Piezo injector current (using a low-current clamp)

The purpose of this test is to check the current for a Piezo Diesel injector under different operating conditions.

How to perform the test

  1. It may be necessary to carefully strip back the loom outer insulation to access the injector cables. Repair the loom insulation once the tests are completed.
  2. Plug the low amp current clamp into PicoScope Channel A. Set the clamp to the 20 amp setting and zero the clamp before connecting to the vehicle.
  3. Start the engine and allow it to idle.
  4. Minimise the help screen and with the Example Waveform on your screen PicoScope has already selected suitable scales for you to capture your waveform. Select GO or press the spacebar to see live data.

Note: This waveform has been set up in Auto trigger mode, with a rising-edge trigger. If the waveform does not start with a positive pulse, the current clamp has been connected the wrong way round. Remove it and replace facing the opposite direction.

Waveform notes

These example waveforms show the injector current during different operating conditions. The positive signals are the injector open commands and the negative signals are the injector close commands.

Example 1: The first two injector phases are pre-injection and the third is the main injector phase.

Example 2: As the engine speed is raised the control module increases the duration of the main injector phase.

Example 3: On over-run only the first pilot injection phase remains.

Bosch Piezo Injector

Figure 2

Piezo injector element in 2 states

Figure 3

Technical information

Figure 2 shows a Bosch piezo injector as used in most Bosch systems since 2007. Similar injectors are made by Siemens.

Piezo injectors have the advantage over conventional electromagnetic injectors of a very quick reaction time up to four times faster.

Piezo injectors operate using of a stack of about 300 thin piezo ceramic plates. When the switching voltage is applied the plates expand opening the needle and allowing pressurised fuel into the cylinder.

As with all common-rail systems, there may be various injection phases.

  • Pre-injection or pilot phases are to combat diesel knock by gently starting combustion.
  • Main injection phase is for the power and torque characteristics.
  • Post-injection is to increase combustion temperature during diesel particulate regeneration.

Figure 3 shows a piezo element in its two different states. Illustration 1 shows the stack with no supply voltage and illustration 2 shows the increase in height of the stack when the supply voltage is switched on.

Note; Once the stack is in the injector open position it does not need to have a continuous supply voltage and will remain in the open state until the close command. For this reason never disconnect the injector multi-plug with the engine running. If the injector is in the open state it could hydraulic lock the engine with diesel fuel.

The engine will cut out if the control module detects any faults with the injectors or driver circuit.


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.

Suitable accessories

  • 30 A (low amps) current clamp


  • 20 A / 60 A DC (low amps) current clamp


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1 comment | Add comment

March 07 2017

2007 Astra diesel won’t start after turning off the engine
Then engine just start by tow another vehicle and I’d not how to check injectors power and the fuel is ok from pump.

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Guided test: Piezo (current)