2020 GMC Terrain: What to check before buying

Brake assist disappears without warning, leaving a rock-hard pedal that takes both feet or full body weight to stop. A Service Brake Assist message, a check engine light, or a ticking noise sometimes comes first, but many failures arrive with no warning at highway speed. Four complaints involve crashes. Dealers most often blame the brake vacuum pump, and some owners also have the booster, booster sensor, or vacuum pipe replaced, sometimes more than once. Failures cluster between about 37,000 and 71,000 miles. In several cases the pump breaks at the camshaft and ruins the engine.

Hesitation from a stop is the most common report. The pedal goes to the floor, nothing happens for several seconds, and then the car lurches forward, often while pulling into traffic. Dealers often find no code. Other complaints describe vacuum pump failures that break the timing chains, full engine rebuilds or replacements, heavy oil burning with misfires, and reduced power linked to the intercooler. Some owners also report a front-end wobble or clicking under throttle and the transmission dropping into neutral or park while moving. Several say recalls on similar GM vehicles leave out their VIN.

Infotainment glitches lead this category. Screens go black, the radio jumps to full volume, and Bluetooth and USB connections drop. Backup cameras fail to a blue screen, sometimes even after the camera is replaced. More serious reports describe the car shutting down at intersections, shifting into park at speed with the steering locked, and an anti-theft fault that blanks every gauge on the interstate. Repeated Service Brake Assist warnings with a stiff pedal also show up here. Auto Stop draws complaints because it cannot be switched off and delays pulling away.

Sudden engine destruction is the main theme. The vacuum pump seizes or a camshaft end cap comes loose, the cam skips timing, and the engine is ruined, sometimes at highway speed with no prior warning. Other reports describe oil loss requiring a new engine while still under warranty, metal shavings inside the engine, and shaking with a flashing check engine light. A second pattern is turbo underboost code P0299, with power loss in cold or foggy weather traced to moisture in the charge air cooler. Fuel pump module stalls and hesitation from a stop also appear.

The engine stalls without warning and will not restart, most often because the fuel pump control module has failed. Stalls happen in traffic, and one stranded car could not be shifted into neutral to be pushed aside. A battery saver message or code P129F can accompany the failure, and one owner paid $850 for the module. Some owners say a federal notice covers this failure but their VIN is excluded. Other reports describe the throttle going dead from a stop and a tank that takes only a few gallons while the gauge reads full.

The car stalls or refuses to restart, and the cause is traced to the fuel pump or fuel pump control module. Messages such as Low Battery or Start the Vehicle often appear afterward. Some cars lose power while moving with the check engine light on, and others fail to start after refueling. Most reported failures fall between about 42,000 and 45,175 miles, with one at 88,000. Every case ends with a tow. One owner links the failure to a fuel system recall that does not include their VIN.

Stalling or power loss on acceleration, mostly after a stop, is the core problem, and owners describe near misses at intersections. Without a stored code, dealers often cannot find the fault and keep cars for weeks. Other reports describe the car slowing on the highway with the check engine and traction lights on, one ending in an engine rebuild at about 25,000 miles. Adaptive cruise shuts off on its own, and one owner reports the cruise setting itself far too high. A hard brake pedal on the highway accounts for the 2 injuries listed.

Automatic emergency braking fails in both directions. In one crash report, it did not engage before a collision. Another car applies its brakes on its own and shows hill descent messages on level ground, with under 4100 miles on the clock. A third report says none of the safety features have ever worked. The risk runs both ways: the system can fail to brake when a car is ahead and can also brake when nothing is there.

Water comes in through the sunroof drains, soaking the carpets and pooling in the spare tire well. In one case mold grew inside the cabin, and the owner reports a respiratory illness, which is the single injury listed. Dealers unclog the drains, replace the carpets, and swap sunroof parts, but the leak comes back. The other complaint describes the rear camera failing with a Service Rear Camera System message at about 53,500 miles.