Bosch-Common Rail System – Fuel pressure sensor

fig 1 55 Bosch Common Rail System – Fuel pressure sensor

The fuel pressure sensor measures the current fuel pressure in the fuel rail very accurately and quickly and delivers a voltage signal to the PCM in accordance with the current pressure level.

The fuel pressure sensor operates together with the fuel metering valve on the high-pressure pump in a closed-loop control circuit.

The fuel pressure sensor signal is used to:

• determine the injected fuel quantity,
• determine the start of injection,
• drive the fuel metering valve on the high-pressure pump.

Effects of faults

The fuel pressure is a critical value. If the signal should fail, it is no longer possible to carry out a controlled injection process. In the event of a short circuit or open control loop the PCM assumes a fuel pressure that is higher than the maximum permissible pressure. In response, the injected fuel quantity is set to 0 and the engine cuts out or cannot be started. The injected fuel quantity is also set to 0 if values are implausible.

Diagnosis

The fuel pressure sensor is continuously checked during analogue signal acquisition to establish whether the signal is within the limits. If the sensor voltage exceeds the upper limit, the PCM records a “limit fault high”.

If the sensor voltage in the next test cycle has fallen below the limit range again, this is registered by the PCM as “Sensor OK”. However, if the “limit fault high” message remains for a set time, this is interpreted as a fault, and the engine is ultimately stopped.

The same takes place if the lower limit range is exceeded. The sensor is also checked for short circuits (to ground and battery) and open control loop. As the engine cuts out in event of a fault, a faulty fuel pressure sensor signal has no effect on the EOBD limits. Therefore, this is a non MIL active component. In the case of a fault, the engine system fault warning lamp illuminates.

Possible diagnostic trouble codes: P0190, P0191, P0192, P0193.

08. August 2018 by sam
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