Possible reasons and how to eliminate them:

• If engine hours are detected by ignition sensor, the reason can be that data coming from this sensor is incorrect. Check sensor properties: parameter, calculation table, validation, etc.
  

• For accurate engine hours calculation the equipment should send a valid parameter value of an engine sensor. In case of receiving an invalid value it is necessary to replace sensor with validator using the correct value (for example, 0).
  

• The value of 'Maximum interval between messages' (adjusted on the Advanced tab of unit properties) is less than a typical interval between messages transmission. That is why intervals of engine hours are wrong. In this case, set the parameter 'Maximum interval between messages' as zero or give it another adequate value.