Why is my washer pump stopping?

Having this problem on the Fisher&Paykel clothes washer. GWL11, but it's happened on the GWL15 as well.

Diagnostic code shows "Pump blocked" error code 37. But there is no blockage (i've pulled the whole machine apart and it's clear).

The washer fills fine, and starts the agitation cycle no problem. But when getting to the next (rinse) cycle, the pump will only run for 10-15 seconds and then cuts out. If I restart the machine, and forward to "rinse" it will again run for 10-15 seconds and cut out.

Same thing when I put it in diagnostic mode - I can turn on the pump for 10-15 seconds but then it stops. If I wait 5-10 minutes it will turn on again.

Is there some kind of sensor that would cause the pump to stop working? Would the motor/pump controller cut it off for some reason?

I've measured the impedance on the pump. Spec is 7 ohms and mine reads 5.3 ohms. I've swapped out the pump for another used pump and get the same problem and the same reading.

Problem seems to be either the pump or the motor controller, but I can't tell which! If I buy both I'm spending around $300...may as well buy a new machine!