Power and Grounding Considerations 4 Power and Grounding Considerations 4.1 Power Requirements 4.1.1 System Voltage The electronic control system can operate with either a 12 VDC or 24 VDC electrical system. The switched positive battery and the un-switched positive battery connections to the ECU are made at the P1/J1 customer harness connector. The minimum battery voltage for the ECU to actuate the fuel injectors, regardless of system voltage (12 VDC or 24 VDC) is 9 VDC. The ECU monitors system voltage input (un-switched power) and triggers a diagnostic code if the voltage drops below 9 VDC and then returns above 9 VDC.
The batteries, charging system, starter, and associated wiring must be sized and designed correctly to allow the starter to crank the engine to an appropriate minimum engine speed to start the engine. The engine installation should meet the minimum cranking speeds at the COLDEST ANTICIPATED TEMPERATURES. For C7 ACERT and C9 ACERT the typical minimum cranking speed required to start the engine is 150 rpm. For all other engines, the typical minimum cranking speed required to start the engine is 100 rpm. Also reference TMI System Data for Minimum Cranking Speed Data. 4.1.2 Battery (+) Connection The ECU requires four un-switched battery (+) inputs and an ignition key switch input.
When the key switch is in the off position, the ECU is in sleep mode where it draws a very small residual current through the four un-switched battery inputs. When the key switch input is turned on, the ECU will become active, allowing the engine to start and run. The ignition key switch input (switched power) is made through pin P1/J1-70 and carries approximately 2 mA on a 12 VDC system and 4 mA on a 24 VDC system. NOTE: The ECU will begin to function when the voltage at the key switch input rises above 8 VDC and ceases to function when the voltage falls below 5 VDC.
Loss of communication with ET during cranking indicates that the ECU may be shutting down due to decreasing voltage at the key switch input. It is recommended that the key switch be wired directly to battery positive through a circuit breaker. Connecting the key switch to other points in the starting system, such as the starter terminal, could cause the ECU to shut down during cranking, resulting in hard starting or failure to start. These four un-switched battery (+) input connections are made through pins P1/J1 - 48, 52, 53, and 55. These four inputs should run directly from the P1/J1 connector to the positive side of the battery.
These four inputs carry nearly all power to the ECU during peak requirements. These inputs provide the ECU power when the vehicle key switch is in the off position. Refer to Table 3 for more information on ECU current requirements. All four of these un-switched battery (+) inputs must be provided to prolong the service life of the ECU. I N D U S T R I A L E N G I N E E L E C T R O N I C S 18