Most of the time, using a newer control module with an older mainframe that was built before January 1999 causes this. The older frames do not have the anti-arc clip installed in them. All new frames have the clip installed in them from the factory. The newer controls require the anti-arc clip (pin 3) installed in the mainframe. If the clip is missing, the controller will display a shorted input (Shi or Sho) diagnostic code. Other things cause this diagnostic to occur. They are discussed below.
This diagnostic code means that the controller is checking for a 3-degree temperature rise in 60 seconds (fast load mode). If the controller does not see this rate of change, the controller will turn off the output power for that zone and alert the user with the diagnostic code. Also check for bare, pinched or twisted wires, or excessive distance between heater and thermocouple. Also check for insufficient wattage and/or voltage applied to heater. On the DSS unit, try changing the load type to slow load mode, (controller checks for 3-degree rise in 240 seconds), see below for instructions. This is usually caused by large loads, such as manifolds having too small of a heater, or too little voltage. Also check for damage to the electronic circuitry due to excessive input voltage caused by shorted heaters. Check for shorted heater in the mold.