40021 3 Mercruiser NUT

Table 1
Diagnostic Codes Table    
Code and Description    Conditions which Generate this Code    System Response    
168-0 Electrical System Voltage : High     The battery supply voltage is greater than 32 VDC for 0.5 seconds.
The engine's ECM has been powered for three seconds.
The engine is not being cranked.     The code is logged.    
168-1 Electrical System Voltage : Low     The battery supply voltage is less than 18 VDC for 0.5 seconds.
The engine's ECM has been powered for three seconds.
The engine is not being cranked.    
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 seven seconds.    Unswitched battery voltage is supplied to the ECM at P1-48, P1-52, and P1-53. The ground 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 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 circuit breaker for the engine ECM.The engine ECM requires the keyswitch to be in the ON position in order to maintain communications with Caterpillar Electronic Technician (ET).
Illustration 1 g01685214
Schematic for the electrical power supply circuitTest Step 1. Inspect the Electrical Connectors and the Wiring
Turn the keyswitch to the OFF position.
Illustration 2 g01415758
Location of ECM connectors
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.
Illustration 3 g01416914
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
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 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.STOPTest Step 2. Check the Battery Voltage at the ECM
Turn the main breaker to the OFF position.
Disconnect the J1/P1 ECM connector.
Turn the main breaker to the ON position.
Turn the keyswitch to the ON position.
Wiggle the wires in the harness while performing the following test steps.
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).
Turn the main breaker to the OFF position.
Reconnect the J1/P1 ECM connector.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. Check the wiring between the ECM and the batteries. Proceed to Test Step 4.
Keyswitch voltage out of range - The voltage is not correct for the keyswitch circuit at the ECM. Proceed to Test Step 3.Test Step 3. Check for Voltage at the Main Relay Contact
Remove wire "PU-06" from the contacts of the main relay.
Turn the main breaker to the ON position.
Turn the keyswitch to the ON position.
Measure the voltage between the wire "WH-06" terminal on the main relay and engine ground.
Measure the voltage between the wire "PU-06" terminal on the main relay and engine ground.
Turn the keyswitch to the OFF position.
Turn the main breaker to the OFF position.
Reconnect wire "PU-06" to the contacts of the main relay.Expected Result:The measured voltage is between 22 VDC and 27 VDC.Results:
OK - The measured voltage is between 22 VDC and 27 VDC. Repair: Repair the wire between the main relay and the ECM.STOP
Not OK - The measured voltage is not between 22 VDC and 27 VDC on the wire "PU-06" terminal and the voltage is between 22 VDC and 27 VDC on wire "WH-06" terminal. Proceed to Test Step 5.
Not OK - The measured voltage is not between 22 VDC and 27 VDC on wire "WH-06" terminal. Repair: Check the wiring between the main relay and the batteries. Proceed to Test Step 4.Test Step 4. 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 "CB 4" or the main breaker are 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 between the battery and the ECM connector J1/P1.STOP
Not OK - The battery voltage