It's neglect, nothing else, salt corrosion and lack of lubricant, the pistons corrode and seize in place as do the caliper sliders, unfortunately this is something ignored by most car makers in their service schedules, but then we can't have cars lasting like those gems from the 90's can we, nor could we have fleet/lease buyers costing proper servicing into their calculators unless every maker did the same, cynical yes but how it is.

Calipers need to be stripped of pads, cleaned inspected and lubed up correctly as they are re-assembled at least every other year, and if the vehicle is prone to this make that an annual thing, on Outlander don't forget to remove the rear disc/drum to inspect and lube the parking brake shoes.

Washing winter salt off regularly helps too, not just the brakes but the whole underbody.

Your present calipers might free off if you get a proper mechanic on the job now, but even if you have all new calipers they still need servicing or you will be down this path again in another couple of years.

Forget dash faults,

Get the ABS ECU scanned for faults to be sure.

As to callipers the fronts repond well to "Red Rubber" grease on the pistons and seals.

Formulated for just this thing.

As to the rears I usually find this to be a result of some b***** in the past tightening up the hand brake cable for MOT time.

Which does work in the short term and you get a certificate but completely b*****s up the calliper self adjust system so the rear calliper activation crank does not move enough and so siezes.

My procedure is first slacken the h/brake cable then remove from calliper/s,

then wind back the calliper pistons until fully back in,

Fit pads and refit callipers THEN crank the calliper lever back and forward to advance the piston out the calliper and take up the slack.

Doing this you'll soon discover if the calliper is servicable or not.

Once done then re attatch the cables and adjust h/brake free play to 4-6 notches depending.

Now this might seem a right hoo ha but I seldom need to fit expensive rear callipers and you the customer isn't charged for new parts.

So I'll repeat myself,

OVER TIGHTENING HAD BRAKE CABLE ADJUSTMENT WILL ONLY MEAN SCRAP CALLIPERS!!