The brake-vacuum-pump cluster hits its most concentrated point — the last of the loud Terrain years.

The reason the brake issue above is rated as severely as it is. An independent used-car dealer who has handled twenty-odd second-generation Terrains explains that the vacuum pump "can freeze up, and then if that happens it can take out vital engine parts", citing other dealers whose sold cars lost the pump and then, in his words, "all of a sudden the engine was gone". A 2018 Terrain owner in the federal file reports precisely this outcome — vacuum pump failure causing engine damage, with the car immobilised for six weeks waiting on a camshaft. The dealer's own advice is the practical version: if the pedal is hard to press, that is the vacuum pump, and it needs looking at immediately rather than at the next service. On a 2020 the original powertrain warranty is gone, so there is no safety net behind it.

The second recurring theme. The 1.5T drops into limp mode with an "engine power reduced" message, sometimes tied to the charge air cooler outlet duct disconnecting under boost, sometimes to the turbocharger itself. Unlike the 2019, this model year got no emission recall and no free support program for the duct, so a 2020 with this symptom is an owner-paid diagnosis. Cold weather makes it worse: GM's Service Update covering 2018 to 2022 describes ice or sludge accumulating in the charge air cooler or crankcase ventilation system below roughly 0°F, and a companion bulletin covers fault codes P0299 and P0234 from moisture freezing in the turbo wastegate solenoid. A mechanic source describes the outcome bluntly — the ice blocks airflow and the car loses all power. Any reduced-power message in the history deserves a scan before you buy.

GM issued a Service Update covering the 2020 and 2021 automatic transmission, where a clutch spring retaining ring may not be fully seated. Cars with the condition set fault code P0747 and light the check-engine lamp. A Service Update is a free dealer repair that stops short of a formal recall, so it costs nothing if the car qualifies — but it will not have been done unless someone asked. Combine this with the general second-generation transmission complaints in the file: harsh shifts, hesitation and delayed engagement, some of it software. Drive from a standstill repeatedly in stop-and-go conditions rather than judging it on a highway run.

A persistent background complaint across the second generation. The centre screen freezes or goes black, and the reversing camera intermittently stops displaying. A mechanic source who sells these regularly says it is one of the problems he sees most often, and that it is usually a software fault cured by an update rather than a hardware replacement — which is worth knowing before a dealer quotes for a new display. Test the screen and the reversing camera repeatedly during a long test drive, since the fault is intermittent and a five-minute drive will often miss it.