The freeze frame: half a diagnosis in one table
Along with the code the car stores the conditions it was recorded under. That is what tells a one-off from a permanent fault.
When the unit stores a fault, it takes a snapshot: engine speed, temperature, load, vehicle speed, fuel trims — everything that was true at that second. The snapshot is called a freeze frame, and it says more about the fault than the code itself.
Why it matters more than it seems
The code answers «what». The freeze frame answers «when» — and that decides where to look:
- 20 °C — the trouble showed up on a cold engine. Look at what changes during warm-up: the thermostat, the injectors, the temperature sensor.
- 90 °C, 80 % load, 110 km/h — the trouble happens under load on the motorway. Tired plugs, a weak pump, a blocked catalyst.
- 800 rpm, 0 km/h — the trouble is at idle. An air leak, a dirty throttle.
The same P0171 in the first and the second case means two different repairs.
How to read it
The app shows the freeze frame next to the code. Look at four numbers:
- Engine speed — standing or moving.
- Coolant temperature — warm or not.
- Load — coasting or pulling.
- Fuel trims — what the mixture was at that second.
What you must not do with it
Clear it without writing it down. Clearing the code takes the freeze frame with it — and the mechanic gets «there was a fault» without a single condition. That is half a diagnosis thrown away with one press.
Why it matters when buying
The freeze frame shows the conditions under which the car caught trouble before you. «A one-off, in winter during warm-up» and «every motorway trip under load» are different prices.
