BMU5 Absence of TMS sub-bus CAN communication (buffer overflow)
• Check connector for TMS sub-bus on BMU(E81) pin B5 and B8. • Check wiring for TMS sub-bus: - Measure the resistance on the connector to BMU(E81) (with the 24V battery disconnected) between CAN-high (pin B5) and CAN-low (pin B8). It should be close to 60 ohm (one 120 ohm termination resistor in each end of the CAN-bus). - Measure the resistance on the connector to BMU(E81) (with the 24V battery disconnected) between CAN-high on BMU(E81) pin B5 and CAN-high on any other unit on the same CAN-bus. It should be close to zero ohm. - Measure the resistance on the connector to BMU(E81) (with the 24V battery disconnected) between CAN-low on BMU(E81) pin B8 and CAN-low on any other unit on the same CAN-bus. It should be close to zero ohm. • Check wiring and connector for the ignition signal (pin A1) on the BMU. • If no other errors can be found, change BMU(E81).
What you'll see
No driver-visible symptom recorded.
System reaction
• VOR, the hybrid system will not work since the battery will not be engaged. The DCC will not receive VCB-power and the 24-volt system will drain the 24-volt batteries. • Amber warning lamp "Hybrid System Fault" is shown in ICL
Diagnostic depth
The fault is validated as present if the ECU tries to send CAN-messages on the GMS sub-bus, but no acknowledge is received from other units, and thereby causing the internal send buffer (in the ECU) to overflow. The DTC is set to active if the buffer overflow has lasted for 50 ms. The DTC is set to inactive when the CAN-messages are sent properly again and the buffer no longer is overflowing for the last 1050 ms. The DTC is not validated (stored) if: • the ignition is turned off • first 2 seconds after ignition on • the supply voltage is below 22 volt • the supply voltage is above 32 volt
• Defect connectors on BMU(E81) for TMS sub-bus (pin B5 or B8) • Defect wiring for TMS sub-bus, open circuit on CAN-high (pin B5) or CAN-low (pin B8). • Ignition signal (pin A1) on BMU(E81) is short circuit to supply.