Not OK - Voltage is not present on terminal B at the keyswitch.

  Repair: If voltage is not present on terminal B, repair the wire between the +Battery and the keyswitch. Verify that the fuse for the keyswitch is not blown. Verify that the problem is eliminated.

  STOP

• Not OK - Voltage is not present on terminal R at the keyswitch.

  Repair: If voltage is present on terminal B of the keyswitch but not present on terminal R, replace the keyswitch. Return all wiring to the original configuration. Verify that the problem is eliminated.

  STOP