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: A/c compressor removal/installation
1. Disconnect the negative battery cable.
2. Discharge the refrigerant from the system. (See RECOVERY.) (See CHARGING.)
3. Remove the right side splash shield and mudguard (L.H.D. only).
4. Loosen the drive belt and remove it.
Caution
If moisture or foreign material enters the refrigeration ...
Mazda 6 Service Manual: Service cautions
HANDLING INSUFFICIENT REFRIGERANT LEVEL
If an insufficient refrigerant level is detected at troubleshooting,
do not charge (add) the refrigerant. Because an accurate amount of
refrigerant cannot be determined from the pressure indicated on the manifold
gauge, never charge the refrigeran ...