Honda 2008 Ridgeline Owner's Manual page 322

Emissions Testing
8. Then drive in city/suburban
traffic for at least 10 minutes.
When traffic conditions allow, let
the vehicle coast for several
seconds without using the
accelerator pedal or the brake
pedal.
9. Make sure the vehicle has been
parked with the engine off for 30
minutes.
If the testing facility determines the
readiness codes are still not set, see
your dealer.
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