852572R02 Mercury SERVICE MANUAL

Table 1
Diagnostic Trouble Codes
J1939 Code and Description Conditions that Generate the Code System Response
158-2 Keyswitch Battery Potential : Erratic, Intermittent, or Incorrect The ECM detects an erratic signal from the keyswitch. The keyswitch is cycled at least three times in the last second. The code is logged.
168-2 Battery Potential / Power Input 1 : 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. The code is logged.
168-3 Battery Potential / Power Input 1 : Voltage Above Normal The ECM detects voltage that is above the acceptable value. The code is logged.
168-4 Battery Potential / Power Input 1 : Voltage Below Normal The ECM detects voltage that is above the acceptable value. The code is logged. The engine ECM requires the keyswitch to be in the ON position in order to maintain communications with Caterpillar Electronic Technician (ET).This procedure tests whether proper voltage is being supplied to the Electronic Control Module (ECM).The ECM is continuously powered with +Battery voltage that is supplied to inputs P1-48, P1-52, P1-53, P1-55, and P1-57 and P1-70 (keyswitch). If an emergency stop condition is initiated, the ECM relay will be energized and battery voltage will be removed from the ECM.Power to the ECM is provided by a set of normally closed contacts that are in ECM relay. The ECM relay is controlled by a set of normally open contacts in the emergency stop switch. When the emergency stop switch is placed in the STOP position, the contacts in the emergency stop switch are closed and +24 VDC is supplied to the control circuit for the ECM relay. This opens the contacts in the relay and power is removed from the ECM.Opening the battery disconnect switch will also remove power from the ECM. When the battery disconnect switch is placed in the OFF position, the ground connection to inputs P1-61, P1-63, P1-65, P1-67, and P1-69 of the ECM is removed.During an engine start sequence, the Starting Motor Magnetic Switch (SMMS) is used by the ECM to engage the starting motor. Voltage for the control solenoid for the SMMS is supplied by the ECM. When the ECM supplies the signal, the SMMS is energized. This powers the starting solenoid and the starter is engaged. Refer to the diagnostic functional test Troubleshooting, "Start Relay Circuit - Test" for information that is related to troubleshooting the circuit for the SMMS.Circuit protection is provided by circuit breakers for the ECM relay, the SMMS, and the emergency stop switch.
Illustration 1 g02511311
Schematic for the electrical power supply (typical example)
Test Step 1. Inspect the Electrical Connectors and the Wiring
Remove electrical power from the ECM.
Illustration 2 g01206567
Location of the J1/P1 and the J2/P2 ECM connectors (typical engine view)
(1) J2/P2 ECM connector
(2) J1/P1 ECM connector
Illustration 3 g01207955
Location of the engine interface connector (typical engine view)
(3) Engine interface connector
Illustration 4 g01206446
Location of the battery isolator switch, the ECM relay, and the starting motor magnetic switch (typical left side engine view)
(4) Battery disconnect switch
(5) ECM relay
(6) Starting motor magnetic switch
Thoroughly inspect connectors (1), (2), and (3). Also, thoroughly inspect the connectors for switches (4) and (6) and for relay (5). Refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect" for details.
Illustration 5 g01206553
P2 ECM connector
(P2-59) SMMS
(P2-60) Digital return
Illustration 6 g01206554
P1 ECM connector
(P1-48) +Battery
(P1-52) +Battery
(P1-53) +Battery
(P1-55) +Battery
(P1-57) +Battery
(P1-61) −Battery
(P1-63) −Battery
(P1-65) −Battery
(P1-67) −Battery
(P1-69) −Battery
(P1-70) Keyswitch
Illustration 7 g01207957
Terminal locations for the engine interface connector
(Terminal 4) +Battery
(Terminal 23) Relay control
Illustration 8 g01207940
Terminal locations for the ECM relay and the connector (typical example)
(4) ECM relay
(Terminal 1) +Battery
(Terminal 2) Relay ground
(Terminal 3) Electrical power to the ECM
(Terminal 5) Relay control
Perform a 45 N (