Diagnostics basics
What is live data and what is it for?
Live data are the readings the control unit uses at each moment, such as rpm, engine temperature, incoming air or the mixture correction, and they can be viewed through the OBD port. They help check whether a sensor says something sensible and find faults that have not left a code yet.
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Which data can you see?
Emissions diagnostics offer a standardized list: rpm, speed, calculated load, coolant and intake air temperature, airflow or manifold pressure, throttle position, fuel trims, oxygen sensor voltage and distance since codes were cleared, among others.
Each car publishes only part of that list. Data from other control units (transmission, ABS, battery) and much of the engine's can only be read with the manufacturer's protocols.
How do you read them?
The useful thing is to compare: a temperature sensor showing the same as the outside air with a hot engine, or a very high mixture correction, point to a specific cause.
For many values there is no universal figure: the right value depends on the engine. The manufacturer's service information and a comparison with an identical car that runs well are the reference.
Why record them?
Many faults only show up on the move: a stumble when accelerating, a boost drop or a sensor that fails when hot. Recording data during a road test lets you look at it calmly afterward.
General guidance only: every manufacturer and model has its own details. Always follow your vehicle's manual and, if in doubt, ask a workshop.
Related
Related trouble codes
- P0101Mass or volume air flow sensor A, circuit: range/performance
- P0128Coolant thermostat: coolant temperature below the thermostat regulating temperature
- P0171Mixture too lean (bank 1)
Related symptoms
- Car uses more fuel than normal: causes and what to check
- Car jerks when accelerating: causes and what to do
Learn more
See what your car is saying
With the ECO-LITE, your workshop can view live data and record a log during a road test, without riding in the car.
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Frequently asked questions
What is the difference between live data and freeze frame?
Live data is what is happening now; the freeze frame is a snapshot of that data at the moment a fault was stored.
Can I see boost pressure or the particulate filter's soot load?
It depends on the car: some publish it through standardized diagnostics and others only with the manufacturer's protocol.
Does live data drain the battery?
With the engine running, not noticeably. With the engine off and the ignition on, it does use the battery, like any load.