Freeze Frame Data

When an emission-related fault is confirmed, OBD-II requires the control unit to save key values from that moment: engine speed, load, coolant temperature, fuel trims, vehicle speed and more. This snapshot shows the conditions under which the fault happened, for example only when cold, at idle or at high load. It is often as useful as the code itself.

Typical freeze frame values include engine speed, vehicle speed, coolant temperature, engine load and fuel trims. Some control units store several frames or extended data. Freeze frame data is also a useful check after a repair. If the same fault returns, comparing the new freeze frame with the old one shows whether it happens under the same conditions, which can help separate one cause from another.

A scan tool reads the freeze frame through the diagnostic socket (OBD-II mode 02). Usually one frame is stored for the first or highest-priority fault. Usually only one freeze frame is stored for the first emission-related fault; a misfire or fuel system fault may replace an earlier, lower-priority frame.

Before clearing codes, read and note the freeze frame. Clearing erases it, and the clues needed to reproduce and confirm the repair are lost. Freeze frame data helps you understand when a fault happened: cold or hot, at idle or under load. Clearing codes also clears this data, so read and note it first.