1. Connect the WDS or equivalent to the DLC-2.
2. Measure the PID value.
Note
PID/DATA MONITOR AND RECORD function table

Dtc p0841
TroubleshootingMazda 6 Service Manual: Contact Authorized Mazda Dealer and Have Vehicle Inspected
If any of the following warning lights or the indicator light turns on/flashes,
the system may have a malfunction. Contact an Authorized Mazda Dealer to have your
vehicle inspected.
...
Mazda 6 Service Manual: Headlights
Turn the headlight switch to turn the headlights and other exterior lights on
or off. When the lights are turned on, the lights-on indicator light in the instrument
cluster turns on.
NOTE
If the light switch is left on, the lights will automatically switch
off approximately 30 seconds ...