Scania BMU DTC 777 Incorrect behaviour of the coolant pump in the direct current converter E84 (DCC) and inverter E82 (MGU) cooling system

BMU Battery Management Unit · Scania · 2 variants

Code 777 (decimal). Some diagnostic tools show it in hexadecimal as 0309.

In short

The coolant pump of the direct current converter and inverter cooling system does not respond correctly to a request. The rotational speed of the coolant pump for the direct current converter and inverter cooling system does not correspond to the requested rotational speed.

Variant 1

Applies to: BMU6 (RES)BMU6 (RESXA)BMU6 (RESXB)BMU6 (RESXC)BMU6 (RESXD)BMU6 (RESXE)BMU6 (RESXF)BMU6 (RESXG)BMU6 (RESXH)BMU6 (RESXI)BMU6 (RESXJ)BMU6 (RESXK)

What does Scania BMU fault code 777 mean?

The coolant pump of the direct current converter and inverter cooling system does not respond correctly to a request. The rotational speed of the coolant pump for the direct current converter and inverter cooling system does not correspond to the requested rotational speed.

What causes Scania DTC 777?

- Poor connection. - Internal faults. - The coolant pump impeller is stuck.

How does the system react?

Yellow warning indication of an electric drive system fault is displayed.

What are the symptoms?

No cooling or reduced cooling of the direct current converter and inverter.

How to fix Scania BMU fault code 777?

  1. Check that the coolant level is within the specified interval.
  2. If not, fill with refrigerant and run the coolant pump in venting mode using Testing the solenoid valve and heater in the propulsion battery cooling system.
  3. Check that the refrigerant quality is acceptable: - colour, - viscosity, - clarity, - free from sludge and sand.
  4. If the refrigerant quality is poor, change the refrigerant.
  5. Check the fuse of the coolant pump for the direct current converter and inverter cooling system.
  6. Check the cable harness of the coolant pump for the direct current converter and inverter cooling system.
  7. Check if any cables are chafed or defective.
  8. Check the harness-to-component connector for the coolant pump.
  9. Check the voltage supply to the coolant pump.
  10. Renew the coolant pump for the direct current converter and inverter cooling system.
  11. Renew BMU E81.
  12. During BMU renewal, run Calibrating propulsion battery information.

Variant 2

Applies to: BMU5

Detection

The coolant pump of the direct current converter and inverter cooling system does not respond correctly to a request. The rotational speed of the coolant pump for the direct current converter and inverter cooling system does not correspond to the requested rotational speed.

Possible cause

- Poor connection. - Internal faults. - The coolant pump impeller is stuck.

System reaction

Yellow warning indication of an electric drive system fault is displayed.

Symptoms

No cooling or reduced cooling of the direct current converter and inverter.

How to fix

  1. Check that the coolant level is within the specified interval.
  2. If not, fill with refrigerant and run the coolant pump in venting mode.
  3. Check that the refrigerant is of an acceptable quality (colour, viscosity, clarity, free from sludge and sand).
  4. If the refrigerant quality is poor, renew the refrigerant.
  5. Check fuse No.
  6. 2 in F564 of the coolant pump for the direct current converter and inverter cooling systems.
  7. Check the cable harness of the coolant pump for the direct current converter and inverter cooling system.
  8. Check if any cables are chafed or defective.
  9. Check the harness-to-component connector for coolant pump M41 for the direct current converter and inverter cooling system.
  10. Check that M41-A, M41-B and E81-B are connected.
  11. Disconnect M41-B and measure the voltage on the electrical cable between M41-B2 and M41-B3.
  12. If the voltage is < 22 V, troubleshoot the electrical cable with supply voltage on coolant pump M41 and the 24 V system.
  13. Renew coolant pump M41 for the direct current converter and inverter cooling systems.
  14. Renew BMU E81.
  15. During BMU renewal, carry out a Calibration of information for the propulsion battery.

This information is for guidance only. Always follow the manufacturer workshop manual and safety procedures; if in doubt, contact an authorised workshop.

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