I purchased this 2018 GMC pickup in May 2021. Starting in Nov 2022 I started getting a sporadic SERVICE TRAILER BRAKE SYSTEM warning light and chime. I have never towed a trailer using this trailer brake system on the vehicle, but the warnings come on sporadically. I have done some research and found this is not an isolated case as others have reported the same problem. Some owners have…
2018 GMC Sierra brakes problems
moderate 20 complaints filed with NHTSA · avg repair $450 · see brakes across all vehicles →
Failure mileage
Complaints
20
Recalls
0
Avg fix
$450
What stands out
No new NHTSA brakes complaint has been filed on this vehicle in over 3 years — the issue may be aging out of the active population.
The failure pattern owners describe
The most common complaint is a relentless "Service Trailer Brake System" warning and alarm that sounds repeatedly on the dash even when no trailer has ever been connected. Owners describe the alarm as so loud it makes the truck feel undriveable and cannot be dismissed by hitting buttons repeatedly. Dealers admit to owners that this is a known recurring issue affecting multiple trucks, with some owners replacing the defective switch or controller at out-of-pocket cost.
A second major issue is brake assist failure, where the brake pedal becomes hard to push and requires significant extra pressure to stop the vehicle. Some owners report needing to depress the pedal to the floor, with brake assist warnings lighting up on the dash. Dealers diagnosed vacuum pump failure as the root cause. Several owners found their vehicles matched existing recalls—like NHTSA 19V645000 or 20V603000—but their VINs were excluded from coverage despite identical symptoms.
Additional reports include ABS control module failure illuminating the ABS light, a brake line routed in a location vulnerable to road damage, and brake pedal responsiveness lag where the truck continues moving forward briefly after the driver shifts from gas to brake pedal, requiring hard braking to stop.
Same GMC Sierra brakes reports on nearby years: 2015 · 2017 · 2019 · 2020 · 2021
Failure modes owners describe
Faulty Trailer Brake System Warning
Persistent or recurring 'Service Trailer Brake System' warning light and audible alarm that sounds repeatedly on the dash even when no trailer is hooked up or has ever been connected to the vehicle. The alarm is loud, relentless, and causes driver distraction.
When: Starting several months after purchase or years into ownership; varies from occasional to constant within weeks
Symptoms owners cite: Service Trailer Brake System warning message on dash; Loud, persistent alarm that repeats continuously; Warning cannot be dismissed by repeated button presses; Extreme driver distraction due to noise and visual alert; No actual trailer connected or ever towed; Alert makes vehicle feel undriveable
Repairs/costs cited: Defective switch or dashboard controller replacement reported by owner at $127.14 (2022); some owners have replaced the controller at their own expense; pulling the trailer brake fuse temporarily stops the alarm
Recalls/TSBs owners mention: GM dealers acknowledge this is a known recurring issue across multiple owners; no formal recall noted in narratives for this specific failure
Brake Assist System Failure with Vacuum Pump Degradation
Brake pedal becomes hard to depress, requiring significantly more foot pressure to stop the vehicle. Brake assist warning light or message appears on the dash. Extended braking distance results. Root cause identified as brake vacuum pump failure or loss of brake pressure.
When: Between 37,000 and 135,000 miles; onset varies from a few months into ownership to later in vehicle life
Symptoms owners cite: Brake pedal requires excessive force to depress; Extended braking distance; Brake pedal feels soft or lacks pressure when depressed; Brake pedal vibrates or shakes during braking; Service Brake Assist warning light or message displayed; Difficulty stopping vehicle, especially at higher speeds or in emergency situations; Nearly resulted in rear-end collisions in some cases
Repairs/costs cited: Vacuum pump replacement needed; some vehicles were pending repair; one owner reported vacuum pump failure diagnosis at dealership but vehicle not repaired; brake pedal may vibrate with increased effort
Recalls/TSBs owners mention: Some owners aware of NHTSA recalls 19V645000 and 20V603000 for brake issues, but their VINs were not included despite identical symptoms; manufacturer directed one owner to NHTSA hotline; recall N202300860 exists but does not cover all affected vehicles with same symptoms
ABS Control Module Failure
ABS control module experiences internal failure, illuminating the ABS warning light on the instrument cluster. Vehicle owner initially unaware of the fault until light comes on while parked.
When: At approximately 112,000 miles
Symptoms owners cite: ABS warning light illuminated; No warning prior to light activation; Vehicle parked and undriven when failure detected
Repairs/costs cited: ABS control module replacement required; vehicle was not repaired at time of complaint
Recalls/TSBs owners mention: Owner researched NHTSA Campaign Number 00V055000 (Service Brakes, Hydraulic) but VIN was not included in recall coverage
Brake Line Routing Design Hazard
Left rear brake line is installed in a location where road hazards could strike and tear it away, creating risk of total brake failure. Owner reports observing same design flaw on multiple identical vehicles on dealer lot.
When: Present from manufacture
Symptoms owners cite: Brake line routed in vulnerable location; Susceptible to damage from road debris or hazards; Potential for complete loss of braking power if line ruptures
Brake Pedal Responsiveness Issue
When shifting from accelerator to brake pedal, the truck does not immediately respond to brake input. Engine surge or throttle lag persists briefly after foot leaves gas pedal, causing vehicle to continue moving forward momentarily despite brake application.
When: Intermittently during normal driving, especially in low-speed traffic situations
Symptoms owners cite: Vehicle continues moving forward after brake pedal depressed; Delay in brake response after accelerator release; Occurs in bumper-to-bumper traffic at slow speeds; Happens intermittently, duplicatable by owner; Requires hard pumping of brakes to stop vehicle
Synthesized from 20 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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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 brakes problem on the 2018 GMC Sierra?
It's a documented issue but not catastrophic. 20 complaints have been filed. Repairs average $450 and most owners catch it before it causes a breakdown.
At what mileage does the brakes typically fail?
Across the 8 complaints that reported odometer mileage, most brakes failures cluster between 20,305 and 112,000 miles, with the median around 37,000. A quarter of owners report trouble before 20,305; a quarter make it past 112,000. 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 $450 for brakes 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 brakes?
No active recalls currently cover brakes 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/2018/GMC/Sierra.
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.