Use this test to troubleshoot any suspect problems with power to the Electronic Control Module (ECM).
Use this procedure in order to troubleshoot the 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 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 P1-70 receives switched battery voltage through the main relay which is controlled by the keyswitch. When the keyswitch is in the ON position or in the START position the main relay is energized. 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 15 Amp circuit breaker for the ECM.
The engine ECM requires the keyswitch to be in the ON position in order to maintain communications with Caterpillar Electronic Technician (ET).
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| Illustration 1 | g01280337 |
Schematic for the electrical power supply circuit | |
Test Step 1. Inspect the Electrical Connectors and the Wiring
- Remove electrical power from the engine ECM.
- Thoroughly inspect the J1/P1 ECM connectors. Inspect all of the connectors that are in the circuit. Refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect" for details.
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| Illustration 2 | g01183529 |
Location of the J1/P1 ECM connectors | |
- Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the circuit.
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| Illustration 3 | g01112632 |
P1 connections for the electrical power supply circuit (P1-48) +Battery (P1-52) +Battery (P1-53) +Battery (P1-61) −Battery (P1-63) −Battery (P1-65) −Battery (P1-70) Keyswitch | |
- Check the allen head screw for each of the ECM connectors for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.
- 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 appear to be 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
- Remove electrical power from the engine ECM.
- Disconnect the J1/P1 ECM connector.
- Restore electrical power to the engine ECM.
- Measure the voltage between P1-48 (Unswitched +Battery) and P1-61 (−Battery).
- Measure the voltage between P1-52 (Unswitched +Battery) and P1-63 (−Battery).
- Measure the voltage between P1-53 (Unswitched +Battery) and P1-65 (−Battery).
- Measure the voltage between P1-70 (Keyswitch) and P1-63 (−Battery).
Expected Result:
The measured voltage is between 22 VDC and 27 VDC.
Results:
- OK - The ECM is receiving the correct voltage.
Repair: There may be an intermittent electrical problem in a harness or in a connector. If an intermittent condition is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect".
STOP
- Unswitched power out of range - The voltage is not correct for one of the unswitched battery circuits at the ECM. Proceed to Test Step 3.
- Keyswitch voltage out of range - The voltage is not correct for the keyswitch circuit at the ECM. Proceed to Test Step 4.
Test Step 3. Check the Batteries
- Measure the no-load battery voltage at the battery posts.
- 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 24V system.
Results:
- OK - The batteries pass the load test.
Repair: The batteries are OK. There is an open circuit or excessive resistance in the wiring or connections between the batteries and the ECM. Verify that the circuit breaker for the ECM is not tripped. Verify that the connection at the engine ground stud 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 at the Keyswitch
- Remove electrical power from the engine ECM.
- Remove the wire from the terminal R of the keyswitch.
- Restore electrical power to the engine ECM.
- Measure the voltage on terminal B of the keyswitch to engine ground.
- Measure the voltage on terminal R of the keyswitch to engine ground.
- Remove electrical power from the engine 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. Proceed to Test Step 5.
- Not OK - Voltage is not present on terminal B at the keyswitch.
Repair: If voltage is not present on terminal B, repair the circuit between the +Battery and the keyswitch. Check the circuit protection for the circuit. 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
Test Step 5. Check the Voltage from the Main Relay to the Fuse for the Engine Control
- Remove electrical power from the engine ECM.
- Remove the wire 112-PU from the normally open terminal of the main relay.
- Restore electrical power to the engine ECM.
- Turn the keyswitch to the ON position.
- Measure the voltage between the normally open terminal of the main relay and engine ground.
- Turn the keyswitch to the OFF position.
- Remove electrical power from the engine ECM.
- Reconnect all wires to the original configuration.
Expected Result:
The voltage measures 24 ± 3.0 VDC.
Results:
- OK - The voltage measures 24 ± 3.0 VDC.
Repair: Verify that the 15 Amp fuse for the ECM is not blown. Repair the wire between the main relay and the fuse for the engine control or repair the wire between the fuse for the engine control and the ECM connector P1.
STOP
- Not OK - The voltage does not measure 24 ± 3.0 VDC. 6
Test Step 6. Check the Voltage at the Main Relay
- Remove electrical power from the engine ECM.
- Remove the wire 308-YL from the coil of the main relay.
- Remove the wire 101-RD from the normally open contact of the main relay.
- Restore electrical power to the engine ECM.
- Turn the keyswitch to the ON position.
- Measure the voltage between wire 308-YL and engine ground.
- Measure the voltage between wire 101-RD and engine ground.
- Remove electrical power from the engine ECM.
- Reconnect all wires to the original configuration.
Expected Result:
The voltage measures 24 ± 3.0 VDC.
Results:
- OK - The voltage measures 24 ± 3.0 VDC on both wires.
Repair: Verify that the wire 200-BK has continuity to engine ground. If wire 200-BK is OK, replace the main relay. Verify that the problem is no longer present.
STOP
- Not OK - The voltage does not measure 24 ± 3.0 VDC on wire 101-RD.
Repair: Repair the wire between the main relay and the battery.
STOP
- Not OK - The voltage does not measure 24 ± 3.0 VDC on wire 308-YL.
Repair: Repair the wire between the main relay and terminal R of the keyswitch.
STOP