Scan tool is a electronic tool used to reads what the ECU see, its the cars " live data". We use this if the car check engine light is ON this tells us what the ECU think is wrong with the car so it makes it easier for us to know where to start looking for the fault. But not all faults can be seen by the ECU there for the scan tool is limited to what it can do eg sometimes the ECU cannot read a faulty TPS so there will be no trouble code.
Example of live data problem
The car owner complains of a lack of power when cruising. The emission at idle look clean. During a road test with the scan tool recorded the following data.What is wrong?
Predicted that the fuel filter must have been plugged so the engine doesnt get enough fuel, as shown the O2 sensor reading lean, even though the injector is open for longer and the long term fuel trim i strying to richen up the fuel since the O2 is correctly shown the lean mixture. The clean emissions at idle tells us the O2 is probably works correctly , along with most of the rest of the system.
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