C11 and C13 Engines for Caterpillar Built Machines Electrical Power Supply Circuit - Test Caterpillar

System Operation Description:

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.

The ECM receives battery voltage through the main relay and the 15 Amp fuse for the engine control. Switched 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 receives the input 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 on P1-70, the ECM will power up. When battery voltage is removed from P1-70, the ECM will power down.

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

Illustration 1	g01119726
Typical schematic

Illustration 2	g01112632
P1 ECM connections (P1-48) +Battery (P1-52) +Battery (P1-53) +Battery (P1-61) −Battery (P1-63) −Battery (P1-65) −Battery (P1-70) Keyswitch

Test Step 1. Inspect Electrical Connectors and Wiring

1. Turn OFF the power to the ECM.

2. Thoroughly inspect the ECM connectors J1/P1 and J2/P2. Refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect" for details.

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

4. Check the ECM connector (allen head screw) for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

5. 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. Disconnect the J1/P1 ECM connector.

2. Turn ON the power to the ECM.

3. Turn the keyswitch to the ON position.

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

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

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

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

8. Turn the keyswitch to the OFF position.

Expected Result:

The voltage measures 24 ± 3.0 VDC.

Results:

• OK - The ECM is receiving the correct voltage.

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

  STOP

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

• Not OK - Keyswitch - The voltage is not correct at the input for the keyswitch. 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. Proceed to Test Step 4.

• 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

1. Turn OFF the power to the ECM.

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

3. Turn ON the power to the ECM.

4. Turn the keyswitch to the ON position.

5. Measure the voltage between terminal B of the keyswitch and engine ground.

6. Measure the voltage between terminal R of the keyswitch and engine ground.

7. Turn the keyswitch to the OFF position.

8. Turn OFF the power to the ECM.

9. Reconnect all wires to the original configuration.

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 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

Test Step 5. Check the Voltage from the Main Relay to the Fuse for the Engine Control

1. Turn OFF the power to the ECM.

2. Remove the wire 112-PU(Purple) from the normally open terminal of the main relay.

3. Turn ON the power to the ECM.

4. Turn the keyswitch to the ON position.

5. Measure the voltage between the normally open terminal of the main relay and engine ground.

6. Turn the keyswitch to the OFF position.

7. Turn OFF the power to the ECM.

8. 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. Proceed to Test Step 6.

Test Step 6. Check the Voltage at the Main Relay

1. Turn OFF the power to the ECM.

2. Remove the wire 308-YL(Yellow) from the coil of the main relay.

3. Remove the wire 101-RD(Red) from the normally open contact of the main relay.

4. Turn ON the power to the ECM.

5. Turn the keyswitch to the ON position.

6. Measure the voltage between wire 308-YL(Yellow) and engine ground.

7. Measure the voltage between wire 101-RD(Red) and engine ground.

8. Turn OFF the power to the ECM.

9. 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(Black) has continuity to engine ground. If wire 200-BK(Black) 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(Red).

  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(Yellow).

  Repair: Repair the wire between the main relay and terminal R of the keyswitch.

  STOP