Eaton Fuller Hybrid Transmission Fault Code 34 – Weak Battery Voltage Fault (TECU)
Fault code for Eaton Hybrid Drive Systems models (MY08) EH-8E306A-U, EH-8E306A-UPG, EH-8E306A-UP, EH-8E306A-CD, EH-8E306A-T, EH-6E606B-CD, (MY09) EH-8E406A-U/P, EH-8E406A-UP, EH-8E406A-UPG, EH-8E406A-CD, EH-8E406A-CDG, EH-8E406A-CDR, EH-8E406A-T, EH-6E706B-CD, EH-6E706B-P and EH-6E706B-UPG. The Transmission Electronic Control Unit (TECU) is mounted to the transmission and contains the software that controls transmission operation. The Hybrid Control Module (HCM) controls the operation of the TECU during normal hybrid mode operation. The HCM main battery power is a fused 12-volt feed that runs through the HCM 38-Way Vehicle Connector with the main ground wire returning to the battery negative terminal.
Fault Code 34 – Weak Battery Voltage Fault (TECU) Detection
The following preconditions must be met before the system detects the fault:
- TECU ignition voltage is greater than 7 volts and less than 16 volts.
- TECU System Battery Voltage Low Fault is inactive.
Conditions to Set Fault Code Active
- FMI 14 is set when the TECU battery voltage drops below 9 volts for 10 seconds.
Fallback When Fault Code 34 is set the following conditions occur:
- Fault is stored in TECU memory.
- TECU switches to AutoShift Fallback mode.
- If this fault occurs while moving, it causes a 1- speed fallback.
- If the vehicle is stopped, the starting gear and reverse can be engaged.
Conditions to Set Fault Code Inactive
Only Inactive faults can be cleared from the Transmission Electronic Control Unit (TECU) or HCM history using ServiceRanger. The TECU automatically clears the faults from history after 200 hours and the HCM automatically clears the faults from history after the fault has been Inactive for 200 hours.
This fault code can be caused by any of the following:
- FMI 14
- Power supply to TECU
- Low batteries or bad main power connection
- Charging system