21908 Mercury NUT, MOUNTING BRACKET SCREW

Table 1
Diagnostic Codes Table    
Code and Description    Conditions which Generate this Code    System Response    
168-0 Electrical System Voltage high - most severe (3)     The battery supply voltage is greater than 32 VDC for two seconds.
The engine's ECM has been powered for two seconds.
The engine is not being cranked.     The code is logged.    
168-1 Electrical System Voltage low - most severe (3)     The battery supply voltage is less than 9 VDC for two 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 momentarily drops below 9 VDC or the voltage drops below 9 VDC for three voltage readings in the last seven seconds.    Unswitched battery voltage is supplied to the ECM at terminal P1-4. Engine ground is connected to the ECM terminal P1-5. The ECM receives the input from the keyswitch at terminal P1-6 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 devices for circuit protection.The engine ECM requires the keyswitch to be in the ON position in order to maintain communications with Caterpillar Electronic Technician (ET).
Illustration 1 g01408232
Typical schematic for the R1600G electrical power supply
Illustration 2 g01410947
Typical schematic for the R1700G electrical power supplyTest Step 1. Inspect the Electrical Connectors and the Wiring
Remove electrical power from the engine ECM.
Illustration 3 g01139425
ECM (1) J1/P1 connectors (2) J2/P2 connectors
Thoroughly inspect ECM connector J1/P1 and all other connectors in the electrical circuit. Refer to the electrical schematic for the complete electrical diagram of the circuit. Refer to Troubleshooting, "Electrical Connectors - Inspect" for information on inspecting electrical connections.
Illustration 4 g01408456
P1 terminals (P1-4) Unswitched +Battery (P1-5) Engine ground (P1-6) Switched +Battery
Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector.
Check the allen head screw on each of the ECM connectors for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.
Check the harness and wiring for abrasions and for pinch points from the batteries to the ECM.Expected Result:All connectors, pins, and sockets are completely coupled and/or inserted. The harness and wiring are free of corrosion, of abrasion, and of pinch points.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 circuit. Ensure that all of the seals are properly in place and 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.
Restore electrical power to the ECM.
Turn the keyswitch to the ON position.
Measure the voltage between terminal P1-4 (unswitched +Battery) and terminal P1-5 (Engine ground).
Measure the voltage between terminal P1-6 (Switched +Battery) and terminal P1-5 (Engine ground).Expected Result:The measured voltage is between 22 VDC and 27 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 - Unswitched power out of range - The voltage is not correct at the ECM. Proceed to Test Step 3.
Not OK - Switched power out of range - 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 are OK.Repair: There is an open circuit or excessive resistance in the wiring or connections between the batteries and the ECM. Verify that the following devices are not tripped.
"500A Fuse"
"80A Main circuit breaker"
"15A CB-11 circuit breaker"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.STOPTest Step 4. Check the Voltage at the Normally Open Contacts of the Main Relay
Turn the keyswitch to the OFF position.
Disconnect the wire from the main relay to "CB-5".
Turn the keyswitch to the ON position.
Measure the voltage between either side of the normally open contacts on the main relay and engine ground.
Measure the voltage between wire EL308-YL on the coil of the main relay and engine ground.
Turn the keyswitch to the OFF position.
Return all wires to the original configuration.Expected Result:The voltage measures 24 3 VDC for all measurements.Results:
OK - The voltage measures 24 3 VDC for all measurements. Proceed to Test Step 6.
Not OK - Voltage is not present on the terminal from the main relay to "CB-5".Repair: If the other voltage measurements are correct, verify that wire 200-BK on the coil of the main relay has continuity to engine ground. If wire 200-BK has continuity to engine ground, replace the main relay.STOP
Not OK - Voltage is not present on the terminal of the main relay to the main circuit breaker.Repair: Verify that voltage is pr