Power and Grounding Considerations 4.1.4 ECU Internal Battery The ECU has an internal battery that powers critical circuits and battery backed memory when all power sources are disconnected from the ECU. The internal battery is expected to meet a 15-year battery life if the ECU is stored, or switched off without any external battery connection, at a storage temperature at or below 30° C. The exact storage life is dependent on temperature. The storage life may fall to as low as 10 years if the storage temperature is elevated to 70° C. 4.2 Engine Grounding Proper grounding for vehicle and engine electrical systems is necessary for proper performance and reliability.
Improper grounding results in unreliable electrical circuit paths. Stray electrical currents can damage main bearings, crankshaft journal surfaces, and aluminum components. They can also cause electrical noise, degrading control system, vehicle, speedometer, and radio performance. These problems are often very difficult to diagnose and repair. All ground paths must be capable of carrying any conceivable fault currents.
4.2.1 Correct Power Supply Wiring • ECU battery (+) wires connect directly to battery, not via starter motor • ECU battery (-) wires connect directly to battery, not via chassis or engine ground • Power supply wires go to all four positive pins and all four negative pins on the ECU connector • Engine is grounded and connected directly to battery ECU Connector Engine Starter Motor Battery Disconnect Switch Chassis NOTE: Circuit breakers are not shown in the figure above. A P P L I C A T I O N A N D I N S T A L L A T I O N G U I D E 21