This preliminary informational (PI) bulletin provides information to dealership personnel that may be helpful when addressing underbody component corrosion with customers.
full bulletin at NHTSA ↗2020 Chevrolet Blazer powertrain problems
moderate 58 complaints filed with NHTSA · avg repair $2,500 · see powertrain across all vehicles →
Failure mileage
Complaints
58
Recalls
0
Avg fix
$2,500
2injuries
When does it fail?
Of the 58 powertrain complaints filed for the 2020 Chevrolet Blazer, here's the actual mileage breakdown — failures cluster heaviest at 150,000+ mi.
0-25k
25-50k
50-75k
75-100k
100-125k
125-150k
150k+
Each bar shows the share of total complaints filed at that mileage range. Peak failure window highlighted. Some owners report problems earlier; some make it well past 150,000 miles symptom-free. Maintenance habits and driving conditions shift the curve as much as mileage alone.
What stands out
Of the 6 model years of Chevrolet Blazer we track for powertrain problems, this one carries the most owner complaints on file — 58.
Owners have filed 58 powertrain complaints with NHTSA against this vehicle, but no formal recall covers the issue — the federal record reflects what manufacturers have admitted, not everything owners are reporting.
Is there a fix? Manufacturer service bulletins
The manufacturer has issued service bulletins covering powertrain on this vehicle — documented repair instructions, service campaigns, or warranty extensions sent to dealers. A TSB isn't a recall (it's not a free safety remedy), but it's the manufacturer acknowledging the issue and how to fix it.
This bulletin provides information on identifying Non-GM Engine Calibrations for Gasoline Engines using the Tech 2 or GDS 2.
full bulletin at NHTSA ↗This service bulletin provides information on the harmful effects of ethylene glycol in transmission fluid.
full bulletin at NHTSA ↗This service bulletin provides 9th gear operation information to respond to customers that may comment on transmission shift operation.
full bulletin at NHTSA ↗This service bulletin advises the tech that the rotational Clicking Noise Heard After Engine Shut Down may be normal characteristics of the vehicle.
full bulletin at NHTSA ↗Source: NHTSA manufacturer communications. Bring the bulletin number to your dealer or shop.
The failure pattern owners describe
The 2020 Blazer powertrain exhibits a constellation of failures affecting the transmission, engine timing systems, cooling, and electrical control. The shift-to-park sensor is the most frequent complaint—the vehicle does not detect park position, leaving the engine running and preventing shutdown despite the shifter being physically in park. Owners must repeatedly shift between gears to register park, or the warning message persists indefinitely, draining batteries or leaving vehicles unlocked and running. GM issued Technical Service Bulletins (TSB 19-NA-206 and MC-10199243-9999) acknowledging this defect, extended recall coverage to 2021 models, but excluded the 2020 model year, forcing out-of-warranty owners to pay $463 to over $1,000 for shifter assembly replacement.
Transmission failures occur early and catastrophically: one owner reported total failure at 1,500 miles requiring new transmission installation per GM bulletin; another experienced loss of power and stalling at highway speeds. Torque converter failures appear around 82,000 miles with tarnished fluid. Engine timing subsystems fail repeatedly—camshaft actuator solenoids fail twice on single vehicles, sensor replacements recur, and timing chain tensioners spring. Thermostats stick open at 51,000–75,000 miles, causing cooling fans to run continuously and steering assist to reduce. Radiator seals erode or fail internally—one vehicle required three radiator replacements in four years; dealerships confirm this is a known defect but no recall exists. Electrical system faults cause complete power loss, battery drain requiring multiple replacements, and secondary effects like radio lockup and steering controls malfunction. Two owners report vehicles rolling backward after turning off the engine with transmission in drive, resulting in injuries.
Same Chevrolet Blazer powertrain reports on nearby years: 2019 · 2021
Failure modes owners describe
Shift to Park detection failure
The transmission park position sensor or shifter assembly fails to detect that the vehicle is in park, preventing the engine from shutting off and keeping the vehicle in accessory or run mode. The Driver Information Center displays a 'Shift to Park' warning message despite the shifter being physically in park. Owners report the message appearing intermittently or persistently, sometimes requiring multiple attempts to shift into and back out of park before the system registers park. This defect is documented in GM TSB 19-NA-206 and TSB MC-10199243-9999.
When: From 8,000 miles to 128,000 miles, most commonly between 38,000 and 77,000 miles
Symptoms owners cite: Vehicle does not turn off despite shifter in park; 'Shift to Park' warning message displayed when vehicle is already in park; Inability to lock vehicle; Chiming sounds continue as if vehicle is running; Accessory mode activated when park is not recognized; Battery drain from inability to fully power down
Repairs/costs cited: Transmission shifter assembly replacement, transmission control shifter harness replacement, park switch replacement. Repairs reported at $463 to over $1,000 depending on dealership. Some owners report dealers refusing warranty coverage despite issue being known.
Recalls/TSBs owners mention: TSB 19-NA-206 issued; TSB MC-10199243-9999 issued. 2019 models had recall extended; 2020 models excluded from recall. Special coverage available for 2021 models but not 2020. GM has not issued a formal recall for 2020 model year.
Thermostat failure with cooling system malfunction
The thermostat sticks open or fails, causing the cooling fan to run continuously at high speed, the temperature gauge to remain pinned on cold, and reduced air conditioning performance. This failure triggers a 'Steering Assist Reduced' warning message and check engine light. Multiple owners at low mileage report this issue. One owner's research on the Chevy Blazer forum found comments from mechanics stating a faulty wire harness is the underlying cause that dealers do not address, allowing the problem to recur.
When: 51,000 to 75,000 miles, one case at 60,000 miles
Symptoms owners cite: Thermostat sticking open; Cooling fan running continuously at maximum speed; Temperature gauge stuck on cold (C); Reduced or no air conditioning cooling; Check engine light illuminated; 'Steering Assist Reduced Drive with Care' message; Sweet syrup smell (coolant leak odor)
Codes mentioned: P0128
Repairs/costs cited: Thermostat replacement $1,216 to $1,400. One owner questioned why thermostat fails at 75,000 miles on a 5-year-old vehicle and found mechanic forum comments suggesting underlying faulty wire harness causes recurrence. Repairs are not consistent across dealers.
Recalls/TSBs owners mention: Special coverage program issued for 2021 Blazers; not extended to 2020 models. Thermostat repair is the only powertrain warranty coverage offered.
Radiator seal and internal failure
The radiator seal erodes or the radiator fails internally at low mileage. One owner reported complete radiator seal erosion at the upper driver-side area. Multiple owners report three radiator replacements in 4 years on the same vehicle. One owner noted complete internal radiator seal erosion requiring full replacement rather than repair.
When: 53,000 miles; one vehicle required three replacements over 4 years with 64,000 km total
Symptoms owners cite: Internal radiator leakage; Coolant crystallization visible in radiator; Radiator seal eroded or failed; Fluid leaking from front of vehicle
Repairs/costs cited: Full radiator replacement $1,800 at 53,000 miles. One vehicle required three radiators in 4 years. Dealership confirmed this is a widely known defect with this model year.
Recalls/TSBs owners mention: Dealership stated this is a 'very common issue with these cars' and that GM has 'admitted that the seal is bad,' but no recall or service campaign issued. Only thermostat is covered under powertrain warranty.
Camshaft actuator solenoid valve failure
The camshaft actuator solenoid valve fails, triggering variable valve timing (VVT) sensor issues and multiple diagnostic trouble codes. One owner experienced two separate failures at different mileage intervals with different DTC codes each time.
When: 30,000 miles and 60,000 miles (same vehicle, separate incidents)
Symptoms owners cite: Engine hesitation during acceleration; Delays when accelerating; Revving while braking; Sputtering in stop-and-go traffic; Check engine light illuminated
Codes mentioned: P0024 (timing advanced and bouncing around)
Repairs/costs cited: Camshaft actuator solenoid valve replacement performed twice under warranty at Martin Chevrolet. Second failure occurred at 60,000 miles after first replacement at 30,000 miles.
Recalls/TSBs owners mention: Covered under warranty but manufacturer did not escalate to Technical Assistance Center or assign field engineer despite repeated failures, per owner's statement.
Timing chain tensioner spring failure
The timing chain tensioner spring fails, requiring engine re-timing. This is part of the cascade of engine timing system failures reported by one owner.
When: Not specified; occurred as part of series of failures on one vehicle
Symptoms owners cite: Engine timing issues
Repairs/costs cited: Required re-timing of engine; repair details not specified
Camshaft positioning sensor failure
The camshaft positioning sensor fails, preventing proper engine timing control and triggering timing-related diagnostics.
When: Not specified; occurred as part of series of failures on one vehicle
Symptoms owners cite: Timing advanced and bouncing
Codes mentioned: P0024
Repairs/costs cited: Sensor replacement performed
Camshaft carrier case gasket failure with oil leak
The camshaft carrier case gasket develops a major oil leak. One owner reported this failure at 59,000 miles and later found mechanic forum comments indicating this is caused by a faulty wire harness. Another owner was quoted $9,000 to teardown the left side of the engine to address a leaking camshaft carrier gasket.
When: 59,000 miles; quoted repair at unspecified mileage on another vehicle
Symptoms owners cite: Major oil leak from carrier case; 'Steering Assist Reduced' message (may be related electrical effect); Check engine light; Fan running at highest speed
Repairs/costs cited: Requires teardown of left side of engine; one quote $9,000. Mechanic forum commentary suggests underlying wire harness fault.
Torque converter failure
The torque converter fails, causing transmission fluid to become tarnished and dark. One owner reported complete torque converter failure at 82,000 miles with transmission not shifting properly. Another owner had torque converter replaced under warranty but vehicle continues to hesitate and buck on highways.
When: 82,000 miles; one vehicle with replacement around 64,000 km mileage
Symptoms owners cite: Transmission fluid dark or tarnished; Vehicle hesitation during acceleration; Bucking or jerking on highways; Inability to accelerate as intended
Repairs/costs cited: Torque converter replacement confirmed by National Transmission in Long Beach, CA. One replacement covered under warranty; however, vehicle continues to show transmission hesitation after repair.
Transmission shift failure and limp mode
The transmission fails to shift out of first gear or becomes stuck, forcing the vehicle into limp mode. One owner experienced catastrophic transmission failure at 1,500 miles. Another at 80 MPH experienced loss of acceleration and heard abnormal engine sounds, followed by stalling and inability to restart, with 'Shift to Neutral and press the start button' message.
When: 1,500 miles; 40,000 miles on another vehicle; very early failures reported
Symptoms owners cite: RPM spiked with vehicle jolting; Vehicle stuck in first gear; Unable to shift to other gears; Reverse engages as neutral only; Check engine light; Loss of acceleration at highway speed; Vehicle stalling while driving; 'Shift to Neutral and press the start button' message; Vehicle unable to restart
Codes mentioned: Check engine light
Repairs/costs cited: At 1,500 miles, GM dealership informed owner that GM has a technical bulletin requiring technicians not to repair but to install a new transmission. Transmission failure at 40,000 miles confirmed by dealer.
Recalls/TSBs owners mention: GM technical bulletin requires new transmission installation rather than repair.
Vehicle rolling in drive when turned off (park engagement failure)
The vehicle fails to engage park when the transmission is in drive and the engine is shut off. The vehicle then rolls backward or forward, creating an unsafe rollaway hazard. Two owners report injuries from attempting to stop rolling vehicles.
When: Very early in ownership; one at 4,400 miles; one at unknown mileage
Symptoms owners cite: Vehicle rolls backward or forward after engine shut-off; Engine off but transmission not in park
Repairs/costs cited: Root cause not determined by dealers; no repairs documented
Recalls/TSBs owners mention: Dealer offered no assistance; manufacturer not notified in some cases.
Variable Valve Timing (VVT) sensor failure
The variable valve timing sensor fails, triggering check engine light and hesitation. One owner had sensors replaced but the failure recurred, requiring solenoid replacement. Mechanic warned that further recurrence may indicate internal engine failure.
When: 70,000 miles
Symptoms owners cite: Check engine light illuminated; Engine hesitation; Jerking while driving and accelerating
Repairs/costs cited: VVT sensor replaced; failure recurred. Solenoid then replaced and repair held. Mechanic warned that another recurrence might indicate internal engine failure.
Start/Stop accumulator failure
The start/stop accumulator end cap fails, causing hesitation, grinding sounds, and fuel leakage.
When: 157,236 miles
Symptoms owners cite: Vehicle hesitation with grinding sound; Check engine light illuminated; Jerking while driving and accelerating; Fuel leak from front end of vehicle
Repairs/costs cited: Start/stop accumulator end cap replacement needed; not repaired per narrative
DC/DC converter failure causing complete power loss
The DC/DC converter output voltage fails, causing complete loss of electrical power while driving. Vehicle dashboard goes dark and must be restarted. One owner experienced this at a red light with subsequent failure to start, requiring police assistance.
When: Not specified; occurred while stopped at red light
Symptoms owners cite: Complete power loss while driving or at idle; Dashboard goes completely dark; Vehicle cannot restart immediately; Message 'Put vehicle in park and push brake to start' appears after power restoration
Repairs/costs cited: DC/DC converter output voltage malfunction diagnosed
Recalls/TSBs owners mention: Technical bulletin issued but no recall made available.
Engine stalling and loss of power while driving
The engine stalls or loses power while actively driving, including during intersections and highway driving. One owner experienced complete shutdown with locked brakes and steering at an intersection.
When: During operation at various speeds
Symptoms owners cite: Engine stalling while driving; Loss of acceleration; Brakes lock (in one case); Steering wheel locks (in one case); Engine jerking and stalling; Idiot lights flashing; Vehicle feels like it will stall
Repairs/costs cited: One case attributed to faulty P6 module; repair not completed per narrative
Transmission control and shifter electrical system failure
Multiple components in the transmission control and shifter system fail including shifter harness, inline shifter wiring harness jumper, and park switch. The shifter becomes inoperable or the park position is not detected electrically.
When: 20,500 miles to 77,340 miles
Symptoms owners cite: Shift lever becomes inoperable; 'Shift to Park' message displayed; Unable to shift into park
Repairs/costs cited: Transmission control shifter harness, inline shifter wiring harness jumper, and park switch replacements needed; repairs not completed per narratives
Transmission downshift to low gear without warning
The transmission unexpectedly downshifts to low gear without driver input, causing vehicle speed to drop dramatically.
When: Not specified
Symptoms owners cite: Unexpected downshift to low gear; Vehicle speed drops to less than 20 mph; Check engine light illuminated
Repairs/costs cited: Not specified
Battery drain and repeated battery failure
The vehicle experiences premature battery drain and failure. One owner replaced the battery twice in under five years at low mileage. Another owner's battery was completely drained on two separate occasions despite being tested as good at an auto parts store. Battery was then replaced again and drained once more.
When: Not specified; one vehicle required two replacements in five years with 75,000 miles
Symptoms owners cite: Battery completely drained; Vehicle requiring jump-start; Repeated battery drain despite new battery installation
Repairs/costs cited: Battery replacement performed. No electrical diagnostic testing performed at dealership on one vehicle; only code clearing done.
Electrical system malfunction with secondary effects
Electrical system faults trigger various secondary symptoms including audio system lockup, steering column controls malfunction, and phantom radio operation.
When: Not specified
Symptoms owners cite: Radio locked and cannot be controlled; Volume controls inoperable; Steering column pedal controls inoperable; Radio continues to play after car is shut off before cutting off
Codes mentioned: P6 module fault (unconfirmed)
Repairs/costs cited: Faulty P6 suspected per dealership; no repairs completed per narrative
Transmission slip under load
The transmission slips during acceleration or under load, causing significant loss of motive power and high risk of accident. One owner experienced transmission slip in active highway traffic before subsequent catastrophic failure at dealership lot.
When: Before final failure; mileage not specified
Symptoms owners cite: Transmission slips during acceleration; Significant loss of motive power; High risk of rear-end collision; Preceded complete transmission failure
Repairs/costs cited: Owner states 'check ball' metallurgical defect caused failure; vehicle became inoperable
Transmission reverse engagement failure
The transmission fails to respond when shifted into reverse, or reverse engages as neutral only without providing reverse motion.
When: 40,000 miles
Symptoms owners cite: Vehicle does not engage reverse; Reverse acts as neutral
Repairs/costs cited: Not repaired per narrative
Camshaft timing over-advanced fault
The variable valve timing system detects camshaft timing that is over-advanced, triggering diagnostic code. One owner reported this code occurred three times before dealer service.
When: Not specified; occurred multiple times before diagnosis
Symptoms owners cite: Check engine light illuminated
Codes mentioned: P0021 - A camshaft position timing over-advanced Bank 2
Repairs/costs cited: Repair covered under powertrain warranty per dealer agreement
Recalls/TSBs owners mention: Covered under powertrain warranty
Synthesized from 58 NHTSA owner complaints — unverified consumer allegations, summarized for patterns. The verbatim filings appear below.
What owners are reporting 5 most recent
The contact owns a 2020 Chevrolet Blazer. The contact stated that while driving at an undisclosed speed, the vehicle hesitated with a grinding sound coming from the vehicle, with the check engine warning light illuminated. The contact stated that the vehicle was jerking while driving and while accelerating from a stop. In addition, the contact noticed fuel leaking from the front end of the…
The vehicle drops to low gear without warning (check engine light comes on). Causing speed to drop to less than 20Mph max.
I pulled in my driveway which is on a slight incline. I turned the vehicle off but the transmission was still in drive. Not realizing this I stepped out of the vehicle and the vehicle started rolling back down my driveway across the sidewalk and into the street. Had there been anyone walking on the sidewalk the vehicle would have hit them or there could have been an accident in the street. I…
Steering assist reduced message followed by check engine light came on and temperature gauge not moving from cold. Immediately took it to the dealership Hiley Chevrolet in Rockwall, TX. After $250 for diagnostic, failed thermostat is the cause and $1216 repair cost. Known issue that Chevrolet issued special coverage for 2021 Blazers, but none for 2020. My vehicle has a little more than 51,970…
P0128 code- Assisted steering fault Check engine light Ac blowing cold Temp gauge flat lined Need to replace temp sensor and thermostat. Others with this issue have reported steering can completely lock up, which could cause serious accidents which could result in fatalities.
Had powertrain trouble with your 2020 Chevrolet Blazer?
File a complaint with NHTSA → It's free, official, and how every report above got here — owner filings are the federal safety record this page is built on.
Common questions
How serious is the powertrain problem on the 2020 Chevrolet Blazer?
It's a documented issue but not catastrophic. 58 complaints have been filed. Repairs average $2,500 and most owners catch it before it causes a breakdown.
At what mileage does the powertrain typically fail?
Across the 14 complaints that reported odometer mileage, most powertrain failures cluster between 20,500 and 70,000 miles, with the median around 50,000. A quarter of owners report trouble before 20,500; a quarter make it past 70,000. Maintenance history matters more than the odometer alone — this is the reported failure window, not a guarantee.
What does it cost to fix?
Independent shops typically charge around $2,500 for powertrain repairs on this vehicle. Dealer pricing tends to run 20-40% higher. The exact figure depends on the specific failure mode, parts availability, and your local labor rates. If you're outside factory warranty, an extended service contract often covers this category.
Are there any recalls related to powertrain?
No active recalls currently cover powertrain issues on this vehicle. The complaints filed represent owner-reported failures that haven't risen to the level of a manufacturer-issued recall — but they're still worth knowing about before you buy or budget for repairs.
Related
Complaint and recall data sourced from the National Highway Traffic Safety Administration (NHTSA)
public records database. Verify the raw federal record at
nhtsa.gov/vehicle/2020/Chevrolet/Blazer.
Severity ratings are derived from reported crashes, fires, injuries, and fatalities. Repair cost estimates are
independent-shop national averages and may differ in your area. Some links on this page are affiliate links.