Mass flow sensor
Error identification: The voltage in the circuit has been below the permitted level.
Cause: Possible causes are:
• Short circuit in mass flow sensor circuit.
• Fault in the fuel temperature sensor circuit or oil pressure sensor circuit
Notes: There is a common voltage supply for the mass flow sensor, oil pressure sensor and fuel temperature sensor. If a fault occurs in one of the sensors, the other sensor circuits may be affected.
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 the mass flow sensor, oil pressure sensor and fuel temperature 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:
There must not be any active fault codes for the voltage supply to sensors or for battery voltage.
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.
Intake air mass flow sensor T126
Error identification: The voltage in the circuit has been below the permitted level.
Cause: The fault can be due to any of the following:
• Short circuit to ground.
• Power failure.
Notes: The engine control unit switches off the EGR circuit.
The engine power is reduced.
Applies only to vehicles with Euro 5:
The fault code cannot be deleted when it is active.
Action: Check the mass flow sensor and its harness-to-component connectors and cable harness.
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.
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 circuit has been switched off. Drain according to the instructions in Workshop Manual, sub-group 01-65.