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Check Engine Light Question

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Depends on the DTC. Some have to exceed certain thresholds over a set number of cycles. Some require errors to pop up through multiple drive cycles - some are more quicker acting. Also depends on the monitor that is looking at target sensors - some are continuously monitored, some are not.


Without getting into too much detail - most DTCs that people will run into will be 1-trip DTCs or 2 -trip DTCs.


- 1-trip DTCs include things like misfires and fuel system failures, things that could cause extensive damage to the powertrain if not remedied quickly.


- 2-trip DTCs will not illuminate the CEL until a failure condition is met a second time. Some require two detections in consecutive drive cycles, some do not. These include EVAP, emissions, etc.


To get more information - you'll have to look at the FSM for your specific model for the error conditions, the low level conditions that set the DTC or not. Very rarely will someone have to diagnose it down to that level, unless there is something fundamentally wrong with the monitoring system. Most recent case that I could think of was the SUA complaints on certain Toyota models with DBW. There, they had to run it down to the firmware on the ECM to see if this was something that was properly monitored or not.

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Depends if it is modal or transient. Again, it is detemined by what DTC is set. Some are long duration - ie, # of start stops, average speed, time on/time off, etc. Some are very short in duration - sometimes as short as the resolution of the sensor itself - like the knock sensor.


Can by tied to physically driving the car, some are queried as the car is first started.

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