2021 GMC Sierra powertrain problems

Broken rocker arms, failed lifters, and damaged push rods causing sudden misfiring, knocking, rough idle, and loss of engine power. Failures occur across both 5.3L and 6.2L V8 engines and have recurred in some vehicles after repair.

When: Between 8,464 and 97,000 miles; some vehicles experience recurrence after initial repair

Symptoms owners cite: Loud knocking or ticking noise from engine; Rough idle; Loss of power and hesitation; Check engine light and warning lamps; Metal shavings in oil; Engine misfiring, particularly in specific cylinders

Codes mentioned: P0303, Check engine light with lifter/valvetrain diagnosis

Repairs/costs cited: Lifter replacement (8 to 16 units), camshaft replacement, engine rebuild or full engine replacement. Parts shortage reported. Costs cited range from $6,000 to $12,000+; some covered under warranty but warranties have limits and exclusions.

Recalls/TSBs owners mention: GM issued service bulletin for lifter replacement on pre-delivery vehicles (early December 2021). Some repairs covered under powertrain warranty; extended warranty denied in at least one documented case. No recall issued for lifter failures in general.

Transmission control valve and valve body failures causing loss of motive power, hard shifting, jerking, shuddering, reduced engine power mode, and limp mode. Some vehicles fail multiple times despite repair or software updates.

When: 27,676 to 119,000 miles; failures occurring shortly after dealership repair are reported

Symptoms owners cite: Loss of motive power or inability to accelerate beyond 4-10 mph; Hard jerking and shifting; Shuddering at specific speed ranges (35–45 mph, 65–75 mph, around 1,200 RPM); Reduced engine power message; Limp mode activation; Check engine light; Transmission hesitation on initial shifts

Codes mentioned: P1098, Transmission error codes (multiple, owner-reported)

Repairs/costs cited: Transmission valve body or transmission control valve replacement. Metal shavings found inside transmission in at least one case. Parts on national backorder; repairs delayed 30–120 days or longer. Costs $1,200–$6,500+ for replacement; full transmission replacement cited at $6,000–$7,000. Some covers under powertrain warranty (100,000 mile coverage for diesel models) but interpretation disputed.

Recalls/TSBs owners mention: NHTSA Recall 24V797000 issued for certain 2020–2022 diesel-equipped models (and some gas models). Interim and permanent repairs available, but complaints indicate failures continue after permanent repair completion. GM stated coolant control valve not covered under powertrain warranty in some cases, contradicting owner expectations. Extended warranty (up to 15 years/150k miles) issued September 2025 but some owners' VINs excluded without explanation.

Premature failure of engine coolant control valve in 3.0L Duramax diesel engines causing check engine light, reduced engine power mode, excessive fan operation, and rapid overheating risk.

When: 60,000 miles reported; failures beginning mid-2024 to early 2025

Symptoms owners cite: Check engine light illumination; Reduced engine power message; Coolant fans running at 100% continuously; Excessive fan noise; Potential rapid engine overheating; Vehicle speed limiting on freeway (hazardous during towing)

Codes mentioned: P1098

Repairs/costs cited: Coolant control valve replacement required. Replacement part on nationwide backorder for 30–120 days. Some dealers report repair not covered under 100,000-mile powertrain warranty, though customers dispute this. ECM reprogramming sometimes required as first step (one owner charged $195, not covered under warranty). Costs in thousands of dollars.

Recalls/TSBs owners mention: No recall issued for coolant control valve failure. GM issued special extended warranty (September 2025) for 15 years/150,000 miles but some VINs excluded without clear criteria. No service bulletin identified in narratives. Widespread backorder of parts suggests known systemic issue.

Excessive wear in transmission control valve causing rear wheel lock-up during braking, downshifting, or normal highway driving. Related to NHTSA Recall 24V797000 (some models).

When: 29,000 to 119,000 miles; incidents occurring after temporary and permanent recall repairs

Symptoms owners cite: Unexpected rear wheel lock-up during downshifting or braking; Parking brake warning light flashing; Vehicle deceleration without driver input (70 mph to 50 mph or below); Speed limiting to 50 mph or less on highway; No warning or fault codes initially; codes appear later if checked

Codes mentioned: Recall 24V797000, Recall N242454440

Repairs/costs cited: Interim software update installed but did not prevent recurrence. Permanent transmission valve replacement required; metal shavings found in transmission fluid in at least one case. Repair delayed or incomplete in multiple cases. Owner quoted that dealer stated valve would 'fail again.'

Recalls/TSBs owners mention: NHTSA Recall 24V797000 (Power Train) and N242454440 issued. Interim repair (software) provided; permanent repair (valve replacement) deployed starting March 2025 but complaints indicate failures continue post-repair. GM response characterized as evasive; software fix viewed by owners as liability-limiting rather than safety-fixing.

Excessive oil consumption and burning from engine despite normal operation, requiring frequent oil top-ups between scheduled changes.

When: Early ownership; manifests 3,000+ miles into ownership; increases with age

Symptoms owners cite: Low oil warning messages before scheduled oil changes; Oil not registering on dipstick; Burning smell reported in some cases; White smoke from exhaust on acceleration (some cases)

Codes mentioned: Check engine light (in some cases), Catalytic converter fault codes (in some cases, possibly secondary)

Repairs/costs cited: No repair offered; dealership service advisors indicate this is normal for the model. Average consumption cited at 2.5 quarts per 7,500-mile oil change interval, well above industry norms. One owner added up to 3 quarts between oil changes.

Recalls/TSBs owners mention: No recall or service bulletin identified. Dealership response is to perform oil changes and dismiss complaints as normal; no investigation conducted in narratives reviewed.

Complete engine seizure or major internal failure requiring full engine replacement, often without prior warning. Failures include seized bearings, bent camshafts, and internal damage. One case involved engine failing only 1,585 miles after purchase.

When: Under 5 days to 97,000 miles after purchase or during ownership

Symptoms owners cite: Sudden loss of power at highway speed; No warning prior to failure; Metal shavings in oil (in some cases); Loud bang or knocking from engine compartment; Possible brief check engine light before catastrophic failure

Codes mentioned: Diagnostic codes vary; one case involved 'seized bearing' diagnosis without specific code cited

Repairs/costs cited: Full engine replacement required. Costs not specified in most narratives but implied to be $6,000+. One dealership initial misdiagnosis (replaced starter for $1,200 before identifying actual engine defect). Engine replacement may take 3–25 days to complete; in one case, replacement engine arrived with unknown origin (remanufactured vs. new unclear) and came with reduced or no additional warranty (7,000 miles cited).

Recalls/TSBs owners mention: One narrative indicates dealership 'knowingly sold' defective 6.2L V8 engine and that defect was 'under investigation by NHTSA'; however, no formal recall or TSB identified for general catastrophic engine failure. GM warranty covers some engine replacements but conditions and exclusions apply.

Defective diesel exhaust fluid (DEF) tank failure occurring multiple times on same vehicle, with replacement part on nationwide backorder.

When: Within 14-month ownership window; second failure occurs after first replacement

Symptoms owners cite: DEF tank malfunction or failure requiring replacement

Repairs/costs cited: Tank replacement required. Part on nationwide backorder with 30+ day wait; dealers unable to provide ETA. Owners report multiple trucks at different dealerships waiting on same part. Cost not specified; vehicle unavailable for extended period (2+ months reported).

Recalls/TSBs owners mention: No recall issued. Dealership confirms nationwide issue. No warranty coverage or loaner vehicle offered by dealership in at least one case; customer made payments on unusable vehicle.

Hard shifting, delayed shifts, shuddering, hesitation, and erratic transmission behavior at various speeds and driving conditions. Issues may persist or worsen over time and sometimes follow dealership service.

When: Early ownership (as low as 8,000 miles), continuing to 120,000+ miles

Symptoms owners cite: Hard or jerky shifting between gears; Shuddering at specific speeds (35–45 mph, 65–75 mph ranges); Hesitation during acceleration or uphill driving; Transmission bouncing or bouncy shifting, particularly downshifting; Low RPM shuddering (around 1,200 RPM); Issues worse during stops or low-speed acceleration

Codes mentioned: No warning lamps or codes in some cases; others cite check engine light and transmission error codes

Repairs/costs cited: Transmission fluid flushes and valve body replacements attempted; issues recur. Transmission valve body replacement with zero ETA on parts. One owner quoted $6,200–$6,500 for transmission replacement with no rebuilding available.

Recalls/TSBs owners mention: TSB 16-NA-361 referenced in one case; manufacturer had not made repair available as of complaint filing. Interim software updates attempted on some vehicles (recall-related) but shuddering and shifting issues persist.

Transmission failure to upshift to higher gears, resulting in vehicle limited to 40–50 mph on highways during normal driving or while towing. Occurs after software updates and recall repairs.

When: 90,000+ miles; post-recall service

Symptoms owners cite: Transmission stuck in lower gears; Vehicle unable to exceed 40–50 mph even with accelerator fully depressed; Loss of power or acceleration capability on highway; Limp mode activation; Occurs under normal driving and towing conditions

Codes mentioned: P0303 and others (codes cited vary)

Repairs/costs cited: Valve replacement required; parts on backorder. Software update (recall-related) did not fix underlying mechanical issue; interpreted by owners as intentional 'limp mode' to avoid transmission failure rather than true repair.

Recalls/TSBs owners mention: Recall 24V797000 software patch deployed but characterized by owners as inadequate; permanent valve replacement remedy developed but parts scarce.

Persistent rough idle at stops and low speeds, sometimes accompanied by hesitation during acceleration. In some cases, follows dealership service or filters change.

When: Early ownership and continuing; one case immediately after dealership filter service

Repairs/costs cited: No repairs documented. Dealership diagnostics performed without resolution in some cases. One owner suspects ECM or sensor reprogramming may be required.

Recalls/TSBs owners mention: No service bulletin or recall identified.

Transmission cable or shift linkage failure resulting in inability to shift vehicle or vehicle stalling.

When: Early ownership (3,000 miles reported)

Symptoms owners cite: Vehicle stalls at low or undisclosed speeds; Difficulty or inability to shift transmission properly; Recurring stall after repair attempts

Repairs/costs cited: Cable replacement attempted but failure recurred; root cause not definitively identified across three different dealership attempts.

Recalls/TSBs owners mention: Vehicle passed through three dealers with conflicting diagnoses (battery, transmission cable, unknown). No definitive repair located.

Faulty fuel pump failure resulting in loss of propulsion and limp mode while towing. Related to a recall on other GM models but not applied to affected vehicle.

When: Undisclosed mileage; fuel pump failure requiring replacement; previous sensor issues reported throughout ownership

Symptoms owners cite: Inability to accelerate despite engine running; No fault codes or warnings initially; Reduced engine power mode activation; Diesel smell reported; Vehicle stalls or loses power

Repairs/costs cited: Fuel pump replacement required; estimated cost $1,000, not covered under powertrain warranty per dealership. Part not available immediately.

Recalls/TSBs owners mention: Recall issued on other GMC models for fuel pump; not extended to vehicle in question despite identical failure and safety risk. Owner reports multiple sensor replacements under warranty during ownership, but fuel pump excluded.

Repeated check engine light illumination with various diagnostic codes (catalytic converter, NOX catalyst, coolant valve, fuel system) that are not resolved or recur shortly after service.

When: Throughout ownership; some resolved, others recur within days to weeks

Symptoms owners cite: Check engine light illumination; Reduced engine power message; Erratic drivability depending on code

Codes mentioned: P1098 (coolant control valve), NOX catalyst below threshold, Catalytic converter faults, Fuel injector codes, Transmission codes

Repairs/costs cited: Fuel tank cleaning, fuel treatment, transmission fluid replacement, valve replacements attempted. Catalytic converter replacement cost disputed; owner questions whether catalytic converter is root cause or secondary failure from oil burning.

Recalls/TSBs owners mention: No comprehensive service bulletin addressing pattern of multiple code recurrence. Dealership responses fragmented across different issues.

Sudden loss of engine power, limp mode activation, or severe deceleration while driving on highway at speed, creating hazardous situations.

When: Throughout ownership at various mileages, often without warning

Symptoms owners cite: Loss of acceleration or power; Engine power reduced message; Limp mode activation; Deceleration from 70 mph to 50 mph or below without driver input; Vehicle unable to maintain highway speeds

Codes mentioned: Multiple transmission, engine, and sensor-related codes

Repairs/costs cited: Repairs vary by underlying cause (coolant valve, transmission valve, sensor, fuel pump, etc.). Multiple repair attempts in some cases; root cause may be masked by symptoms.

Recalls/TSBs owners mention: Recall 24V797000 and others address some instances; however, owner reports indicate fixes are incomplete and problems recur.