Chevrolet Atlas (LLR / LLV)

General Motors' Atlas family — an unusual set of inline four, five and six cylinder engines sharing one architecture, fitted to the Colorado, Canyon, Trailblazer and Hummer H3. The 3.7-litre inline-five is the one most people encounter, and a five-cylinder in a mid-size truck was distinctive even at the time.

The layout is the diagnostic frame: a five-cylinder's firing order and vibration signature differ from a four or a six, which matters when reading a misfire or interpreting a roughness complaint by ear.

Its known failure is the cylinder head, where cracking between the valve seats on a defined range of production let coolant into a cylinder — presenting as coolant loss and misfire, and routinely misdiagnosed as a head gasket. Beyond that, the recurring items are the timing chain and its tensioner at high mileage, and — on the Colorado and Canyon — the usual consequences of working duty in dusty conditions.