Scania BMU DTC 774 Coolant pump (M38/M82) in the propulsion battery cooling system is not behaving properly

BMU Battery Management Unit · Scania · 2 variants

Code 774 (decimal). Some diagnostic tools show it in hexadecimal as 0306.

In short

The coolant pump in the propulsion battery cooling system is not responding correctly to a request. The rotational speed of the coolant pump of the propulsion battery 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 774 mean?

The coolant pump in the propulsion battery cooling system is not responding correctly to a request. The rotational speed of the coolant pump of the propulsion battery cooling system does not correspond to the requested rotational speed.

What causes Scania DTC 774?

- 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 or reduced cooling of the propulsion battery E83.

How to fix Scania BMU fault code 774?

  1. Check that the coolant level is within specified limits.
  2. If not, fill with refrigerant and run the pump in bleeding 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 silt and sand.
  4. If the quality of the refrigerant is poor, change the refrigerant.
  5. Check the fuse of the coolant pump for the propulsion battery cooling system.
  6. Check the cable harness for the coolant pump of the propulsion battery cooling system.
  7. Check if any cables are chafed or defective.
  8. Check the harness-to-component connectors of the coolant pump for the propulsion battery cooling system.
  9. Renew the propulsion battery cooling system coolant pump M38.
  10. Renew the BMU E81.
  11. When renewing BMU, run Calibrating propulsion battery information.

Variant 2: Incorrect behaviour of the coolant pump of the propulsion battery cooling system

Applies to: BMU5

Detection

The coolant pump in the propulsion battery cooling system is not responding correctly to a request. The rotational speed of the coolant pump of the propulsion battery 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 or reduced cooling of the propulsion battery E83.

How to fix

  1. Check that the coolant level is within the acceptable interval.
  2. If not, fill with refrigerant and run the coolant pump in venting mode.
  3. Check that the refrigerant quality is acceptable: - colour. - viscosity. - clarity. - free from sludge and sand.
  4. If the refrigerant quality is poor, renew the refrigerant.
  5. Check fuse No.
  6. 1 in F564 for the coolant pump of the propulsion battery cooling system.
  7. Check the cable harness for the coolant pump of the propulsion battery cooling system.
  8. Check if any cables are chafed or defective.
  9. Check the harness-to-component connector for coolant pump M38 in the propulsion battery cooling system.
  10. Check that harness-to-component connectors M38-A, M38-B and E81-B are connected.
  11. Disconnect harness-to-component connector M38-B and measure the voltage on the electrical cable between connectors M38-B2 and M38-B3.
  12. If the voltage is < 22 V, troubleshoot the electrical cable with supply voltage on coolant pump M38 and the 24 V system.
  13. Renew coolant pump M38 in the propulsion battery cooling system
  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.

Code 774 in other Scania systems

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