I've just changed the reluctor rings and speed sensors on a 2012 L322 as rings had swolen and were stuck in the hubs.
The rear sensor is now working fine but the front sensor is still reading zero. As there.were two supplied I've changed out first one for the other new one, no difference in the Live data reading.
I've pulled the multi plug on the ABS module and continuity checked from there to the female socket behind the wheel and that is fine... which leads me on to...
If I rotate the hub should I get a fluctuating resistance reading across the speed sensor?
I'm wondering if the ebay speed sensors could be an issue and if there was a way to check them without sourcing another one?
Otherwise it's the ABS module but as the ABS system and vehicle in general was fine when it drove into the workshop I'm hoping its the speed sensor.
Any ideas would be great

Not much direct help but I gave up on EBay/ cheap sensors along time ago.
Too many were utter crap.

The speed sensor gives a pulsed voltage output. From the workshop manual:

"The wheel speed sensors are 2 wire Hall Effect type sensors. These sensors picks up on a 48 pulse incremental wheel speed sensor pole wheel on the drive shaft. 48 pulses = one complete wheel revolution. The sensor receives a stabilized 8 volt power supply to hall element on one wire, ground path for sensor through second wire back to the ABS ECU. The signal is generated by the pulse wheel affecting voltage flow through the hall element creating a low of 0.75 and a high of 2.5 volts. The sensors provide immediate vehicle speed recognition."

I suspect that trying to measure the sensor output without it connected in circuit won't be successful.