The loudest year in the band, and every free programme that once covered it has expired.

The belt-driven vacuum pump that powers your brake booster loses output over time, and as it does the pedal gets hard and the truck takes longer to stop. Owners describe it as intermittent and frightening: "brake pedal become hard and it will seem like the truck it's not stopping." Recall 19V645 covers it with a free reprogram of the Electronic Brake Control Module so the system can fall back on hydraulic boost. A parts-channel mechanic teardown adds the cheap thing to check first — the vacuum line from the pump to the booster has an O-ring connection that leaks, and if the line wiggles loose at the booster the seal has failed. His warning is worth money: shops often replace the master cylinder or the booster instead, and "in all actuality, it's probably not the real cause." A master cylinder is quoted at over $700.

The 6-speed and 8-speed automatics in this year draw a steady stream of shudder and hard-shift reports: "TRANSMISSION SHUDDERS, LURCHES FORWARD UNCONTROLABLY, AND HARD SHIFTS," and "transmission failure, hard shifting, slipping and loss of power also severe shuddering." Before assuming the worst, rule out the transmission oil temperature sensor. GM wrote a no-charge Special Coverage for 6.2L trucks whose sensor connection causes "rough transmission shifts or hesitation during acceleration," fixed by replacing the transmission wiring harness — and a gen-four Denali owner describes diagnosing exactly that from a P0711 code after his truck felt like it was slipping between first and second. That coverage has expired, but the harness is still far cheaper than a transmission. The genuine failures cluster near 100,000 miles.

The combined transmission-fluid and air-conditioning condenser cracks from thermal cycling and lets the refrigerant out, killing the A/C. GM covered it under Special Coverage 17336 for five years or 60,000 miles on the Yukon and Yukon XL — a window that closed years ago on any 2016 you can buy today. A gen-four Denali owner describes the failure point: "right along this rim, it will usually crack. So, it's pretty easy to see. If you look in there, you can see it moist." A community teardown puts the crack near the mounting brackets. The bill is in the labour: the same owner notes it "would require taking off the whole front bumper and front end and replacing it and having it charged." Run the air conditioning hard on the test drive, in traffic, until the fans cycle.

GM's Special Coverage Adjustment N182198000 describes 5.3L and 6.2L trucks where "one or more of the vehicle's fuel injectors may deliver an improper amount of fuel to the engine," lighting the check-engine lamp, making the engine idle or run rough, and potentially stalling it. Two things about it matter to a buyer. First, the coverage applied only in a listed set of emissions states — California, Connecticut, Delaware, Maine, Maryland, Massachusetts, New Jersey, New York, Oregon, Pennsylvania, Rhode Island, Vermont and Washington — so most owners never had access to it. Second, it is over. A community source confirms the pattern independently for 2015–2017 trucks: "engine vibration, cylinder misfire conditions and hesitation under acceleration."

GM's Special Coverage N182180270 covers 2015–2017 Yukon, Yukon XL, Yukon Denali and Yukon Denali XL vehicles where "stop and tail functions inside the tail lamps may become inoperative," with dealers replacing the lamps at no charge. The reason it is worth knowing about is that it fails intermittently, which makes it almost impossible to self-diagnose. A gen-four Denali owner puts it perfectly: "You'll have people tell you, 'Hey, your brake lights out.' And then you get home and you push on the brakes and you'd say, 'No, they're both working.' But it can be working on and off as that connection isn't [made]." Have someone stand behind the truck while you press the brakes several times, and check again after a drive.

Two documents apply only to the Denali, because in 2016 the 6.2L was a Denali engine in the Yukon range. Customer Satisfaction Program 15638 covers 6.2L engines "built with cylinder head gaskets in which the head gasket stopper ring was off location," which can leak combustion gas into the coolant — GM's own list of symptoms runs through a P0300 misfire code, overheating, an overflowing coolant bottle, milky oil, piston scuffing and, if you keep driving, engine failure. Dealers replaced both head gaskets. Separately, Denalis run Z55 AutoRide air-levelling suspension, and this year's complaint file already carries suspension warnings — "the suspension service lights repeatedly coming on." Check the coolant bottle and the oil filler cap on any 6.2L, and park an AutoRide truck overnight to see whether it settles.

On AutoRide-equipped trucks the failure runs in a predictable order, and two hands-on mechanic teardowns describe it identically. As an air spring ages it leaks, the compressor runs more and more often to keep the bag inflated, and eventually the compressor burns itself out — so you end up buying both. One mechanic's account is the whole lesson: "I remember thinking, that compressor's kicking on at odd times, I should probably do something about that, and then I ignored it like an idiot and then it went bad, so now I gotta replace the compressor too." The free diagnostic takes ten seconds: start the truck and listen. Silence means a dead compressor; a compressor that cycles on and off every few minutes means a bag is leaking. Soapy water on the air springs will show you the bubbles.