SPRING 0966808 - Caterpillar

Use this procedure to troubleshoot the electrical system if a problem is suspected with the power to the Electronic Control Module (ECM). Also, use this procedure if one of the diagnostic codes in Table 1 is active or easily repeated.
Table 1
Diagnostic Codes
CDL Code Code Description Comments
168-2 Electrical System Voltage : Erratic, Intermittent, or Incorrect The engine is running. The battery voltage falls below 6 VDC and the voltage returns above 9 VDC for three voltage readings in the last 7 seconds.
168-3 Electrical System Voltage : Voltage Above Normal The ECM detects voltage that is above the acceptable value.
168-4 Electrical System Voltage : Voltage Below Normal The ECM detects voltage that is below the acceptable value.
1834-2 Ignition Key Switch loss of signal The ECM detects an erratic signal from the keyswitch. The keyswitch is cycled at least three times in the last second.
3467-5 Main Power Relay:Current Below Normal The ECM detects a low current in the circuit that is for the main power relay for the machine.
The ECM can only detect this condition when the output driver is not activated.
3467-6 Main Power Relay:Current Above Normal The ECM detects a low current in the circuit that is for the main power relay for the machine.
The ECM can only detect this condition when the output driver is activated. The engine ECM requires the keyswitch to be in the ON position in order to maintain communications with Caterpillar Electronic Technician (ET).
Illustration 1 g02060084
Schematic for the electrical power supply circuit
Test Step 1. Check for Active Diagnostic Codes
Establish communication between Cat ET and the ECM . Refer to Troubleshooting, "Electronic Service Tools", if necessary.
Start the engine. Run the engine until the engine is at normal operating temperature.
Observe the "Active Diagnostic" screen on Cat ET. Wait at least 30 seconds so that any codes may become active. Look for these codes:
168-2
168-3
168-4Results:
Active 168-2 or 1834-2 - Proceed to Test Step 2.
Active 168-3 - Proceed to Test Step 3.
Active 168-4 - Proceed to Test Step 4.Test Step 2. Inspect the Electrical Connectors and the Wiring for the Charging Circuit
Turn the keyswitch to the OFF position.
Check the harness connections at the battery and at the alternator.
Check the harness between the battery and the alternator. Results:
OK - The harness and connectors appear to be OK.Repair: There is a problem with the charging system. Refer to Special Instruction, REHS0354, "Charging System Troubleshooting".STOP
Not OK - The connectors and/or wiring are not OK.Repair: Repair the wiring and/or the connectors. Replace parts, if necessary. Ensure that all of the seals are properly in place and ensure that the connectors are coupled. Verify that the repair eliminates the problem.STOPTest Step 3. Check the Charging Circuit
There is a problem with the charging circuit. Results:
Not OK - The battery voltage is high.Repair: There is a problem with the charging system. Refer to Special Instruction, REHS0354, "Charging System Troubleshooting".STOPTest Step 4. Check the Battery
Turn the keyswitch to the ON position. Do not start the