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Bosch-Common Rail System – BARO sensor


The BARO sensor is located in the PCM and measures the ambient air pressure.

With increasing geographical altitude (for example when driving up a hill) the air density and therefore the air resistance decreases. This has an effect on the engine cylinder charge and the turbocharger speed.

To avoid damage to the turbocharger and increased formation of black smoke, a BARO sensor is integrated into the PCM. It is used for making appropriate adaptations in the fuel metering and in the exhaust gas recirculation.

Effects of faults

In the event of a fault, the signal from the MAP sensor is used to determine the ambient air pressure.

If both sensors (BARO und MAP) are defective, the PCM uses a substitute value. In this case, the injected fuel quantity and therefore engine performance is significantly reduced.


The PCM continuously checks the BARO sensor for short circuits (to ground and positive) and for open control loop.

The signal from the BARO sensor is checked for plausibility by performing a comparison test with the MAP signal in a specific low load range.

Since the BARO sensor influences the EGR system, this is a MIL active component.

Possible diagnostic trouble codes: P2227, P2228, P2229.

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