High and Low Limits

Both the Powertrain Control Module (PCM) and the Engine Control Module (ECM) compare input signal voltages from each input device with established high and low limits for the device. If the input voltage is not within limits, and other criteria are met, the PCM/ECM will store a Diagnostic Trouble Code (DTC) in memory. Other DTC criteria might include engine RPM limits, or input voltages from other sensors or switches that must be present before verifying a DTC condition.