2002 HUMMER H1

Typical onset: 100,000-150,000 mi

Symptoms: Excessive blow-by and crankcase pressure, Coolant in oil or oil in coolant from cracked cylinder heads, Spun main or rod bearings with metallic knocking, Loss of compression across multiple cylinders, Catastrophic overheating leading to warped heads or block damage

Fix: The 6.5L is notorious for cracked heads, failed head gaskets, and bearing failures. Most engines need a full rebuild or short block replacement by 120k-140k miles. Expect 40-60 hours labor for a proper rebuild with machining, new pistons, bearings, rings, head gaskets, and related seals. Many owners opt for a reman long block to avoid the downtime.

Estimated cost: $8,000-15,000

Typical onset: 60,000-120,000 mi

Symptoms: No-start or intermittent stalling, especially when hot, Extended cranking before engine fires, Loss of power under load or complete shutdown while driving, Check engine light with fuel system codes

Fix: The PMD module mounted on the injection pump fails from heat soak. Relocation kits help prevent repeat failures but many techs see the IP itself wear out or develop internal leaks. PMD replacement alone is 2-3 hours; full IP replacement is 6-8 hours including bleeding and timing.

Estimated cost: $400-800 (PMD alone), $2,500-4,000 (full IP)

Typical onset: 80,000-130,000 mi

Symptoms: Transmission fluid leaking from cooler lines or radiator connections, Harsh or delayed shifts when trans is hot, Burnt transmission fluid smell, Coolant contaminated with ATF (pink milkshake in overflow tank)

Fix: The 4L80E transmission cooler lines rust through or the internal radiator cooler fails, cross-contaminating coolant and ATF. Once cross-contamination happens, you're looking at a full trans rebuild, radiator replacement, and cooling system flush. Preventive line replacement is 3-4 hours; post-failure cleanup is 15-20 hours.

Estimated cost: $600-1,200 (lines only), $4,500-7,000 (full trans rebuild after contamination)

Symptoms: Hard starting or no-start in cold weather (below 40°F), Excessive white smoke on cold starts, Wait-to-start light cycles but engine won't fire, Individual glow plugs test open or shorted

Fix: Glow plugs seize in the heads and snap during removal, requiring head removal for extraction. The glow plug controller also fails. Budget 8-12 hours if you break plugs and need to pull heads for proper extraction. Many techs pre-soak with penetrant for days before attempting removal.

Estimated cost: $800-2,500

Typical onset: 90,000-140,000 mi

Symptoms: Loss of power under acceleration, Black smoke under load indicating overboost or underboost, Wastegate rattle at idle, Turbo oil leaks into intake or exhaust

Fix: The GM-8 turbo wastegate sticks or the actuator fails, leading to poor boost control. Oil seals also fail, dumping oil into the intake. Turbo replacement is 6-8 hours including manifold work and oil line replacement. Upgraded turbos are common at this point.

Estimated cost: $1,800-3,200

Symptoms: Hubs won't engage or disengage in 4WD, Clicking or grinding from front hubs during turns, Uneven brake wear or brake fluid leaks at calipers, Spongy brake pedal with no external leaks

Fix: The torque-biasing differentials and inboard brake setup mean brake and hub service is far more complex than typical trucks. Hub rebuilds require special tools and 4-6 hours per axle. Brake jobs often reveal corroded hard lines or caliper issues requiring additional labor. Hydroboost failures also common.

Estimated cost: $1,200-2,500 (hub service both fronts), $800-1,500 (full brake job)

Typical onset: 70,000-110,000 mi

Symptoms: Severe clunking when shifting into gear, Driveline vibration at highway speeds, Visible sagging or misalignment of transmission, Exhaust contact with crossmember or body

Fix: The rubber mounts disintegrate and the crossmember itself can crack from the weight and torque. Replacement requires supporting the drivetrain and is 4-5 hours. Welding crossmember cracks adds another 2-3 hours if you're addressing structural damage.

Estimated cost: $600-1,200

Typical onset: 50,000-100,000 mi

Symptoms: Fuel starvation under load or at highway speeds, Air in fuel system requiring frequent bleeding, Fuel filter clogs rapidly (less than 5,000 miles), Hard starting after sitting overnight

Fix: The mechanical lift pump fails, causing cavitation at the IP and eventual IP damage. Fuel tank contamination from rust and algae growth in diesel is common. Requires tank drop, cleaning, new lift pump, and fuel system flush. Tank service alone is 6-8 hours.

Estimated cost: $400-700 (pump only), $1,500-2,500 (full tank service)