Where engine hours come from, and why they might not match the dashboard

Engine hours always come from the vehicle's own onboard computer (the ECM). They are not calculated by timing how long the ignition wire has been live.

This makes the install type decisive:

• If the device reads ECM data, through the correct wiring harness or via a camera with vehicle-scan capability, it receives accurate engine hours from the vehicle itself.
• If the device does not have the correct harness to read the ECM, it does not receive engine hours at all. They cannot be estimated or substituted from ignition on/off timing; there is no fallback calculation.

If engine hours do not match the dashboard

A mismatch, commonly in the range of one to ten percent, is almost always a wiring question rather than a platform calculation error. Check first that the correct harness is installed and wired correctly. Geotab publishes a harness reference you can check a vehicle against: harness cheat sheet.

When the harness is correct, engine hours should match the vehicle's dashboard one to one. A mismatch that persists after the wiring has been confirmed points to an installation issue.