Reading freeze frame data
The conditions recorded at the instant a code set will often name the fault faster than the code itself — and clearing the code destroys them.
When a module stores a fault it also stores a snapshot of what the car was doing at that moment. Most technicians read the code and skip the snapshot. On an intermittent fault, the snapshot is usually the more useful of the two.
What gets stored
It varies by module, but you will typically get vehicle speed, coolant or battery temperature, state of charge, load, whether the car was charging or driving, and how long it had been running. Some modules store several frames; some store only the first occurrence, which is why clearing and re-testing can lose the best evidence you had.
Why it beats the code on an intermittent fault
A code tells you what went wrong. A freeze frame tells you when — and “when” is what you need to reproduce a fault that is not present while the car sits in front of you. A customer who says “it only does it sometimes” has just described a set of conditions they cannot articulate. The freeze frame articulates it for them.
Four questions to ask it
- Was the car moving, and how fast? A fault at zero speed is electrical or thermal. A fault at a specific speed points at something rotating, or at load.
- Cold or warm? A fault that only sets cold is a connection that closes as things expand, or a component out of tolerance until it warms.
- Charging or driving? On an EV this splits the search in half immediately — the charging path and the drive path share very little.
- High load or idle? Load pulls current, current pulls voltage down, and a marginal connection fails under current long before it fails at rest.
Reproducing the conditions
Once you have the frame, drive the conditions in it rather than driving randomly and hoping. If it set at 40 km/h with the pack at 30% and the car cold, then reproduce that — not a warm car at 80% on a short loop around the block. Most “no fault found” results are a test that never went near the conditions in the freeze frame.
When the frame contradicts the customer
It often will, and the frame is usually right. “It only happens on the motorway” against a frame recorded at 12 km/h is not the customer lying; it is them describing when they noticed it, not when it set. Trust the recorded conditions and re-interview around them.