-on AC controller trucks code 42 is pump motor controller overheated
-on SX transistor controllers (the big black or gray box), code 42 is motor armature offset voltage is too high
And as brewski pointed out:
-EV100LX, ZX and ZXT controllers the code is for the control motor current sensor input missing (so check the green and yellow wires both and the connection on the card where they connect at the PZ4 plug).
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If it is a EV100 controller it is an open green sensor wire. If it is a SEPEX transistor controller it is a faulty Main controller.
Is this a SCR truck or a SEPEX truck?