SIEMENS PD PIEZO INJECTORS
SIEMENS PD PIEZO INJECTOR
These injectors are used on all 2.0 PD TDi Passat engines. (Not 1.9 PD TDi engines)
The electrical connector on a Piezo injector faces upwards and not sideways like a Solenoid injector.
Other than this, Piezo and Solenoid injectors look similar, with the injector nozzle looking like a fat nail and the pump looking like a valve spring. These injectors are always held in by two bolts.
Piezo injector failure seems mostly due to an internal electrical fault in the Piezo valve. The internal piezo wiring seems to burn out and short to the casing. The Piezo valve voltage signals are 100 -200V. Rather than risk damage to the ECU when one “shorts”, the ECU switches them all off.
The engine will cut out instantly and will not restart.
A VCDS or similar scan may give a fault code of:
17448 P1040 - Supply fuel injector(s) A, electrical malfunction in circuit
18578 P2146 - Supply Voltage for Fuel Injector Group A, Open Circuit
18579 P2147 - Supply Voltage for Fuel Injector Group A, Short to Ground
18580 P2148 - Supply Voltage for Fuel Injector Group A, Short to B+
17447 P1039 - Supply fuel injector(s) A, shorted
How to find the dud injector.
Pull the connector off an injector and start the engine. If it starts and runs on three cylinders, you have found the dud injector. Pull off, test and replace connectors until you find the dud injector.
Testing an injector.
You can’t test an injector for function but you can check the Piezo valve wiring. As this is the bit that normally fails, it is worth checking.
The piezo socket on the injector has TWO pins.
Neither should be connected to the casing (Earth or “-“).
Set your multimeter to continuity or Ohms.
Place one probe on one connector pin and the other probe on the injector body.
The meter should read “1” and not buzz.
Repeat for the other connector pin.
E.g.
If the Piezo valve has failed the meter will buzz or give a reading. A failed injector will give a reading of 400 – 500 Ohms or less.
If you are new to multimeters, an Ohm reading of “1” is not less than 400 – 500.
“1” means infinity or super super high resistance, in other words, no connection.
You must test both connector pins.
Don’t check the resistance between the two pins. It won’t tell you anything.
It is possible to remove the piezo valve part of the injector, but it isn’t easy due to the position and size of the clamp nut.
E.g.
The injector is on the left and the Piezo valve is on the right. In the centre of the piezo valve you can see a small (5mm) circle. This is the plunger that operates the injector valve to control injection.
Enlarged the piezo valve looks like this;
And like this:
From the business end it looks like this:
The schematic below shows how the piezo crystal are arranged inside the piezo valve.
The central plunger has a stack of crystals behind it. The crystals are separated by conducting plates. Each crystal receives a current from the ECU. The current from the ECU makes the crystal expand.
The expansion is so small you need a stack of crystals to move the plunger less than 0.5mm.
It is not possible to see the crystals without destroying the valve as it is sealed at the factory.
When the piezo valve fails it seems that the internal insulation breaks down and the current is conducted to the metal case.(or directly from the input to the output). When this happens the current flow is too high. The ECU immediately shuts down to protect itself from damage. The piezo crystals require a voltage between 100 – 200V which is much higher than the old solenoid valves needed. This high voltage seems to be the main reason for designing the ECU shut down.
The movement of the plunger by the crystals is so small (< 0.5mm) that it cannot trigger the injector.
Because of this, the plunger triggers the injector via a tiny lever system consisting of two tiny rockers just in front of the plunger. These will fall out of the injector when the Piezo valve is removed unless you are very careful.
At present the piezo valve cannot be replaced as Siemens don’t sell them. The only solution for a faulty injector is to replace it.
Dismantling the piezo valve.
The piezo valve cannot be dismantled without destroying it.
The following pictures were obtained after cutting one open with a hacksaw.
This is what I did;
Cut plastic connector down the middle and prised it off.
Cut connector wires to remove connector.
Pulled connector wires out of valve body.
Cut valve body top off using hacksaw.
Lifted out piezo crystal case containing piezo crystal stack.
Cut piezo crystal case top off using hacksaw.
This picture shows the parts in sequence.
The piezo crystal case.
When the crystals are energised the crystal stack increases in length forcing the plunger to move about 0.5 mm forward.
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