Engine

COMMON PROBLEMS: Oil Consumption, Carbon Buildup, Rough Idle, Oil Leaks, Misfires

Higher-mileage Highlander V6s can start using a bit of oil, so checking the dipstick now and then keeps you from running low. On the direct-injection versions, carbon builds up on the intake valves, and eventually you feel it as a stumble or an uneven idle. As the gaskets age they seep, which is where the driveway spot and the warm-oil smell come from. A worn coil or plug will set off a misfire and a dash light. If that light is flashing, don't wait, a live misfire can wreck the converter fast.

Cooling System

COMMON PROBLEMS: Water Pump Leaks, Coolant Loss, Thermostat Failure, Overheating, Radiator Leaks

The cooling parts are reliable on these, but years of heat catch up with them. The water pump seal gives out and starts to seep. A hose splits, or the radiator cracks at a plastic end tank, and now coolant is getting out somewhere. Often the sweet smell reaches you before the puddle does. A thermostat that sticks sends the gauge the wrong way, running hot or never fully warming up. The move is to catch a small leak early, because an overheated V6 this size is a much bigger repair than a hose.

Fuel System

COMMON PROBLEMS: Fuel Injector Issues, Hard Starting, Rough Idle, Hesitation, Check Engine Light

You don't see much fuel trouble on a Highlander, but injectors and pumps don't last forever. Once one starts to slip, the symptoms show up fast. It cranks a beat too long before it fires. It shakes at the light. You hit the gas and there's a pause before it responds. A dirty injector or a fading pump can trip the check engine light on top of that. It feels a lot like an ignition problem, so we run the tests instead of swapping coils and hoping.

Electrical System

COMMON PROBLEMS: Battery Drain, Alternator Wear, Warning Lights, Sensor Faults, Starting Problems

Newer Highlanders carry a lot of electronics, so there are more spots where something can act up. A battery that's flat by morning from a draw you can't see. Or one that keeps dying because the alternator stopped charging it. Warning lights that flicker on and off. A sensor that glitches and leaves the engine running strange. It might be minor, a worn battery or a corroded ground. It might take some real hunting. There's no telling until we look.

Suspension

COMMON PROBLEMS: Strut Wear, Control Arm Bushing Wear, Clunking Noise, Uneven Tire Wear, Rough Ride

A fresh Highlander rides soft and quiet, which is why a change stands out. Struts wear in slowly, and the clue is a front end that keeps bouncing or floats over dips instead of settling down. Bushings and sway bar links loosen up too, knocking over bumps or as you turn into a driveway. Once those parts wear, the alignment drifts, the tires wear unevenly, and the ride gets rougher. On a rig this heavy that hauls people all week, a small fix caught now keeps a tire bill from landing on top of it later.