Applies to: BMU5
What does Scania BMU fault code 646 mean?
The current value from the propulsion battery is outside the permitted maximum value. If the current has been above 950 A the propulsion battery main fuse has tripped. If the current has been below 950 A but above the permitted value, the propulsion battery current sensor has detected this.
What causes Scania DTC 646?
Short circuit in the electrical cable with voltage class B
How does the system react?
- Depending on the severity of the short circuit, the contactor unit or fuse will deal with it. Uncontrolled current 450-950 A is stopped by the contactor unit. Current above 950 A is stopped by the fuse. Current below 450 A is only dealt with if the maximum temperature of the propulsion battery is exceeded. After a short circuit, it is not possible to start the electric drive system and fault codes 631, 610 are generated. - Risk of VOR. The electric drive system stops working because the propulsion battery is not available. Direct current converter E84 (DCC) is not supplied with voltage class B and the 24 V system will drain the 24 V batteries. - Yellow warning indication of an electric drive system fault is displayed.
How to fix Scania BMU fault code 646?
- Warning!
- Renewing cable harnesses, renewing the contactor unit and troubleshooting in the propulsion battery is electrical work and must only be carried out by authorised personnel.
- Switch off and lock the interlock loop control switch.
- Turn the power off and on with the starter key.
- Read the status of the insulation fault, see RES > BMU > Monitoring signals in the RES system.
- Visually check the cable harnesses.
- Switch off the 30 voltage.
- Disconnect the central electrical unit according to WSM > 16-01 Central electric unit > P7, Central electric unit for voltage class B > Removal
- Central electrical unit.
- Measure on the propulsion battery according to WSM > 16-26 Propulsion battery and power electronics > E83, propulsion battery > Check
- Insulation troubleshooting.
- Check whether there are any fault codes for insulation.
- Follow the instructions in the Workshop Manual Troubleshooting a short-circuit in the voltage class B circuit.
- Renew the contactor unit in the propulsion battery according to WSM > 16-26 Propulsion battery and power electronics > E83, propulsion battery > Renewal
- Contactor unit.
- If the main fuse for propulsion battery E83 has been triggered, life the propulsion battery out according to WSM > 16-26 Propulsion battery and power electronics > E83, propulsion battery > Removal – propulsion battery.
- When renewing the contactor unit, carry out a Calibration of propulsion battery information.
- Renew the main fuse in the maintenance disconnector in the propulsion battery WSM > 16-26 Propulsion battery and power electronics > E83, propulsion battery > Renewal
- Main fuse.
This information is for guidance only. Always follow the manufacturer workshop manual and safety procedures; if in doubt, contact an authorised workshop.