Products suited to this guided test*
  • Multimeter Probes

  • Back-pinning Probe Set

  • Large Dolphin/Gator Clips

  • *At Pico we are always looking to improve our products. The tools used in this guided test may have been superseded and the products above are our latest versions used to diagnose the fault documented in this case study.

CRD (Bosch) pressure regulating valve

The purpose of this test is to evaluate the operation of the Bosch Common Rail Diesel (CRD) Pressure Regulator Valve (PRV) based on the voltage and duty control under engine run conditions.

How to perform the test

View connection guidance notes.

  1. Using manufacturer's data, identify the fuel rail pressure regulator valve control signal circuit.
  2. Connect PicoScope Channel A. to the pressure regulator valve control signal circuit.
  3. Minimize the help page. You will see that PicoScope has displayed an example waveform and is preset to capture your waveform.
  4. Start the scope to see live data.
  5. Turn on the ignition and wait for the glow plug light to extinguish (if applicable).
  6. Start the engine.
  7. With your waveform on screen stop the scope.
  8. Turn off the engine.
  9. Use the Waveform Buffer, Zoom and Measurements tools to examine your waveform.

Example waveform

Waveform notes

This known good waveform has the following characteristics:

  • A switched earth, pulse width modulated (PWM) voltage, with a fixed cyclic period in which the voltage switches between battery positive at around 15 V and close to battery negative at just above 0 V.
  • The period the signal spends around 0 V, relative to the total cycle period, indicates the duty of the PWM signal. In this example, approximately one fifth of each cycle is spent close to 0 V, so the PWM duty is about 20%.
  • The signal cycles five times in a 5 ms period, indicating that it has a base frequency equal to 1000 Hz.

Waveform Library

Go to the drop-down menu bar at the lower left corner of the Waveform Library window and select Fuel pressure regulator pressure waveform.

Further guidance

Within a common rail diesel system, the Engine Control Module (ECM) uses a pressure regulator valve to control the fuel pressure within the common rail. When the ECM needs to reduce the pressure, the valve is opened and excess fuel is released to the fuel return system. Conversely, when an increased pressure is needed, the valve is closed.

The pressure regulator valve position is determined by the action of a solenoid against a spring. With these devices, the valve will move from its default position, open or closed depending on the application, when current flows through the solenoid. The greater the current, the greater the displacement of the valve. Thus, in some systems an increase in current will cause the valve to become more open, whereas in others it will cause the valve to become more closed.

The ECM can efficiently control current in a circuit using a PWM signal and, for a given electrical load, the greater the duty period, the greater the average current flowing through the circuit.

With a switched earth activated circuit the solenoid is fed with a constant battery positive on one side and, on the other side the ECM modulates the path to the earth creating current flow. Therefore, the valve is energised on, when the actuation signal is at battery negative voltage and de-energised off, when the actuation signal is at battery positive voltage. Hence the greater the duty cycle, the greater the current in the circuit and the displacement of the valve from its default position.

The ECM will vary the duty depending on the engine speed, load and temperature conditions and the torque demand from the driver, accelerator pedal position.

Refer to vehicle technical data for specific test conditions and results.

Diagnostic trouble codes

Selection of component related Diagnostic Trouble Codes (DTCs):

P0087 – Fuel rail pressure sensor or rail pressure too low

P0088 – Fuel rail pressure sensor or rail pressure too high

P0089 – Fuel rail pressure regulator performance

P0090 – Fuel rail pressure regulator control circuit

P0091 – Fuel rail pressure regulator circuit low

P0092 – Fuel rail pressure regulator circuit high

P0093 – Fuel system leak detected – large leak

P0094 – Fuel system leak detected – small leak


This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.

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Guided test: CRD (Bosch) pressure regulator valve