Outdoors_Guy_88

Much Thanks! Removing this connector was way harder than it should have been. Sliding that long stick over until it clicked was not obvious, because it flexed so much, I didn't realize that it actually clicked open at some point. GM needs a free video course on all of their "quick-release: connector types.

Can anyone easily describe how to remove the fan motor plugs on a 2015 GMC Sierra? They are upside down and invisible when I am trying to remove them and I obviously cannot get them to release. Is there a tab or "ears" to push, plug, squeeze, depress or a clip to remove before removing them? I cannot get them to release and I can't really see any mechanism. There is also a white/grey plastic stick coming out. Do I need to do anything with that or is that only to help guide reassembly?

I am surprised too. Out of the many (>10) vehicles I've owned over the last 35 years, (most of them being more than 10 years old), I never had a brake line fail in that manner. They usually develop a leak, start dripping, and lose pressure. You would think they would know how to make a flexible brake line that lasts more than 8 years.

Yes, mine has the factory installed brake controller in the dash and factory installed towing mirrors. Relevant RPO codes I have: MYC, Z82, Z85, Z88, but no NHT listed. Is this still 84207656?

I have a 2015 GMC Sierra 1500 Extended Cab 4WD 6 sp. with a 5.3L-Gas - Work truck package with the factory installed towing package. Now, I have developed the dreaded coolant leak crack in the radiator. I located the thermostat upgrade to prevent thermocycling. There seems to be a couple different radiators listed for this truck. 84207656 and 84207654 both seem to be correct on GM parts websites. Anyone know the proper fitment? Any way to confirm before pulling the old radiator out?

Problem solved. Bad flex lines on both front brakes at 60 k miles. Replaced flex lines, calipers (solid rubber-like particles were coming out with the fluid from the driver side bleeder, so I didn't trust them and replaced the calipers), (and also replaced the fairly new rotors and pads due to overheating the sticking pads caused). Pads were probably OK, but decided not to chance it. The driver side flex line was so constricted that no fluid would flow by gravity down from the master cylinder when I pulled the calipers - It did drip at the rigid line once I pulled the bad flex line. Replaced it all, bleed the system, gravity, first, then the 2-person method and good to go. Still working after 2 days driving.

If I accelerate to 65 mph and then slow down immediately, this doesn't happen. If I drive 10 miles on the highway and then slow down, the pedal pulsates until the brakes cool off. Driving at 40 mph or less doesn't seem to heat them up to cause vibration. Driving 1/2 hour at 55 mph just starts to cause it. Driving several miles at 65 mph causes it whenever I exit. (This is cruising and then gentle braking on the exit ramp, not hard braking). They pulse/vibrate (like a warped disc) when I am slowing down on an exit ramp and at the first stop or two. I get out and I can feel the heat coming off of them and the stock steel wheels are hot to the touch. I also checked with an IR gun. If I pull over and stop for 5-10 minutes, the pulsation is gone. When I drive 10 miles in stop and go city traffic they don't seem to get hot (just warm like normal brakes) and no pedal vibration, even though I am actually using the brakes more. Seems they only drag enough to generate significant heat at highway speeds. Like they just aren't quite releasing.

@KARNUT Any good way to tell if it is the flexible brake lines or the calipers? I'll definitely replace the lines, but I hate to trash good calipers, because they seem to retract smooth without binding when I press them back in. The "Hill Start" assist system could possibly be another bad item. If that system can apply the brakes, then it also has the possibility of not releasing all the way. Anyone know if Hill Assist is front or rear or both? (Or any troubleshooting)?

Thanks for the suggestion. Pads and rotors are all OEM (They are only 1 year old.) and calipers are original. I pulled the calipers and pads about 3 months ago due to the same problem and checked the fit in the shims and greasing (for debris and dirt. Still moved well and only 1 caliper pin was a little sticky. I also pressed the caliper pistons in at that time and they move fine (and no leakage) I now have found several posts on here now about front brakes freezing. So it appears to be a common problem. I am now suspecting bad flex lines or something in the hydraulic system. Also strange how it happened to both front brakes at the same time.

2015 K1500 Sierra with 5.3L Driving around town in stop and go traffic, my brakes seem fine. Nice smooth firm pedal. If I get on a highway and drive more than 10 miles and as I slow down to get off at an exit, I get brake pulsation, like a warped rotor. I check and only the front brakes are hotter than usual, but not smoking. I am guessing slightly overheated brakes in front, (but I was cruising on the highway and not using them). I don't notice and real dragging or pulling to one side. Everything seems OK at low speeds. No pedal pulsation and overheating after driving a couple miles under 40 mph. I already pulled both front calipers and pads. I removed, cleaned and regreased the calipers and caliper pins with the green high-temp caliper grease. Only 1 was a little sticky. Pads were good. I reassembled and still the same problem persists. Funny how it seems to be both front wheels. The drivers side seems slightly hotter. Any other parts that I could check why the fronts seem to be getting hot? Brake fluid level is good, clean, and not low or losing fluid. Suggestions where to look next? I have a new set of OEM pads and rotors, but I am reluctant to put them on, because nothing looks wrong with the current ones. They are at 75% thickness.

I finally had to replace my stock 2015 thermostat due to thermocycling occurring since around November (between about 190-210 F) with changes in throttle load. After the swap it ran rock stable again at 210 F. I have changed many thermostats over the years (usually failed open or failed closed), this is the first that thermocycled noticeably with out sticking in one position. My question: I noticed there is an extra coil spring and little plunger off the bottom of the "bracket" that supports the main spring and traditional thermostat. Anybody know the purpose of that extra spring and plunger? BTW, I tried heating the defective thermostat in boiling water and the main thermostat opened as it should, but that spring/plunger device on the bottom didn't appear to do anything (maybe the cause of the failure). Ideas?

Thanks! I'll definitely have to try this.

Yep! That's next.

The caliper bolts fit on the rear rotors, but too big diameter for the 2 tapped removal holes front rotors. I just tried a M10x1.5 bolt and it only goes about two turns, so almost, but not quite correct size.

I have tried hammering around the rotor, hitting on the front side and back side, and vibrating around the lug bolts with an air hammer. These rotors are stuck on good. I'll have to try the bracket bolts (or even longer bolts) and push from the back side, but I am worried about the strength of those "ears" that hold the bracket on. Yes, I'll be sure to clean up the hubs and put high-temp, anti-seize grease on them before the new rotors.