Skoda Octavia | Crankshaft reluctor

The fault

This vehicle was recovered from another garage after having its engine rebuilt. It would start and then cut out.

Diagnosis

There was a fault code of “engine speed sensor implausible signal”. We checked the output of the crankshaft position (CKP) sensor and found an irregularity in the waveform:

Figure 1: Several crankshaft revolutions. Upper trace: Camshaft (CPS) sensor. Lower trace: Crankshaft (CKP) sensor.

We zoomed in to get more detail:

Figure 2: Zoomed in to a single crankshaft revolution.

The crankshaft waveform (lower trace, blue) shows an obvious fault 7 to 8 teeth after TDC. Removing the crankshaft sensor and looking with a borescope, I could see that the reluctor ring had two slightly bent teeth.

Repair

I removed the sump and realigned the two bent teeth, and all was well.

Total time for diagnosis and repair: 1.5 hours