Bosch-Common Rail System – Combined IAT sensor and MAF sensor
1 MAF sensor
The MAF sensor measures the air mass drawn into the engine. The MAF signal has an effect on the injected quantity and the injection timing. Furthermore, the MAF signal is used to control the exhaust gas recirculation (closed control loop). There is an IAT sensor integrated into the MAF sensor.
The IAT is used to correct the MAF signal. This ensures a more precise measurement of the mass air flow. The EGR rate can be metered with greater precision. This has a positive effect on the exhaust emissions.
Furthermore, the IAT signal is used to calculate the turbocharger outlet temperature. The established value is used as a coefficient of correction when calculating the air density through the MAP sensor.
Effects of faults
If the signal from the MAF sensor fails, the EGR system is deactivated.
To calculate the mass air flow when the signal fails a substitute value is used. The substitute value for the mass air flow for each cylinder is calculated by the PCM from the engine speed.
The monitoring system checks:
• if the values output by the MAF sensor are within limits.
• the sensor for short circuit to ground/battery,
• for intermittent faults (for example loose contact),
• the sensor signals for plausibility.
Since the EGR system is deactivated in the event of a fault, this is a MIL active component.
Possible diagnostic trouble codes:
• MAF sensor: P0100, P0101, P0102, P0103.
• IAT sensor in the MAF sensor: P0110, P0112, P0113, P0071.