I tried the continuity checks as suggested by Mark, and on the OSF (which was scoping OK) we had continuity down both wires. On the NSF, the one with the missing signal we only had continuity on one wire! Ha-ha, we have found the problem....or so i thought!
Probing all other ECU pins, just as a matter of course, we found continuity on another pin! It transpires that the WDS Online wiring diagram is wrong and that the pins for the NSF sensor are 21 & 34, not 21 & 22 as shown on the diagram!! So, thanks to WDS we were on a bit of a 'red herring hunt'.
So, after scoping the correct pins and finding out wheel speed pulse, we were back to the drawing board. Whilst under the vehicle i noted that all the wheels had brand-new wheel weights hammered on. After checking the wheels & tyres i noticed that the rear tyres were extra-load types and the fronts were 'ordinary' ones. We swapped a NSR tyre with one from the OSF and the problem vanished!!! Turns out that the tyre type, even though they are all the same size & profile, makes a difference (must have been a rolling-radius difference between front & rear under acceleration)! This would explain why there were no fault codes registered - the car systems are all fine and doing what they should - it was an incorrect tyre choice by the customer that gave all the troubles with the DSC system!
So, we've learned a bit more about DSC systems and to make sure you get EVERY ounce of information out of the customer BEFORE starting investigations, the car is now back with its owner and fault-free (he's also been advised to renew the other two tyres with XL ones).
Thanks for all the advice guys - i appreciated your thoughts and guidance.
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