2000 GMC SONOMA

Typical onset: 80,000-150,000 mi

Symptoms: Transmission fluid pooling under vehicle, Pink fluid on ground (ATF mixing with coolant), Transmission slipping or delayed engagement, Milky pink fluid in radiator overflow tank

Fix: The steel cooler lines running to the radiator rust through at the frame mounts or where they crimp into fittings. If ATF gets into coolant or vice versa, you're looking at transmission flush, radiator replacement, and new lines. Preventive line replacement is 2-3 hours; full contamination cleanup adds 4-6 hours total with trans service.

Estimated cost: $400-800 preventive, $1,200-2,500 if contamination occurs

Typical onset: 100,000-150,000 mi

Symptoms: Coolant loss with no visible external leak, White smoke from exhaust on cold start, Rough idle or misfire when warm, Oil looks milky or coolant smells like exhaust

Fix: The composite gasket between upper and lower intake manifold deteriorates, allowing coolant into the crankcase or combustion chambers. Requires intake removal, gasket set, and often new injector O-rings. Book time is 5-7 hours. Use Fel-Pro multi-layer steel gasket set, not OEM composite.

Estimated cost: $800-1,400

Typical onset: 90,000-140,000 mi

Symptoms: No-start condition with cranking but no fuel pressure, Stalling at idle or under load, Erratic or stuck fuel gauge, Whining noise from fuel tank

Fix: The in-tank fuel pump assembly fails, often taking the level sender with it. Requires dropping the fuel tank. 2-3 hours labor. The fuel filter is also a common culprit before 100k—external inline filter clogs from tank sediment. Filter replacement is 0.5 hour and should be done every 30k on these.

Estimated cost: $450-750 for pump assembly, $80-150 for filter

Typical onset: 120,000-180,000 mi

Symptoms: Hard starting especially when hot, Severe misfires on multiple cylinders, Black smoke and rich fuel smell, Loss of power and poor fuel economy

Fix: The Central Sequential Fuel Injection poppet nozzles leak or clog internally. Requires upper intake removal to access the central spider unit. 4-5 hours labor. Upgrade to MPFI conversion kit if available, or replace with updated CSFI unit. Often done alongside intake gaskets.

Estimated cost: $700-1,200

Typical onset: 90,000+ mi

Symptoms: ABS warning light illuminated constantly, No ABS function during braking, Traction control disabled message, Speedometer erratic or non-functional

Fix: Kelsey-Hayes 4WAL ABS system is notoriously problematic. Wheel speed sensors corrode at connectors (1 hour each to replace), or the EBCM module itself fails. Module replacement/rebuild runs 2-3 hours. Regular braking still works, but no ABS assist. This ties to the NHTSA recalls on ABS system.

Estimated cost: $150-300 per sensor, $500-900 for module

Symptoms: Visible surface rust turning to scale and flaking, Sagging or misaligned body and bed, Cracking around body mount points, Steering or suspension feels loose

Fix: Especially in salt-belt states, the frame rails behind the cab and rear crossmember rust through. Requires frame inspection before purchase. Repair involves cutting and welding sections or full frame replacement. Preventive: fluid film treatment annually, inspect closely at 15+ years old regardless of mileage.

Estimated cost: $2,000-5,000+ depending on severity

Typical onset: 120,000-180,000 mi

Symptoms: Flare or slip on 3-4 upshift, Delayed or harsh engagement into drive, No overdrive or stuck in third gear, Burnt transmission fluid smell

Fix: The 4L60E automatic has a weak 3-4 clutch pack that wears prematurely, especially if fluid changes were neglected. Rebuild required, 8-12 hours labor. Upgraded clutches and shift kit recommended. Keep fluid changed every 50k and install auxiliary trans cooler to extend life.

Estimated cost: $1,800-2,800