This test must be performed prior to diagnosing certain specific hybrid faults. This test verifies the quality of the standard battery system and the main power and ground supplies to the Hybrid Control Module (HCM), Transmission Electronic Control Unit (TECU), and Electronic Clutch Actuator (ECA).
Note: This test is called out in the procedures when it is required.
Electrical Pretest Detection
The power-up self-check is performed automatically each time the key is turned on. Turn the key on and watch the “Service” light. If power-up stops with the “Service” light constantly on, or it never comes on, self-check has failed.
Conditions to Set Fault Code Active
- FMI 2 is set whenever DC/DC voltage feedback signal reads greater than 15 volts or less than 10 volts and ePTO mode is engaged.
- FMI 4 is set if the voltage feedback is less than 15 volts and greater than 10 volts and the difference between the voltage feedback and the vehicle battery voltage is greater than 0.5 volts for 1 second or more.
A weak power supply can cause many issues such as shift performance, power-up or failure to crank.
Possible Causes Indicated by Eaton Fuller Hybrid Transmission Electrical Pretest
Low-voltage can be caused by the following:
- Low batteries
- Charging system
- Power harness connections or fuses to TECU, HCM or ECA