Scania EST DTC 640 Hydraulic system

EST EST control unit · Scania

Code 640 (decimal). Some diagnostic tools show it in hexadecimal as 0280.

In short

The wheels on the controlled tag axle are not tracking properly. The system cannot keep the tag axle in a centred position when tag axle steering should be locked. The hydraulic piston is deviating by more than 5 mm from the centred position.

Applies to: EST1 (EST)

What does Scania EST fault code 640 mean?

The wheels on the controlled tag axle are not tracking properly. The system cannot keep the tag axle in a centred position when tag axle steering should be locked. The hydraulic piston is deviating by more than 5 mm from the centred position.

What causes Scania DTC 640?

- Leakage from one of the counterbalance valves. - External oil leakage from the hydraulic cylinder unit. - Internal oil leakage from the hydraulic cylinder unit.

How to fix Scania EST fault code 640?

  1. If the fault code is repeatedly activated, this indicates a fault in the hydraulic cylinder unit.
  2. Look for external oil leakage from the hydraulic cylinder unit.
  3. E.g. around the hydraulic cylinder, valves, measuring ports etc.
  4. Replace the counterbalance valves (CBV1/CBV2).
  5. If no external oil leakage has been found and the fault persists after renewing the counterbalance valves, renew the hydraulic cylinder unit (CVU).

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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