Mercedes-Benz M112 (2.6–3.7 V6)

Mercedes-Benz's V6 of the late 1990s and 2000s, sold at 2.6, 3.2 and 3.7 litres and sharing its architecture with the M113 V8 beside it.

It is a three-valve, single-plug-per-cylinder design — the identifying feature of the pair, and the source of their shared complaint: the ignition works hard, and coil and plug failures produce misfires that are cheap to fix and frequent. The engine is durable well past high mileage.

What the V6 has that the V8 does not is a balance shaft, and it is the fault worth knowing about: the sprocket wears, and the engine then reports timing correlation rather than anything that sounds like a balance shaft. The crankcase ventilation system and, on the earliest cars, brittle biodegradable harness insulation account for most of the rest — faults that look electrical because they are.

⚑ It is a family spanning 2.6 to 3.7 litres, and our rows carry the 2.6 and 3.2 across six models. The three-valve head is common to all of them, which is what the characteristic complaints attach to rather than to any one size.