Scania EMD DTC 257 Intake air mass flow sensor T126

EMD EMD control unit · Scania

Code 257 (decimal). Some diagnostic tools show it in hexadecimal as 0101.

In short

Incorrect measurement value for intake air flow.

Applies to: EMD0EMD1

What does Scania EMD fault code 257 mean?

Incorrect measurement value for intake air flow.

What causes Scania DTC 257?

- Fault in the intake air mass flow sensor. - Leaks in the EGR circuit. - Leaks in the charge air system. - Fault in another sensor in the gas exchange system: exhaust gas pressure sensor T125, charge air pressure sensor T122 and charge air temperature sensor T121.

How does the system react?

The engine control unit switches off the EGR circuit. The engine power is reduced. Only for vehicles with Euro 5: The fault code cannot be cleared when it is active.

How to fix Scania EMD fault code 257?

  1. If there are additional fault codes for mass flow sensor T126, rectify these first.
  2. Check Mass flow sensor.
  3. Check Exhaust gas pressure sensor.
  4. Check Charge air pressure sensor.
  5. Check Charge air temperature sensor.
  6. Check for leaks in the EGR circuit or charge air system.
  7. Note: Always carry out a default setting of the mass flow sensor adaptation values if the mass flow sensor has been renewed, or if leakage in the engine intake system has been rectified.
  8. Applies only to vehicles with Euro 5: If the operating time since the fault code was generated exceeds 10 hours, drain the EGR cooler as there is a risk that condensed water will form in the air-cooled EGR cooler when the EGR system has been switched off.
  9. Drain the EGR cooler according to the instructions in the Workshop Manual, subgroup 01-65.

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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