Fault code: 275 SCANIA

Error identification:

The voltage in the circuit has been above the permitted level.

Cause:

Possible causes:

• Open circuit in charge air temperature sensor circuit.

• Fault in the circuit of the charge air pressure sensor, coolant temperature sensor, fuel supply pressure sensor or fan speed sensor.

Notes:

There is a common voltage supply for the coolant temperature sensor, charge air pressure sensor, charge air temperature sensor, fuel supply pressure sensor and fan speed sensor. If a fault occurs in one of the sensors, the other sensor circuits may be affected.

If the voltage is outside the permitted range, the control unit uses a pre-programmed value.

For engines with EGR, the engine runs with EGR but without any feedback from the mass flow sensor. This means that the control unit only makes a rough adjustment of EGR content using predefined values for the position of the EGR damper. Calibration of the mass flow sensor is switched off.

The fault affects the vehicle s emissions of nitrogen oxides (NOx) and the lamp which warns about a high level of contaminants comes on in the instrument cluster. A text message is also displayed in vehicles with NOx monitoring.

Vehicles with NOx monitoring

An active fault code limits the maximum engine torque by approximately 40% after the engine has been running for 50 hours.

An active fault code cannot be cleared from the control unit. When the fault has been rectified, the control unit must verify that the fault has been rectified in order for the fault code to become inactive.

Action:

Check that coolant and charge air are approximately the same temperature when the engine is cold.

Check the charge air temperature sensor, coolant temperature sensor, charge air pressure sensor, fuel supply pressure sensor and fan speed sensor, along with the harness-to-harness connectors and electrical cables in the circuits.

Proceed as follows to verify that the fault has been rectified:

Start the engine and run it at idling speed for at least 15 seconds.

If the fault is resolved, the fault code becomes inactive. Clear the fault code.

Switch the power off and on with the starter key three times in succession at 10 second intervals to turn off the warning lamp.

Error identification:

For engine control units manufactured before February 2009:

Fault in the charge air temperature sensor T121.

For engine control units manufactured after February 2009:

Fault in intake air temperature sensor T126. The sensor is constructed from the same components as the intake air flow sensor. The voltage in the circuit has been higher than normal.

Cause:

Short circuit to battery voltage.

Power failure.

Notes:

For engine control units manufactured before February 2009:

Engine power can be affected and there is a risk of black smoke.

For engine control units manufactured after February 2009:

Engine power could be affected.

Action:

Check the circuit components, harness-to-harness connectors and electrical cables.

Check that the resistance of the sensor is approximately 2.5 kohms at 20°C.