Engine

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

Some Highlander V6s start using a bit of oil as the miles climb, so a check between changes keeps you from running low. The direct-injection engines cake carbon onto the intake valves over time, and that shows up as a stumble or a lumpy idle at the light. Gaskets harden and seep, leaving a spot on the driveway or that hot-oil smell after you park. A tired coil or plug throws a misfire and lights the dash. A flashing light is the one to jump on, since a live misfire can cook the converter fast.

Cooling System

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

The Highlander cooling system is dependable, but heat wears it down over the years. The water pump weeps at the gasket as it ages. Hoses crack, or the radiator splits at a plastic tank, and either one starts a slow leak you might smell before you see. A stuck thermostat sends the temperature the wrong way, too hot or never quite warming up. Catch a small leak early. Let it run and it turns into an overheat, and on a V6 this size that's a far bigger bill than a hose.

Fuel System

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

Fuel trouble on a Highlander is uncommon, but the injectors and pump still age. And when one starts to go, you feel it. Long crank in the morning before it catches. A shake sitting at the light. That flat spot where you press the gas and nothing happens for a beat. A dirty injector or a weak pump can trip the check engine light too. Thing is, it feels a lot like a bad coil. So we test it instead of throwing parts at it and hoping.

Electrical System

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

Newer Highlanders pack in a lot of electronics, so there are more spots for a gremlin to hide. Battery dead in the driveway from a drain you can't see. Or it keeps dying because the alternator quit charging it. Lights that blink on, then off. A sensor that faults and leaves the car running weird. Could be nothing, a worn battery, a loose ground. Could be something that takes real digging to find. You don't know until you look.

Suspension

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

A Highlander rides soft and quiet when the suspension is fresh, so you notice when that changes. Struts go slow, and the giveaway is a front end that bounces or floats over dips instead of settling down. Bushings and sway bar links wear too. They knock over bumps, or turning into the driveway. Worn parts drag the alignment off, so the tires wear funny and the ride turns rough. On a heavy SUV that hauls people all week, catching it early keeps a small fix from becoming a tire bill on top.