2003 GMC SIERRA 2500HD

Typical onset: 120,000-200,000 mi

Symptoms: white smoke on startup, rough idle, excessive fuel in oil (oil level rising), hard starting when warm, reduced power and black smoke under load

Fix: All eight injectors typically replaced as a set because they fail progressively. Requires cab removal or cutting access holes in firewall; most shops pull the cab (8-12 hours labor). Injectors themselves are $3,000-4,500 for quality Bosch units. This is THE defining LB7 problem.

Estimated cost: $4,500-6,500

Typical onset: 150,000-250,000 mi

Symptoms: harsh or delayed shifts, slipping between gears, limp mode activation, transmission overheat warnings, metal shavings in pan during service

Fix: Internal spin-on filter clogs with clutch material and debris. Requires pan drop and valve body removal to access (4-6 hours). Often caught during routine service at 100k intervals. If ignored, leads to valve body scoring and full rebuild. External filter service does NOT address this.

Estimated cost: $600-1,200

Typical onset: 100,000-180,000 mi

Symptoms: no-start condition, stalling at operating temperature, sputtering under load, fuel pressure dropping below 55 psi, whining noise from tank area before failure

Fix: In-tank electric pump fails, often without warning. Requires fuel tank drop (2-3 hours). OEM AC Delco pumps last longest; avoid cheap aftermarket. Some trucks have dual tanks—verify which feeds engine. Not a gradual failure; usually sudden no-start.

Estimated cost: $500-800

Symptoms: service 4WD light illuminated, unable to shift into 4WD, grinding when attempting 4WD engagement, 4WD engages but won't disengage, clicking noise from transfer case on startup

Fix: Push-button 4WD system uses encoder motor on transfer case and control module (TCCM) under dash. Motor gears strip or module corrodes (especially in salt states). Motor replacement: 1.5-2 hours. TCCM: 1 hour. Diagnosis critical—don't throw parts. Manual-shift transfer cases don't have this issue.

Estimated cost: $350-700

Typical onset: 80,000-150,000 mi

Symptoms: oil leaks from valve covers, oil on intake piping, excessive crankcase pressure, blow-by smoke from oil filler, whistling or hissing from engine bay

Fix: LB7 uses internal crankcase vent passages that clog with sludge, causing pressure buildup and seal failure. Requires valve cover removal and cleaning/drilling passages (3-5 hours). Aftermarket vent filter kits available to prevent recurrence. Catches shops off-guard—looks like gasket failure but cleaning is the real fix.

Estimated cost: $400-800

Typical onset: 80,000-140,000 mi

Symptoms: power steering fluid leak at sector shaft, dripping onto frame rail, low fluid warnings, groaning when turning at low speed, steering wander if fluid gets critically low

Fix: Sector shaft seal fails due to wear and heat cycles. Seal kit replacement: 2-3 hours (requires alignment afterward). Many owners just top off fluid for years; not a safety issue until fluid loss becomes rapid. Full gearbox replacement rarely needed unless internal wear present.

Estimated cost: $300-600

Typical onset: 100,000-200,000 mi

Symptoms: ticking noise on cold start, exhaust leak smell in cabin, visible soot around manifold, noise worsens under load, check engine light (rare unless O2 sensor affected)

Fix: Manifold bolts corrode and snap due to heat cycling. Requires manifold removal and drilling/extracting broken bolts from cylinder head (4-6 hours per side if extractions go poorly). Use quality stainless hardware on reinstall. Driver side is easier; passenger side requires accessories removal.

Estimated cost: $500-1,200