2015 TOYOTA 4RUNNER

Typical onset: 80,000-150,000 mi

Symptoms: Cold-start rattle or knocking for 30-60 seconds that worsens over time, P0418 or P0419 secondary air injection codes, Metal shavings in oil, eventual bearing failure and rod knock, Catastrophic engine seizure if ignored

Fix: The secondary air injection pump can fail and send debris into cylinders, scoring cylinder walls and causing piston slap. Once piston skirts are damaged, it progresses to bearing wear. Requires complete engine rebuild or replacement: 20-30 labor hours for rebuild, 16-20 for used/reman swap.

Estimated cost: $4,500-8,500

Typical onset: 60,000-120,000 mi

Symptoms: Pink fluid puddle under front of vehicle, Transmission slipping or delayed engagement after leak starts, Milky transmission fluid (coolant contamination) if internal cooler also fails, Complete transmission failure if driven after mixing fluids

Fix: External cooler lines crack at the crimp connections to the radiator. If you catch it early, it's just lines (2 hours). If coolant mixes with ATF, you need full transmission flush, possibly torque converter replacement, and radiator. If driven contaminated, full transmission replacement: 8-12 hours.

Estimated cost: $350-800 for lines only, $4,000-6,500 for transmission replacement

Typical onset: 80,000-140,000 mi

Symptoms: Ticking or tapping noise from engine bay that increases with RPM, Exhaust smell in cabin, Visible soot around manifold joints, P0420 catalyst efficiency code sometimes appears

Fix: The 1GR-FE manifolds crack between ports or the studs break off in the head due to heat cycling. Studs stripped in the aluminum head are the real problem—often requires helicoil inserts or head removal for proper extraction. 4-6 hours per side if studs extract clean, 8-12 if head comes off.

Estimated cost: $800-1,800 per side

Typical onset: 70,000-110,000 mi

Symptoms: Gear oil drips on driveway under rear axle, Whining from rear end if fluid gets low, Visible oil on differential cover and pinion area

Fix: Pinion seal hardens and leaks. Requires driveshaft removal, pinion nut torque spec is critical (must not over-tighten or you'll change bearing preload). 2-3 hours labor. Catch it early before the diff runs low on fluid.

Estimated cost: $350-550

Typical onset: 90,000-130,000 mi

Symptoms: Clunk when shifting from Park to Drive or Reverse, Vibration at idle in gear that goes away in Park/Neutral, Visible sag or torn rubber on transmission crossmember mount

Fix: The large rear transmission mount fatigues and collapses, letting the transmission sag and contact the crossmember under load. Replacement is straightforward: support transmission, unbolt mount, swap in new. 1.5-2 hours.

Estimated cost: $250-450

Typical onset: 80,000-120,000 mi

Symptoms: Clunking over bumps from front suspension, Wandering or vague steering feel, Uneven tire wear on inside edge, Play visible when prying on control arm with tire lifted

Fix: Lower ball joints wear faster than uppers due to load. Toyota sells the whole lower control arm assembly (no press-in ball joint available from dealer). Aftermarket press-in joints available but arm swap is cleaner. 2-3 hours per side including alignment.

Estimated cost: $500-900 per side with alignment