If the starter does not turn, then the first thing to check is whether, when the engine is started, the voltage necessary for its operation, the value of which is at least 10 V, is supplied to terminal 50 of the traction relay. If the voltage is less than the specified value, then you need to check the starter circuit wires according to the diagram. Starter motor operation at full voltage can be checked as follows.
When the gear in the gearbox is not engaged, turn on the ignition.
With wire (section not less than 4 mm2) bridge starter terminals 30 and 50.
If the starter works normally, then the problem is in the wires going to the starter. In this case, check the starter in the removed state.
Test conditions: wire connections must be tight and not oxidized.