GMC Sierra 1500 T1XX

3.0L inline-6 diesel, aluminum block, single turbo — the only I6 diesel in a US half-ton. LM2 (2020-2022): crankshaft reluctor wheel fails, engine cranks without starting. Repair requires cab-off, 40+ labor hours. LZ0 (2023+) got steel pistons, revised turbo, 305 hp / 495 lb-ft. Oil pump sits at rear of the block: transmission-out job for a $30 part. Highway 26-28 mpg empty, 12-14 mpg towing.

• !! Engine Cranks Without Starting (LM2 2020-2022) from 30,000 km

  Crankshaft reluctor wheel fails — engine cranks without starting. Repair requires cab removal (40h labor).

  Symptoms: Engine cranks without starting, especially cold, intermittent
  3,000–8,000 $
  Ad LM2 camshaft trigger wheel P0341 Duramax 3.0PIP5806 TSB LM2 no start
• !! Rear Main Seal Leak from 50,000 km

  Seal leaks on early LM2 (2020-2022). Oil spots under the vehicle.

  Symptoms: Oil spots under vehicle, dropping oil level
  800–2,500 $
  Ad 40009072 GM rear main seal 3.0 Duramax LM255506777 GM rear main seal LM2
• !! DEF System Failure from 60,000 km

  "Service DEF System" warning, limp mode, no-start in extreme cases. Injector, sensor or pump defective.

  Symptoms: Service DEF warning, power reduction, limp mode
  500–3,000 $
  Ad LM2 DEF SCR dosing injector 3.0 Duramax40009195 LM2 Duramax injector

5.3L V8, iron block, the most-produced truck engine in North America. DFM shuts down up to 15 of 16 firing patterns — and that's the problem. Lifter needle bearings starve for oil in deactivated cylinders, skid across cam lobes, send metal through the engine. Two class actions pending. A $200 Range disabler buys time; a $2,500 mechanical delete with DOD-delete cam is the permanent fix. Run 0W-20 Dexos, change at 5,000 miles maximum.

• !! AFM/DFM Lifter Failure — Class Action from 100,000 km

  THE GM truck problem: deactivated cylinder lifters wear from oil starvation. Needle bearing skids on cam lobe, metal debris in oil. Two class actions pending. $3,500-8,500 repair. AFM/DFM delete kit as permanent fix.

  Symptoms: Loud ticking/knocking, misfires, rough running, check engine, sometimes from just 25k miles
  3,500–8,500 $
  Ad 12698946 AFM lifter valve assembly L8412645725 AFM lifter GM 5.3L12723516 DFM camshaft repair kit L84DFM lifter delete kit 5.3 EcoTec3
• !! Oil Consumption — Piston Rings (Class Action) from 80,000 km

  Separate class action: $150M settlement for 2011-2021. Piston rings let oil pass — 1 quart per 2,000 miles in severe cases.

  Symptoms: Blue smoke, dropping oil level, fouled spark plugs
  2,000–6,000 $
  Ad 12698946 AFM lifter L84 5.3LHastings 2M5380 piston ring set Gen V 5.3L
• !! Timing Chain Wear from 160,000 km

  Same issue as LV3 — chain and guides from ~100k miles.

  Symptoms: Cold start rattle, P0008/P0016
  1,000–2,500 $
  Ad 12630107 timing chain tensioner Gen V LT12680750 timing chain kit 5.3L EcoTec312713934 crankshaft sprocket gear Gen V

6.2L V8, 420 hp, same Gen V architecture as the 5.3 but deeper exhaust note and noticeably more shove. 2021-2024: manufacturing left metal shavings in 597,000 engines — GM's fix was switching to 0W-40 oil. NHTSA opened an investigation into post-recall failures. Same DFM lifter risk as the 5.3. Pre-2021 or confirmed post-recall units with documented oil changes are the buy.

• !! Recall: Metal Shavings in Engine — 597,000 Vehicles

  Manufacturing debris (metal shavings) in engine destroys bearings. 2021-2024 L87. Free engine replacement, 6-8 week wait. NHTSA investigating post-recall failures.

  0–0 $
  Ad L87 engine recall 25V274 replacement engineGM safety recall N252494001 L87
• !! AFM/DFM Lifter Failure from 100,000 km

  Same lifter issue as 5.3L — cylinder deactivation wears lifters.

  Symptoms: Ticking/knocking, misfires, rough running
  3,500–8,500 $
  Ad 12688943 GM MLS head gasket 6.2 L87L87 DFM delete kit 6.2 Gen V
• !! Oil Consumption — Piston Rings (2019-2020 and older L87) from 80,000 km

  Piston rings let oil past — 0.5-1 quart per 2,000 miles in severe cases. Also affects 2019-2020 L87 not covered by the machining debris recall. NHTSA investigating these cases separately.

  Symptoms: Blue smoke, dropping oil level, fouled spark plugs, positive oil consumption test
  2,500–7,000 $
  Ad piston rings GM 5.3 L84oil consumption fix Silverado

+ 1 more engine weaknesses + vehicle weaknesses

2.7L turbo four, aluminum block, direct injection only — GM's answer to Ford's EcoBoost. 310 hp, 400 lb-ft from 1,500 rpm. Feels like a small V8 until the revs climb and the four-cylinder character shows. Head gasket failures on 2019-2022 early production under 25k miles, warranty-covered. A fleet of 750+ trucks at 50-80k miles with zero engine failures suggests the 2022+ builds are sorted.

• !! Head Gasket on Early Models (2019-2022) from 30,000 km

  Head gasket fails on early L3B under 25k miles. Covered under warranty.

  Symptoms: White smoke, overheating, milky oil
  1,500–4,000 $
  Ad head gasket L3B 2.7 turbo Silveradooil cooler block gasket L3B 2.7
• !! Turbo Bearing Wear from 80,000 km

  Poor oil quality or extended intervals destroy turbo bearings.

  Symptoms: Turbo lag, whine, blue smoke, power loss
  1,500–4,000 $
  Ad 12701386 turbocharger assembly L3B 2.7T12716475 wastegate actuator L3B
• !! Injector failure (ECM update available 2019-2022) from 80,000 km

  Fuel injectors wear or fail — incorrect ECM programming (2019-2022) causes wrong injection quantity. Service Update N242450631 available as free fix.

  Symptoms: Rough idle, misfires, poor fuel economy, check engine light
  300–600 $
  Ad 12688000 high pressure fuel pump L3B 2.7THPFP direct injection pump Silverado 2.7

+ 2 more engine weaknesses + vehicle weaknesses