Guide How to rebuild 2017 CX-5 Rear brake piston (didn't put into maintenance mode)

I’m new here and am grateful to have found your forum and have spent several hours reading up on changing the rear brake pads. Had I read these tidbits of info instead of incorrectly following a couple of videos on youtube I wouldn’t have had this problem, but I do have some info that may prove helpful to other diy people on rebuilding that piston brake assembly as well as the mysterious c clip....lesssgooo!

Here’s the link to the video:


  1. Changed the front and rear brakes on my wife’s 2017 mazda cx5 grand touring. There was a gnarly grinding sound coming from the brakes that she didn’t tell me about FOR MONTHS. Normally my brakes almost always wear out in the front first. This was not the case so I changed all 4 brake pads.
  2. Fronts were per normal, I always just flip up my calipers and leave the top bolt on when I’m doing the change so you don’t have to zip tie them. No problem here.
  3. Started changing the rear and noticed immediately the left rear rotors had deeply scored the disk. I knew this ahead of time and had bought a new rear rotor. I removed the brakes and tried to turn the piston like you do with every other fugging import car in the world because I had watched a video online on the cx5 and thats what the dude did and the internet is always right….
    1. DUH. I had no idea about putting it into “maintenance mode” until I read the forums and saw some other videos. DUH I also did not realize that you have to do this BEFORE you jack up the car, while fidding with the switches and doing the foot pedal dance I hit the “parking brake on” switch and thus the piston pushed ALL THE WAY OUT. I tried to rethread it with the rubber boot on and it wasn’t going to happen. I tried all kinds of things for about 4 hours as it got dark. Finally, I have rebuilt piston brakes before and decided to go this route.
    2. I removed the motor that runs the parking brake. There are only two allen head screws that hold that in, I believe they are metric thread M6 1.0x30mm. In case you are dumb and lose one like I did, I got two more at home depot. I also unclipped said motor. I unscrewed the brake line and carefully clamped the brake line because it kept leaking.
  4. That mystery c clip you see floating around inside the piston when this happens probably goes on the threaded bolt on that weird robot looking part that is inside the piston. If you carefully screw the clip, it will just screw on. I also noticed there is a obvious couple of spots on the plastic guard on that bolt that is slotted, I believe the raised part of the clip fits in there. I’m pretty sure that is correct because when I was learning how to raise and lower that piston after I screwed it together with the clip on and in the slotted spot, the clip came right off just like when I found it off earlier.
  5. Here is what I did: I carefully screwed that clip on just a bit on the top of the threaded bolt with just a few threads on it. I put the bolt in and carefully screwed it by hand to start it and made sure that raised part of the clip went inside that slot on the plastic piece inside the piston chamber of the caliper.
  6. You only want to screw in the inner piston part just enough to thread that bolt and seat that clip. Then carefully slide the rubber skirt seal down the piston to the bottom. I watched a lot of videos on the guys with mazdas rebuilding their pistons, the easiest way I found by far is to use a screwdriver and CAREFULLY put the bottom the the skirt inside the caliper. If you put clean brake fluid on the bottom of that rubber you can carefully seat it and start to spin it by hand so the whole skirt rotates around and eventually you have seated the entire piston.
  7. On the back of the caliper when the motor has been removed, you’ll see a hex nut shaped piece of metal. Get the socket that fits that for your socket wrench. Here is how the thing works: If you turn that piece of metal clockwise it retracts the piston. If you turn it counter clockwise it raises the piston. What you want to do is crank it CLOCKWISE (that is clockwise if you are looking at it) about five full turns and then push the piston down, you can do this with your hand (wear gloves so the oily brake fluid that is on there doesn’t bind it.) It will go down about a quarter inch. Crank it again. Push it down with your hand. Repeat this until the piston is almost seated. When you get close to the end carefully push the top of the rubber skirt close to the edge of the piston, it will pretty much self seat itself. I fooled around and cranked it up and down and thats how I know that the little clip falls off when the piston falls off. Anyways crank it clockwise and push down until that piston is almost all the way in, now you can put it back together and put the new disk brakes in and it will fit!
  8. Make sure the piston did not rotate, the little cross should be at 12, 3, 6, 9:00 so the bump on the brakes will catch in it.
  9. Remount the parking brake motor, you might have to rotate the motor a little bit to get the hex head to fit correctly. Do not fight it, just take your time and try different angles and it will slide in.
  10. Bleed your brakes per normal. I did not prefill the piston as someone suggested because I already made a big ass mess on my cement that I will be scrubbing off shortly.

On a side note, it is possible to compress the piston without getting the car into “service mode”. I know this because I already had the car up on jacks and could not get it into service mode. I started fooling around with the passenger side rear and took the brake pads out and sure enough they didn’t go back in. YOU MEAN I HAVE TO REBUILD THE FREAKING PISTON AGAIN? No as long as you didn’t turn the parking brake on again, the piston is still threaded.

DO NOT FIDDLE WITH THE PARKING BRAKE SWITCH. Remove rear wheel. Remove parking brake motor. Take the two caliper bolts off and remove caliper (You do not have to take the brake line off, just be careful and make sure it’s not hanging). Remove brake pads.

NOW TO COMPRESS THE PISTON WITHOUT BEING IN SERVICE MODE…(I would not suggest this, I would only do this if you are in a bind because you didn’t do service mode first and are now panicking like I did.)
  1. Open the brake reservoir cap and you will be checking the level periodically. You want it to be a bit low, you can discard some with a turkey baster if it is too high. That is because as you compress the piston the fluid rises and you don’t want it overflowing.
  2. Get the socket that fits that piece of metal and your socket wrench. Crank it a few turns CLOCKWISE (as it is facing you). You cannot use your hand, you will have to use a brake piston compressor, the one I rented at autozone was the fancy one but it wouldn’t fit so I returned it and got this one: (commissions earned)
  3. After you crank on that piece of metal with the socket wrench about five times, use the compressor to slowly compress the piston. It will move down about ¼ inch. AS YOU ARE CRANKING THE SOCKET MAKE SURE THE PISTON DOESN’T SPIN BECAUSE SOMETIMES IT WILL START TO DO THIS. Then crank on the socket another few times and again compress the piston with your tool. You keep repeating this until the piston has lowered enough that you can slide it over your new brake pads. Install pads per normal.
  4. Bolt on the caliper again, then bolt on the motor being careful that you aligned that hex metal up with the motor female part. If you do it correctly it will easily slide back in.

Obligatory rant: I have no idea why car manufacturers are going electric parking brake instead of regular parking brake, you cannot use it in an emergency if your brakes fail because that electric parking brake is all or nothing, there’s no way to feather it like you can with a pull ebrake! Also, I hate whatever fugs posted those videos online saying you should turn the piston to retract the newer mazda cx5 brakes!!!

One last note. At first the left rear parking brake wasn’t engaging. I knew this because when the car was up on the stands and I was done I tested both sides. I tested the motor on that side with 12v (yes I used a 9v battery to energize the solenoid) and it works fine. I also used my multimeter to test current coming from the harness to the parking brake motor and I am NOT getting 12v when the switch is pushed down or pulled up. I checked the fuses and they were good. What happened was I had dropped the caliper assembly when I was fiddling with it in the dark and it unplugged at that other spot further up the harness right before where the harness connects to the brake motor. It wasn’t the square clip, it was the rounded clip where the wires sort of come together. Once reconnected I was back in business.

Also if you lost one of the allen wrench head metric bolts like me, here's the bag I got at home depot.

I hope this info helps someone else in the future, although I really hope no one has to go thru this AS LONG AS THEY DID MAINTENANCE MODE first!!
Nice write up to fix a problem many have experienced. Thanks for taking the time to help others 👍

With all the various warning labels on the car and in the manual, how about a stamp in the caliper bracket... "WARNING ! MAINTENANCE MODE TO SERVICE" 🤷‍♂️

Also, instead of the hoky-poky dace to get it into maintenance mode, how bout a check-box in maintenance section of infotainment screen? Mazda? Please? Lol
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Hey Oakpwr, great write up! I had the same issue this weekend and ended up doing pretty much exactly as you describe! Brakes working fine. I wish I'd seen your post it would have saved me a few hours of "oh sh!t" "WTF" ... :) Thanks