The 2021 Blazer shares its platform with GM's 9-speed automatic transmission, which has been problematic across multiple brands. The 2.0L turbo shows early low-speed pre-ignition (LSPI) issues leading to catastrophic engine damage, while the 3.6L V6 is generally more reliable but not immune to transmission gremlins.
2.0L Turbo Catastrophic Engine Failure (LSPI)
Occasional · high severityTypical onset: 20,000-60,000 mi
Symptoms: Sudden loss of power with metallic knocking, Check engine light with misfire codes, Oil consumption before failure, Metal shavings in oil during regular changes
Fix: Low-speed pre-ignition destroys pistons and rods. Requires complete engine replacement or short block. 18-24 labor hours for R&R. GM has extended some warranties but many owners pay out of pocket.
Estimated cost: $8,000-12,000
9-Speed Transmission Shudder and Slipping
Common · medium severityTypical onset: 30,000-80,000 mi
Symptoms: Harsh shifts between 2nd and 3rd gear, Shudder or vibration during light acceleration 25-45 mph, Delayed engagement when shifting to Drive or Reverse, Transmission overheating warnings
Fix: TSBs call for fluid flushes with updated fluid, torque converter replacement, or complete valve body replacement. Flush takes 2 hours, torque converter 8-10 hours, valve body 12-14 hours. Multiple attempts common before resolution.
Estimated cost: $400-4,500
Transmission Oil Cooler Line Leaks
Common · medium severityTypical onset: 40,000-90,000 mi
Symptoms: Transmission fluid puddles under vehicle, Burnt transmission fluid smell, Low fluid level warnings, Lines corrode at crimp fittings near radiator
Fix: Hard lines corrode where they connect to cooler. Requires replacement of affected lines and fittings. 3-4 labor hours including fluid refill and system check.
Estimated cost: $600-1,200
Transmission Mount Failure
Occasional · low severityTypical onset: 50,000-100,000 mi
Symptoms: Clunk when shifting from Park to Drive, Excessive vibration at idle in gear, Visible engine movement during acceleration, Rubber mount separation visible on inspection
Fix: Hydraulic transmission mount fails prematurely. Replacement requires supporting powertrain. 2-3 labor hours.
Estimated cost: $400-700
Electronic Throttle Control Failures
Occasional · high severitySymptoms: Reduced engine power warning, Vehicle enters limp mode unexpectedly, Throttle response lag or complete loss, P2138 throttle position sensor correlation codes
Fix: Throttle body or accelerator pedal position sensor fails. Diagnosis 1 hour, throttle body replacement 1.5 hours, pedal assembly 1 hour. May require both components.
Estimated cost: $500-1,400
Fuel Pump Module Failures
Rare · high severityTypical onset: 60,000-120,000 mi
Symptoms: No-start condition with full tank, Engine stalling during acceleration, Fuel pressure fluctuations, Whining noise from fuel tank area
Fix: In-tank fuel pump module fails. Requires dropping fuel tank or removing rear seat for access depending on configuration. 4-5 labor hours.
Estimated cost: $900-1,600
The 3.6L V6 is the safer bet; avoid the 2.0L turbo unless you have comprehensive warranty coverage and documented oil analysis history showing clean engine internals.
AI-assisted summary drawn from NHTSA recall data, our labor-times database, and platform knowledge. Not a substitute for a pre-purchase inspection on a specific vehicle.