Diagnostics 44 www.aftermarketonline.net OCTOBER 2026 Tracking down intermittent injector faults Intermittent faults can be some of the hardest to pin down, particularly when the evidence has a habit of disappearing during testing. DiagnoseDan takes a closer look at one such problem affecting VAG diesel engines, where uneven running and injector circuit fault codes can be traced to a fault within the injector itself. A Volkswagen Audi Group (VAG) vehicle fitted with an EA288 evo or EA897 Gen 3 engine comes into the workshop with the malfunction indicator lamp (MIL) on and the engine running unevenly at idle. The injector fault may be intermittent, with one or more of the following codes stored: P020100 – Injector Circuit, P020200 – Injector Circuit, P020300 – Injector Circuit, or P020400 – Injector Circuit. There may be some other clues too, including failed diesel particulate filter (DPF) regeneration or an extended cranking time when the engine is first started. One possible cause is an intermittent internal electrical failure within an injector, specifically involving the piezoelectric sensor built into the threepin solenoid injector. What’s happening inside the injector? The Bosch three-pin solenoid injectors used in these engines feature integrated Needle Closing Control (NCC). Each injector has a piezo sensor positioned directly above the solenoid valve’s anchor pin. During the injection cycle, changes in fuel pressure within the valve control chamber create a mechanical force that is passed through the anchor pin to the piezo sensor. The sensor converts this into a proportional electrical voltage signal and sends it back to the engine control unit (ECU) through Pin 2 of the injector connector. This feedback allows the ECU to identify three important stages of the injection event. Needle opening is identified by a specific drop in pressure within the valve control chamber and a corresponding change in voltage from the piezo sensor. The needle return point is at the peak of the injector needle stroke, where sensor voltage increases as the valve armature closes. Finally, another increase in sensor voltage tells the ECU when the nozzle needle is fully seated, and the needle has closed. The pressures involved are considerable. Maximum injection pressure is 2,200 bar on the 2.0-litre EA288 evo TDI and 2,500 bar on the 3.0-litre V6 EA897 Gen 3 TDI. So, what happens when it goes wrong? The piezo sensor provides feedback from the needle closing event, which the ECU uses to regulate injection timing and quantity adjustment. If the internal sensor fails, the ECU
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