Hard Failures

A diagnostic trouble code that comes back within one cycle of the ignition key is a hard code. This means that the defect is there every time the PCM checks that circuit or function. When it is not a hard code, an intermittent test must be performed. DTCs that are for OBDII/Euro Stage III OBD monitors will not set with just the ignition key on. Comparing these to non-emission DTCs, they will seem like an intermittent. These DTCs require a set of parameters to be performed (The DRBIII® scan tool pre-test screens will help with this for MONITOR DTCs), this is called a TRIP. All OBDII/Euro Stage III OBD DTCs will be set after one or in some cases two trip failures, and the MIL will be turned on. These DTCs require three successful, no failures, TRIPS to extinguish the MIL, followed by 40 warm-up cycles to erase the DTC.

Hard failures cause Malfunction Indicator Light (MIL) to illuminate and remain on until problem is repaired. This means the defect is there every time the Powertrain Control Module (PCM) checks that circuit or function. If MIL light comes on and remains on during vehicle operation, cause of malfunction must be determined by retrieving Diagnostic Trouble Codes (DTC). See RETRIEVING DIAGNOSTIC TROUBLE CODES . If a sensor fails, PCM will use substitute value in its calculations to continue engine operation. In this condition, commonly known as limp-in mode, the vehicle runs but driveability will not be optimum.