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: Outside Mirrors
WARNING
Be sure to look over your shoulder before changing lanes: Changing
lanes without taking into account the actual distance of the vehicle in the convex
mirror is dangerous. You could have a serious accident. What you see in the convex
mirror is closer than it appears.
Mirror type
Flat ...
Mazda 6 Service Manual: Dual proportioning valve inspection (without abs)
1. Connect the SSTs to the brake pipes as shown in the figure.
2. Bleed the air from the brake system.
3. Measure the fluid pressure of the master cylinder and the rear brake.
If not within the specification, replace the dual proportioning valve.
Fluid pressure
...