Download may experience an incident of engine misfire during certain vehicle operating conditions. The misfire may occur when the vehicle is operated between 80 – 112 KPH (50 – 70 MPH) and under light loading conditions, e.g. slight uphill road grades. This condition may occur at all ambient conditions, but is more noticeable when ambient conditions are less than 0°C (32°F). If the vehicle is equipped with On-Board Diagnostic (OBD), a MIL illumination may also have occurred due to Diagnostic Trouble Code (DTC) P0300 – Multiple Cylinder Misfire. Various single cylinder misfire DTC’s may also be present. If the frequency of misfire is high the Powertrain Control Module (PCM) may place the engine in “Limp-In” mode. The misfire condition may be caused by one or more engine exhaust valves that are slow to close. Late closure of an exhaust valve may be the result of no valve rotation and associated build up of carbon on the exhaust valve stem. This condition may occur when the engine is not allowed to run at engine RPM’s that are greater than 3,200 RPM. At 3,200 RPM or higher the engine exhaust valves will rotate if not impeded by high carbon deposits.