Two Trip Detection Logic

DESCRIPTION
When the Powertrain Control Module (PCM) detects a malfunction during the 1st trip, the Diagnostic Trouble Code (DTC) and corresponding freeze frame data are stored in the PCM's memory. The Malfunction Indicator Lamp (MIL) will not be illuminated until the fault is detected again during the 2nd trip. Certain DTCs are capable of turning the MIL light on or blinking it during the first trip.

DTCs capable of illuminating the MIL when detected on the 1st trip:
- Misfire diagnostic trouble codes
- Catalyst diagnostic trouble codes
- Closed loop control diagnostic trouble codes

NOTE: A trip is defined as a Key-ON, Key-OFF event in which the PCM detects the following:
1. Engine coolant temperature should exceed 70°C (158°F).
2. Engine coolant temperature should change more than 20°C (68°F) after starting the engine.
3. Engine speed should go over 400 RPM.

MALFUNCTION INDICATOR LAMP (MIL)
When the PCM detects an emission related DTC during the 1st trip, the DTC and engine data are stored in the freeze frame memory. The MIL light is illuminated only when the PCM detects the same emission related DTC after it occurs in two consecutive trips. Once the MIL is illuminated, it will only turn off after the PCM detects three trips without any malfunctions occuring. DTCs that would cause vehicle emissions to exceed the federal limit are capable of illuminating or blinking the MIL during the 1st trip.