Hi we have this Yale erp25alf E216A02706G

The original fault was jerky drive but everything else working and no error codes.
We initially replaced the speed encoder. Made no difference, so ordered another encoder from yale. Still made no difference. The wiring from the encoder to the inverter are all intact.

We then had the motor sent away for test. Which came back saying no fault on the motor.

At this point we replaced the AC traction inverter. Still the same fault. If the truck was tested off the floor it would drive ok but under load would judder and wheels turn slowly.
We had plugged in and tested with the etacc software and foot pedal was working ok.
After leaving it a few days the fault changed to the truck will drive for a bit then throw up error 66.

Now we have checked for shorts on the cables and earth leakage. All clear. We have run out of tests we can do now and was really hoping someone might be able to point us in the right direction or have come across a similar problem.

Thanks in advance.