2004 HUMMER H1

Typical onset: 80,000-150,000 mi

Symptoms: Sudden loss of power, heavy knocking or rattling from engine block, Metal shavings in oil, oil pressure drops dramatically, Coolant mixing with oil (milky dipstick) if head gaskets also fail, White or blue smoke on cold start that doesn't clear

Fix: Complete engine rebuild or short block replacement required. Typical rebuild includes pistons, rings, main bearings, rod bearings, often crankshaft machining or replacement. Figure 40-60 hours labor for full teardown, machine work, and reassembly. Many owners go with reman long-block to save time.

Estimated cost: $8,000-15,000

Typical onset: 100,000-180,000 mi

Symptoms: Hard starting, long cranking before engine fires, Rough idle, poor throttle response, black smoke under load, Stalling at idle or when coming to a stop, Check engine light with fuel delivery codes (P0XXX fuel system)

Fix: Injection pump replacement is the only real fix—rebuilds rarely last. DS4 electronic pumps are finicky and water-sensitive. Factor 6-8 hours labor for R&R, plus fuel system bleeding and priming. Always replace fuel filter and water separator at same time.

Estimated cost: $2,200-3,800

Typical onset: 90,000-140,000 mi

Symptoms: Coolant loss with no visible leaks, pressurized overflow tank, White exhaust smoke, sweet smell from tailpipe, Engine overheating, especially under load or towing, Oil contamination with coolant (check dipstick and underside of oil cap)

Fix: Both heads typically need to come off—rarely see just one side fail on the 6.5L. Heads should be pressure tested and milled flat. Upgrade to MLS (multi-layer steel) gaskets and ARP studs strongly recommended to prevent repeat. 18-24 hours labor for both sides including cleanup and reassembly.

Estimated cost: $3,500-5,500

Symptoms: Sudden stalling while driving, often when engine is hot, No-start condition, cranks but won't fire, Intermittent starting issues that come and go, Dies and restarts after cooling down for 20-30 minutes

Fix: The PMD is a known Achilles heel on DS4-equipped 6.5L engines—heat kills them. Relocate the module away from injection pump to remote cooler location (many kits available). Takes 2-3 hours. Always carry a spare PMD in the truck. This is a when-not-if failure.

Estimated cost: $400-700

Typical onset: 60,000-120,000 mi

Symptoms: Transmission fluid puddles under truck, red or brown fluid, Transmission overheating, slipping under load, Fluid level dropping rapidly, burnt smell from trans, Hard shifts or delayed engagement when low on fluid

Fix: Steel lines rust through where they route near frame. External cooler often develops pinhole leaks. Replace lines and upgrade to auxiliary trans cooler for towing. Figure 4-6 hours for lines and cooler replacement depending on rust and access.

Estimated cost: $800-1,500

Typical onset: 80,000-150,000 mi

Symptoms: Hard starting in cold weather, excessive white smoke on startup, Long cranking time before engine fires, Check engine light with glow plug circuit codes, One or more glow plugs swelled and seized in cylinder head

Fix: Glow plug controller (module) fails, or individual plugs swell and break off in the head. If plugs are seized, removal can require head removal and drilling/extraction. Prevention: replace plugs every 100k as maintenance item. Budget 3-5 hours for controller and all 8 plugs if heads are accessible, 20+ hours if extraction required.

Estimated cost: $600-1,200 (accessible), $3,000-5,000 (extraction)

Typical onset: 70,000-130,000 mi

Symptoms: Gear oil dripping from front axle or transfer case, Low fluid levels found during service, Oil on inside of wheels or undercarriage, Whining noise from front end if fluid runs very low

Fix: Front axle and transfer case seals weep over time, especially if truck sees water crossings or mud. Replace input/output seals, check vent tubes aren't clogged. 3-4 hours labor depending on which seals are leaking. Not urgent but don't let differentials run dry.

Estimated cost: $400-900