C175-16 Locomotive Engine Caterpillar

Use this procedure to troubleshoot the electrical system if a problem is suspected with the power to the engines Electronic Control Module (ECM) or if any one of the diagnostic codes or the event code in Table 1 is active or easily repeated.

Table 1

Diagnostic Codes Table
Description	Conditions which Generate this Code	System Response
168-0 Battery Potential / Power Input #1 : High - most severe (3)	The battery supply voltage is greater than 32 VDC for two seconds. The engines ECM has been powered for three seconds. The engine is not being cranked.	The code is logged.
168-1 Battery Potential / Power Input #1 : Low - most severe (3)	The battery supply voltage is less than 9 VDC for two seconds. The engines ECM has been powered for three seconds. The engine is not being cranked.
168-2 Battery Potential / Power Input #1 : Erratic, Intermittent, or Incorrect	The engine is running. The battery voltage falls below 9 VDC for one second. The voltage returns above 9 VDC. or Three voltage readings in the last seven seconds were below 9 VDC.
1834-2 Ignition Key Switch loss of signal	The ECM detects at least three changes to the state of the signal that is for the keyswitch in the last one second.	The code is logged.

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 action does not indicate a problem in the wiring at the ECM. Verify that there are no problems with the starting system or with the charging system before you use this test.

Unswitched battery voltage is supplied through the machine connector to the ECM. The voltage is supplied to terminals at P1-48, P1-52, P1-53, P1-55, and P1-57 of the ECM connector. The negative battery is supplied to the ECM at P1-61, P1-63, P1-65, P1-67, and P1-69. The ECM receives battery voltage from the keyswitch at P1-70 when the keyswitch is in the ON position or in 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 engine ECM requires the keyswitch to be in the ON position in order to maintain communications with Caterpillar Electronic Technician (ET).

Illustration 1	g03324577
Typical schematic of the electrical power supply

Illustration 2	g03324690
Locations of the connectors at the ECM that are for the 16 cylinder engines (typical front engine view) (1) Connector for the right-hand rail (2) J1/P1 ECM connectors (3) J2/P2 ECM connector (4) Engine interface connector at the control box (4) Connector for the front harness

Illustration 3	g01323936
Terminal locations at the P1 ECM connector for the electrical power supply (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 circuit

Illustration 4	g01324119
Terminal locations at the connector for the fuel control valve that are for the electrical power supply (Terminal 8) Keyswitch circuit

Table 2

Troubleshooting Test Steps	Values	Results
1. Inspect the Electrical Connectors and the Wiring A. Turn the battery disconnect switch to the OFF position. B. Thoroughly inspect connectors (1) through (2) and (3) through (4). Inspect the wiring for the crossover harness that is in the control box for abrasion. Also check the condition of the circuit breakers in the low current and high current power distribution panels. Ensure that the breakers are in good repair and are not tripped. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the proper procedure for inspecting system wiring. C. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the circuit. D. Check the ECM connector (allen head screw) for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details. E. Check the harness and the wiring for abrasion and for pinch points. F. Check each of the fuses at the low current power distribution panel that are associated with the circuit. At the high current power distribution panel, ensure that the main circuit breaker has not been thrown. Note: Replace any fuses that are blown. If necessary, reset the main circuit breaker.	Connectors	Results: The harness and wiring are OK. Proceed to Test Step 2 Results: There is a problem in the connectors and/or wiring. 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 coupled. Verify that the repair eliminates the problem.
2. Check the Voltage at the Battery Post A. Measure the voltage across the battery posts.	24 ± 3 VDC.	Results: The voltage is 24 ± 3 VDC. Proceed to Test Step 3 Results: The voltage is not 24 ± 3 VDC. Repair: There is a problem with the batteries or the charging system. Refer to Systems Operation/Testing and Adjusting for information that is related to troubleshooting the charging system. Verify that the repair eliminates the problem.
3. Check the Voltage at the ECM Connector A. Disconnect the J1/P1 ECM connectors. B. Measure the voltage between P1-48 (unswitched +Battery) and P1-61 (−Battery). C. Measure the voltage between P1-52 (unswitched +Battery) and P1-63 (−Battery). D. Measure the voltage between P1-53 (unswitched +Battery) and P1-65 (−Battery). E. Measure the voltage between P1-55 (unswitched +Battery) and P1-67 (−Battery). F. Measure the voltage between P1-57 (unswitched +Battery) and P1-69 (−Battery). G. Turn the keyswitch to the ON position. H. Measure the voltage between P1-70 (keyswitch) and P1-69 (−Battery). I. Turn the keyswitch to the OFF position.	ECM Connector	Results: OK - All of the voltage measurements are within the range that is specified. Repair: The ECM is receiving the correct voltage. There may be an intermittent problem in a connector or in the harness wiring. If an intermittent condition is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect" for information that is related to troubleshooting intermittent problems. Results: Not OK - Keyswitch voltage out of range. The voltage for the keyswitch is not within the range that is specified. Results: Not OK - Voltage to the ECM is out of range. The voltage for the ECM is not within ± 1 VDC of the voltage that was measured at the battery terminals. Repair: The voltage is not correct at the ECM. There is an open circuit or excessive resistance in the wiring or connections between the batteries and the ECM. Verify that the fuse for the ECM is not blown. Verify that the battery disconnect switch is in the RUN position. Verify that the connection for the engine ground is clean and tight. Repair the connectors or wiring and/or replace the connectors or wiring.
4. Check for Proper Operation of the Keyswitch A. Turn the battery disconnect switch to the OFF position. B. Fabricate a jumper wire that is long enough to create a test circuit at the connector for the keyswitch. Crimp a connector socket to one end of the jumper wire. C. Disconnect the connector at the keyswitch. D. Use a wire removal tool to remove the wire from terminal location 1 on the harness side of the connector for the keyswitch. Install the jumper wire into this terminal location. Note: Ensure that the loose end of the jumper wire does not come into contact with any ground source. E. Turn the battery disconnect switch to the RUN position. F. Turn the keyswitch to the ON position. G. Measure the voltage between the loose end of the jumper wire and a good source of ground. H. Turn the battery disconnect switch to the OFF position. Turn the keyswitch to the OFF position. I. Restore all of the wiring to the original configuration.	Keyswitch	Results: OK - Battery voltage is present on terminal 1 of the connector for the keyswitch. Repair: Battery voltage is present on the keyswitch circuit at the connector for the keyswitch, but battery voltage is not present on the keyswitch circuit at the ECM. There is a problem in the harness or in a connector between the keyswitch and the ECM. Locate the problem in the harness or in a connector. Verify that the original problem has been resolved. Results: Not OK - Battery supply voltage is not present at the connector for the keyswitch. There is a problem in the battery circuit for the keyswitch. There may be a problem with the keyswitch. Proceed to Test Step 5
5. Check for Battery Voltage at the Keyswitch A. Turn the battery disconnect switch to the OFF position. B. Disconnect the connector at the keyswitch. C. Turn the battery disconnect switch to the RUN position. D. Measure the voltage between terminal 4 of the connector at the keyswitch and a good source of ground. E. Turn the battery disconnect switch to the OFF position.	Voltage at the Keyswitch	Results: OK - Battery voltage is present on terminal 4 at the connector for the keyswitch. Repair: Voltage is present at the battery terminal for the keyswitch, but voltage is not present at the output of the keyswitch. There is a problem with the keyswitch. Replace the keyswitch. Verify that the original problem has been resolved. Results: Not OK - Battery voltage is not present on terminal 4 at the connector for the keyswitch. Repair: If voltage is not present on terminal 4, ensure that the fuse is in good repair. Check the harness between the connector for the keyswitch and the fuse panel and check the harness between the fuse panel and the main power relay. Ensure that battery voltage is present at the main power relay. Perform the necessary repairs. Verify that the original problem has been eliminated.