PIN 0969339 - 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.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 Caterpillar 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
Turn OFF the power to the ECM.
Thoroughly inspect the ECM connectors J1/P1 and J2/P2. Refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect" for details.
Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the circuit.
Check the ECM connector (allen head screw) for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
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.STOPTest Step 2. Check the Battery Voltage at the ECM
Disconnect the J1/P1 ECM connector.
Turn ON the power to the ECM.
Turn the keyswitch to the ON position.
Measure the voltage between P1-48 (Switched Positive Battery) and P1-61 (Negative Battery).
Measure the voltage between P1-52 (Switched Positive Battery) and P1-63 (Negative Battery).
Measure the voltage between P1-53 (Switched Positive Battery) and P1-65 (Negative Battery).
Measure the voltage between P1-70 (Keyswitch) and P1-63 (Negative Battery).
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