Engine control module data after a crash

It is a module, not a cockpit voice recorder

A heavy-truck engine control module records a short buffer of data: speed, brake use, throttle, clutch, and engine RPM, often for a brief window around a sudden deceleration. Some trucks also have a separate crash-hardened recorder or a telematics unit that captures a longer history. There is no one "black box" and no one file format.

Federal safety rules do not set a retention period for ECM data. 49 CFR 390.15 requires an accident register and copies of accident reports the carrier is required to keep, not a download from the engine. If the truck is repaired and goes back to work, the buffer is often overwritten. If the truck is totaled, the module can leave with the salvage buyer.

Imaging has to happen early

A proper download is done with the right commercial software, a write-protected process, and a record of the chain of custody. A phone photo of a dashboard is not a download. If the truck is in a yard, a preservation letter plus a specific request to image the ECM, the telematics unit, and any dashcam is the practical move. If the truck is at a salvage pool, the letter needs to reach the insurer and the salvage yard the same week.

The evidence table lists ECM with no federal minimum and a practical risk of overwrite or loss at salvage. That is what happens when a truck is a business asset the carrier wants back on the road. It is not a timer this site invented.

Who to write

Write the operating carrier, the insurer on the federal filing, any telematics vendor you can identify from the cab or the carrier's website, and the location currently holding the truck. Use the carrier lookup to get the legal name and the process-agent path. Then use the preservation-letter template so the request is specific about ECM imaging, not only "please keep documents."