This message concerns a persistent engine light that activates and generates engine code P0299, indicating an engine underboost issue. There have been several occasions where I am driving over 55mph on the highway and my 2020 Terrain SLT fails to pick up speed over 60mph in traffic. I took it to my GMC dealer earlier this year for them to diagnose, and they discovered that the charge air cooler…
2020 GMC Terrain engine problems
moderate 17 complaints filed with NHTSA · avg repair $3,100 · see engine across all vehicles →
Complaints
17
Recalls
0
Avg fix
$3,100
The failure pattern owners describe
Buyer takeaway: A 2020 GMC Terrain can experience sudden engine power loss, internal engine damage, or complete engine failure with little to no warning across its lifespan. Owners report multiple catastrophic failures—including those already repaired once—that GMC has not recalled despite identified defects in fuel pumps, vacuum pumps, and turbocharger systems.
Owners report catastrophic engine failures across a range of mileages (24k to 71k miles) with the 2020 GMC Terrain engine. Most frequent complaint is sudden loss of engine power while driving—vehicle either shuts down completely or becomes unresponsive and must coast to safety. In many cases, no warning lights appear before failure, leaving drivers without diagnostic opportunity. Once power is lost, engines often will not restart or require multiple attempts.
When engines are inspected, dealers find internal damage: metal shavings in oil, seized engines, detached camshaft end caps, and broken crankshafts. Root causes cited include failed vacuum pumps (which shear camshafts and skip timing), fuel pump module failures (with recurrence after replacement), turbocharger issues causing underboost conditions, and throttle body malfunctions. Several owners report fuel pump module failures that recurred even after replacement, questioning whether recalled parts are being installed.
Power-loss complaints often happen during critical driving situations—entering traffic, highway merging, intersections—creating serious safety hazard. One owner's daughter nearly got t-boned. Another owner's vehicle engaged its own park setting while driving at highway speed. Multiple owners state engines require full replacement but GMC denied warranty coverage or quoted repair costs exceeding $15,000 despite vehicles being under warranty or having low mileage. Dealers have been unable to diagnose intermittent power-loss events because diagnostic codes do not appear on demand.
Same GMC Terrain engine reports on nearby years: 2017 · 2018 · 2019
Failure modes owners describe
Sudden engine loss of power/engine shut-off while driving
Engine loses motive power unexpectedly while driving at highway or moderate speeds, sometimes without warning lights. Vehicle shuts down completely or loses all power and fails to restart on first attempt. Creates immediate hazard as driver must coast to safety.
When: Various mileages reported: 50k, 67k, 48.5k, unknown; some incidents recurred multiple times
Symptoms owners cite: Complete loss of engine power while driving; Engine will not restart or requires multiple restart attempts; No warning lights before failure in some cases; Check engine light may illuminate after the event; Vehicle forced to coast to shoulder or safe location
Codes mentioned: P0299 (engine underboost)
Repairs/costs cited: One report mentions fuel pump module replaced twice ($591 first repair, second covered under warranty after first failure at ~50k miles). Multiple reports indicate full engine replacement needed but some owners unable to afford repair or warranty not honored.
Recalls/TSBs owners mention: Recall exists for 2021-2022 Chevrolet Equinox and 2022 GMC Terrain fuel pump module (2020 model year not explicitly listed). Case opened per NHTSA Campaign 25V274000 for some reports; manufacturer referred owners to dealership or NHTSA Hotline, offered no assistance in other cases.
Engine internal damage (metal shavings, seized engine, camshaft failure, broken crankshaft)
Catastrophic internal engine damage including metal shavings in oil, seized engines, detached camshaft end caps, skipped timing from camshaft damage, and broken crankshafts. Occurs without prior warning in most cases. Engine requires complete replacement.
When: Reported at 67k, 48.5k, 71k, 24.2k, and unknown mileages; some with fewer than 4 years age
Symptoms owners cite: No prior warning signs in most cases; Engine loss of power; Flashing or solid check engine light (may appear after failure); Vehicle shaking while driving; Inability to accelerate under load; Metal debris found in engine during inspection
Repairs/costs cited: Full engine replacement required in all cases. One owner cited repair cost estimate over $15,000. Dealers disassembled engines in some cases but were unable to repair; vehicles not repaired or owners unable to afford replacement.
Recalls/TSBs owners mention: No recall associated with some VINs per manufacturer statement. Manufacturer offered no assistance in most cases. Some owners referred to NHTSA for investigation.
Vacuum pump failure / camshaft reluctor failure
Vacuum pump shatters or locks up, causing loss of brake assist and motive power. GMC engineer identified camshaft reluctor as root cause in one case. Vacuum pump failure can shear off camshaft end or cause timing skip.
When: ~50k miles and 71k miles reported
Symptoms owners cite: Loss of braking power; Loss of engine motive power; Brake pedal goes to floorboard; Grinding sounds from engine while driving; No warning lights illuminated before failure
Repairs/costs cited: Vacuum pump replaced (failed again); GMC engineer attributed failure to camshaft reluctor. In one case, multiple components replaced (vacuum pump, exhaust camshaft, valve cover gasket) but engine then lost power, requiring full engine replacement.
Recalls/TSBs owners mention: GMC engineer was contacted in one case and diagnosed camshaft reluctor as the failure cause.
Turbocharger / air intake system failures
Recurring underboost condition due to moisture in charge air cooler tube, turbo wastegate actuator failure, and mass air flow sensor issues. Engine underboost code appears repeatedly; problem resurfaces after repair, especially in cold weather.
When: Reported at 38k and 50k+ mileage; recurring issue after ~1 month of repair in cold weather
Symptoms owners cite: Check engine light with P0299 (underboost) code; Reduced engine power message displayed; Vehicle cannot exceed 55-60 mph on highway; Loss of power/acceleration capability; Blue smoke from exhaust (one report); Intermittent symptoms that may resolve after days of driving
Codes mentioned: P0299 (engine underboost)
Repairs/costs cited: Charge air cooler tube cleared of moisture; turbo wastegate actuator replaced; air pipe charge and air cooler replaced; throttle body replaced; mass air flow sensor replaced; software update performed. Problem recurred in multiple cases despite repairs.
Recalls/TSBs owners mention: Manufacturer referred to local dealers. One case involved Power GMC Chevrolet of Newport, OR.
Throttle body / electronic throttle failure
Vehicle loses engine power due to throttle failure or throttle body malfunction. Engine power cuts without warning and vehicle refuses to accelerate despite pressing gas pedal. RPMs do not respond.
When: 38k miles mentioned; incidents recur intermittently
Symptoms owners cite: Vehicle will not accelerate from complete stop or while driving; Gas pedal pressed but vehicle does not respond; No engine codes thrown (in some cases); No power / transmission slipping feeling; RPMs unresponsive; Intermittent events that cannot be consistently reproduced for diagnostics
Repairs/costs cited: Throttle body replaced; failed again. Throttle identified as failed component in another case.
Fuel pump module failure
Engine shuts off suddenly while driving without warning. Occurs in traffic or during highway driving, creating hazard. Failure recurred after initial fuel pump module replacement.
When: First failure March 2022, second failure May 2023; vehicle at 24.2k miles noted in one case
Symptoms owners cite: Engine cuts off while driving; No warning lights or messages before failure; Complete engine shutdown; Vehicle must be restarted
Repairs/costs cited: Fuel pump module replaced in March 2022 for $591; replaced again in May 2023 at no charge (dealer claimed second module was faulty). One owner questions whether recall part was used in second repair.
Recalls/TSBs owners mention: GMC recall exists for 2021-2022 Chevrolet Equinox and 2022 GMC Terrain fuel pump module; 2020 model year not explicitly listed in recall notice per owner.
Oil loss / low oil engine damage
Engine loses oil due to internal defect, causing engine damage. Owner reports no early warning lights of low oil condition despite maintenance at dealership.
When: 24.2k miles when warning lights appeared
Symptoms owners cite: Warning lights appear indicating low oil / engine issue; Loss of oil; Engine failure requiring replacement
Repairs/costs cited: Owner reports GMC dealership improperly serviced vehicle when brought in with warning lights (September 2021). Same warning lights reappeared October 2021. New engine required (not installed; cost quoted over $15,000).
Recalls/TSBs owners mention: Vehicle under new car warranty but GMC requested owner pay over $15,000 for engine replacement and installation despite being under warranty.
Intermittent loss of power / hesitation on acceleration
Vehicle hesitates or refuses to accelerate when pressing gas pedal, especially at traffic lights or when pulling into traffic. Power loss is intermittent and difficult to diagnose. Creates safety hazard when attempting to enter traffic.
When: 38k miles mentioned; multiple intermittent incidents reported
Symptoms owners cite: Vehicle will not accelerate from stop despite gas pedal input; Hesitation when taking off from red light; Loss of power when pulling into traffic or reversing; No diagnostic codes visible to technician; Events recur randomly but cannot be reproduced on demand; Sensation of transmission slipping or power loss
Repairs/costs cited: No repairs documented as codes not present when vehicle brought to dealer. One mechanic suggested trading vehicle in.
Brake system failure / loss of braking power
Brake pedal loses pressure or goes to floorboard while depressed. Vehicle fails to stop as expected. No warning lights in some cases.
When: Various incidents; 31k miles mentioned in one case
Symptoms owners cite: Brake pedal loses resistance or goes to floorboard; Vehicle does not stop / braking power lost; No warning lights illuminated; Vehicle locks up or brakes engage unexpectedly (uncontrolled emergency braking)
Repairs/costs cited: Vacuum pump, exhaust camshaft, and valve cover gasket replaced in one case, but engine then lost motive power requiring full engine replacement.
Recalls/TSBs owners mention: OnStar diagnostic indicated on-star safety feature malfunction in one case; no recall noted for brake issues.
Synthesized from 17 NHTSA owner complaints — unverified consumer allegations, summarized for patterns. The verbatim filings appear below.
What owners are reporting 1 most recent
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Common questions
How serious is the engine problem on the 2020 GMC Terrain?
It's a documented issue but not catastrophic. 17 complaints have been filed. Repairs average $3,100 and most owners catch it before it causes a breakdown.
At what mileage does the engine typically fail?
Based on the 17 complaints filed, engine issues most often appear around 55,184 miles. Some report problems earlier; some make it well past 150,000 with no symptoms. Maintenance habits matter — vehicles that received timely fluid services and were not regularly overworked tend to last longer.
What does it cost to fix?
Independent shops typically charge around $3,100 for engine 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 engine?
No active recalls currently cover engine 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/GMC/Terrain.
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.