2018 GMC Sierra 1500: What to check before buying

Hard, jarring shifts from the 8-speed automatic are the dominant complaint, especially between first and second gear. Reports describe the truck lunging forward on downshifts or when shifted into drive, shuddering, grinding, and dropping into limp mode. Many owners notice it near new, and it worsens with mileage. Fluid changes, software relearns, new torque converters and full transmission replacements are common, and the problem often returns afterward. Four complaints involve crashes, mostly low-speed lunges into objects in parking lots and garages.

Failed or collapsed valve lifters lead this category. They often damage the camshaft and pushrods, and some trucks need a new engine. Ticking, misfires, shaking and sudden power loss at highway speed are the usual symptoms, often with no warning. Some reports link the failures to the active fuel management system. Other patterns include leaking radiators between roughly 47,012 and 59,000 miles, often denied under warranty, plus failed fuel injectors that cause misfires or put gasoline in the oil. Out-of-warranty engine repairs run into the thousands.

Internal engine failure is the main theme. Dealers and mechanics find failed lifters, damaged camshafts, a broken connecting rod and metal shavings, and they usually recommend a replacement engine. Before failure, owners notice hesitation, banging or ticking, shaking and reduced power. Several connect their trucks to federal engine investigations or recalls but find their VIN is not covered. One lifter failure came back after an engine replacement. Fractured exhaust manifold bolts and a leaking AC condenser also appear.

Constant false warnings are common, especially "Service Trailer Brake System" along with StabiliTrak and ABS lights. Wiring faults also appear. The main harness under the truck can separate from its conduit and arc, which leaves the truck unable to start. Rodents chewing the harness knock out locks, wipers and safety systems. A harness routed through the console hinge can be cut. Other reports describe sudden shutoffs at highway speed, repeated battery replacements, a rear window defogger smoking, and one fire that started at the rear of a parked truck.

Power steering cuts out without warning, leaving the wheel very hard to turn at highway speed, over bumps, or in low-speed turns. In some trucks the dashboard and engine also cut out. Repairs, including a replaced steering rack, often fail to stop it. Owners also report the truck pulling left, the steering wheel shuddering at 40 to 55 mph, and tires rubbing the upper control arm at full lock. One crash followed a ball joint pulling out of the control arm on a low-mileage truck.

Two problems dominate. The first is a "Service Trailer Brake System" alarm that sounds over and over, even on trucks that never tow, which owners find dangerously distracting. The second is a "Service Brake Assist" message that comes with a stiff or vibrating pedal and longer stopping distances. Dealers often trace this to a failed brake vacuum pump. Several owners found the problem matched an existing recall but their VIN was not included. One report describes a failed ABS control module.

Few complaints are filed here, but most involve crashes. In one, the airbags did not deploy in a 35 mph collision and the driver suffered a head injury. In another, the steering wheel cover split at the logo during deployment and injured the driver's wrist. Side airbags also deployed with no crash in a driveway, and one deployment filled the cab with smoke. One owner reports waiting on a recall replacement part with no dealer action.

Sunroof glass shatters on its own while the truck is moving, with no impact, and drops shards into the cabin and bed. Dealers send owners to their insurance company instead of covering it. In one report, the spare tire cable broke and the tire fell out at highway speed and damaged a towed camper. Another describes a brake pedal that turned hard and made an air sound, which led to a crash on a low-mileage truck.

The front buckle fails to latch or releases after latching. Rear belts stop locking or retracting, and some get stuck between the seat cushions. One failed middle belt left an owner unable to use a child booster seat. Some failures show up soon after purchase, others around 60,000 miles. Dealers usually replace the buckle receptacle or retractor, and owners pay for it.