The 2018 Highlander is generally solid but suffers from a catastrophic D-4S fuel system defect on the V6 that can destroy engines, plus some transmission cooler and hybrid-specific issues. The 2.7L I4 is nearly bulletproof but underpowered.
D-4S Fuel System Contamination (V6 models) - Engine Killer
Occasional · high severityTypical onset: 30,000-80,000 mi
Symptoms: Metal shavings in oil during routine change, Sudden loss of power or rough running, Check engine light with multiple misfires, Fuel pump recall (NHTSA) linked to metal debris in fuel system
Fix: Low-pressure fuel pump impeller disintegrates, sending metal through injectors into cylinders, scoring cylinder walls and destroying bearings. Requires complete engine rebuild or replacement. Toyota extended warranty to 10yr/150k on some VINs but not all 2018s covered. 40-60 hours labor for short block or full rebuild.
Estimated cost: $8,000-15,000
Transmission Oil Cooler Line Leaks
Common · medium severityTypical onset: 60,000-100,000 mi
Symptoms: ATF drips or puddles under front of vehicle, Transmission temperature warning light, Pink or red fluid visible near radiator area
Fix: Cooler lines corrode at crimp fittings or cooler itself develops pinhole leaks. Lines run along subframe and collect road salt. Replace both lines and flush cooler if contaminated. 2-3 hours labor plus fluid.
Estimated cost: $400-800
Transmission Mount Failure (All models)
Common · low severityTypical onset: 70,000-120,000 mi
Symptoms: Clunk when shifting from Park to Drive or Reverse, Vibration at idle in Drive with brake applied, Excessive engine movement visible from engine bay
Fix: Rear transmission mount (torque strut) tears internally. Toyota uses hydraulic mounts that deteriorate faster in hot climates. Replace mount, sometimes both engine and trans mounts if rubber is cracked. 1.5-2 hours labor.
Estimated cost: $300-600
Hybrid Inverter Coolant Pump Failure (Hybrid only)
Occasional · high severityTypical onset: 80,000-140,000 mi
Symptoms: Red triangle warning light with multiple codes, Reduced power or refusal to start, Whining noise from rear of engine bay, Hybrid system overheat warning
Fix: Electric coolant pump for inverter fails (bearings seize or impeller breaks). Inverter overheats and shuts down hybrid system. Pump is buried behind intake manifold. 4-6 hours labor, must drain hybrid coolant and bleed system carefully.
Estimated cost: $1,200-2,000
Brake Booster Vacuum Pump Check Valve (Hybrid)
Occasional · medium severityTypical onset: 50,000-90,000 mi
Symptoms: Hard brake pedal, especially after sitting overnight, Hissing noise when pressing brakes, Check engine light with P0533 or P050A codes, Linked to NHTSA recall on some VINs
Fix: Hybrids use electric vacuum pump since engine doesn't run constantly. Check valve or pump itself fails, losing vacuum assist. Replace pump assembly and check valve. 2-3 hours labor.
Estimated cost: $600-1,200
Fuel Injector Carbon Buildup (V6 D-4S)
Common · low severityTypical onset: 60,000-100,000 mi
Symptoms: Rough idle when cold, Hesitation or stumble on acceleration, Misfires on cold starts (P0300-P0306 codes), Reduced fuel economy
Fix: Direct injection creates carbon deposits on intake valves since fuel doesn't wash them. Requires walnut blasting or manual scraping of valves. Some techs add port injection cleaning. 4-6 hours labor to remove intake manifold and clean all six cylinders.
Estimated cost: $600-1,200
I'd buy a 2018 Highlander Hybrid or 2.7L I4 if fuel pump warranty is confirmed applied and transmission service records exist; avoid non-covered V6 models unless priced $3k-5k under market to budget for potential engine replacement.
AI-assisted summary drawn from NHTSA recall data, our labor-times database, and platform knowledge. Not a substitute for a pre-purchase inspection on a specific vehicle.