2002 GMC ENVOY

Typical onset: 120,000-180,000 mi

Symptoms: Sudden heavy knocking or ticking from lower engine block, often after cold start, Low oil pressure warning, metal shavings in oil during change, Catastrophic loss of power, engine seizure if driven after knock begins

Fix: Lower-end bearing failure requires either short-block replacement (12-16 hours) or full engine swap (14-18 hours). Machine work on crank journals rarely cost-effective due to labor depth. Most shops recommend reman or junkyard engine.

Estimated cost: $3,500-6,500

Typical onset: 80,000-140,000 mi

Symptoms: Pink or milky transmission fluid (coolant intrusion via leaking internal cooler), Erratic shifting, slipping, or no movement after cooler line rupture, Coolant loss with no visible external leaks, transmission overheating

Fix: External cooler lines rust through (1.5 hours to replace), but internal radiator cooler failure contaminates trans fluid and destroys clutch packs. Requires transmission rebuild or replacement (8-12 hours) plus new radiator and full flush of cooling system. Always replace external cooler lines preemptively during any radiator work.

Estimated cost: $2,800-5,200

Typical onset: 70,000-120,000 mi

Symptoms: Service 4WD message on dash, inability to engage or disengage 4WD modes, Grinding or clicking from transfer case during mode changes, Stuck in 2WD or 4WD with no ability to shift between modes

Fix: Encoder motor or mode actuator motor on transfer case fails (2.5-3.5 hours to replace both). These are external bolt-on units. Sometimes requires reprogramming or relearning procedure with Tech2 scan tool after replacement.

Estimated cost: $600-1,200

Typical onset: 100,000-150,000 mi

Symptoms: White smoke from exhaust, coolant loss with no external leaks, Misfire on adjacent cylinders (common on 3-4 or 4-5), Overheating, bubbling coolant reservoir, combustion gases in cooling system

Fix: Head gasket failure on 4.2L I6 requires both heads to be removed, inspected, and resurfaced (10-14 hours). Often find warped heads requiring machine work ($150-300 per head). If caught late, can damage head surface beyond spec requiring replacement heads.

Estimated cost: $2,200-3,800

Typical onset: 60,000-100,000 mi

Symptoms: Loud clicking or ticking from behind dash, especially on startup or temp changes, No heat or AC in certain zones, air blows from wrong vents, Temperature control works on one side only (if dual-zone equipped)

Fix: Multiple actuators control blend and mode doors. Clicking is stripped gear inside actuator (1.5-2.5 hours per actuator depending on location). Driver-side temp actuator requires partial dash removal. Mode door itself can break, requiring deeper dash work (4-6 hours).

Estimated cost: $250-900

Typical onset: 90,000-140,000 mi

Symptoms: Whining or howling from front end during acceleration or coasting, Clunking when engaging 4WD, vibration at highway speeds in 4WD, Metal shavings in front diff fluid during service

Fix: Front differential bearings wear due to lack of maintenance (fluid rarely changed). Requires diff teardown and bearing replacement (4-6 hours). If caught early, bearing service is sufficient; if neglected, ring-and-pinion or carrier damage requires full rebuild or replacement unit.

Estimated cost: $800-2,400

Typical onset: 100,000-160,000 mi

Symptoms: Hard starting when hot, long crank before firing, Stalling at idle after deceleration, surging under light throttle, Check engine light for lean codes (P0171/P0174) with no vacuum leaks found

Fix: In-tank fuel pump assembly fails or pressure regulator leaks internally, causing low fuel pressure. Requires tank drop and pump replacement (2.5-3 hours). Always check fuel pressure before condemning pump—filter clogs easily if not changed every 30k miles on this platform.

Estimated cost: $600-1,100