TT: Some 2014-2021 model year vehicles equipped with Dynamic Torque Control AWD system may experience a ?Noise? or ?Abnormal Operation? condition from the rear differential front coupling. In some cases, even an ?AWD System Message? with or without a DTC may be present with or without other conditions present.
full bulletin at NHTSA ↗2018 Toyota Sienna powertrain problems
moderate Owners of the 2018 Toyota Sienna have filed 18 NHTSA complaints about the powertrain at roughly $2,500 to repair (U.S. federal records, as of August 2026). Source: NHTSA Office of Defects Investigation. See powertrain across all vehicles →
Complaints
18
Recalls
0
Avg fix
$2,500
| Model year | powertrain complaints |
|---|---|
| 2014 Sienna | 6 |
| 2015 Sienna | 10 |
| 2016 Sienna | 3 |
| 2017 Sienna | 34 |
| 2018 Sienna (this page) | 18 |
| 2019 Sienna | 7 |
| 2020 Sienna | 8 |
When does it fail?
Of the 18 powertrain complaints filed for the 2018 Toyota Sienna, here's the actual mileage breakdown — failures cluster heaviest at 25,000-50,000 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
Powertrain accounts for 26% of all owner complaints filed against this vehicle, across 5 categories tracked.
No new NHTSA powertrain complaint has been filed on this vehicle in over 7 years — the issue may be aging out of the active population.
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.
TT: Currently under investigation. Please contact TAS if you have a vehicle that exhibits a leak from the Transmission Side Cover with no signs of damage or other conditions unrelated to regardless of miles or months in service. If it?s a Sunday or holiday continue with diagnosis and repair, save all parts and details, contact TAS on the next available work day and review details with TAS engineer.
full bulletin at NHTSA ↗TT: Some 2018-2020 model year UA80/UB80 transmission equipped models may experience a leak from the Transmission Side Cover. This issue is currently under investigation. Vehicles are being sought regardless of months in service or mileage. Only seeking vehicles with leaking transmissions with no other signs of damage to the side cover.
full bulletin at NHTSA ↗Customer Support Program Bulletin: Toyota has received reports indicating potential symptoms, such as a whine noise from the transmission while driving, harsh shifting, reduced power, and master warning light/check engine light illumination, in the subject vehicles that are equipped with a model UA80 transmission. There is a possibility that a washer tab, designed to prevent the loosening of a nut inside the affected transmissions, was not sufficiently bent during assembly. This could lead to the nut loosening and, over time, lead to the symptoms described above.
full bulletin at NHTSA ↗TSB: REVISION NOTICE July 01, 2019 Rev2: ? Applicability has been updated to 2019 ? 2020 model year Toyota vehicles. ? The Techstream Preparation and Process Overview sections have been updated. October 30, 2017 Rev1: ? Applicability has been updated to include 2018 model year vehicles. Any previous printed versions of this bulletin should be discarded. SUPERSESSION NOTICE The information contained in this bulletin supersedes SB No. T-SB-0012-13. Service Bulletin No. T-SB-0012-13 is obsolete and any printed versions should be discarded. Be sure to review the entire content of this bulletin before proceeding. Flash reprogramming allows the Electronic Control Unit (ECU) software to be updated
full bulletin at NHTSA ↗Source: NHTSA manufacturer communications. Bring the bulletin number to your dealer or shop.
The failure pattern owners describe
The 2018 Sienna's powertrain generates a consistent pattern of failures across these narratives. Transmission hesitation and delayed acceleration appear in nearly every complaint—owners describe 1–2 second delays before downshift, sluggish takeoffs on hills and at intersections, and dangerous merging behavior. Several owners pinpoint eco mode as the culprit, noting the transmission defaults to 3rd or 4th gear instead of 1st on startup, and no button fully disables it despite a visual "eco light" option. A whining noise from the transmission accompanies many of these complaints and worsens over time.
Transmission failure requiring complete replacement is documented at 89,000 miles (solenoid failure), 126,000 miles, 132,000 miles, and under 140,000 miles—well short of Toyota's traditional longevity reputation. One owner was denied coverage under Customer Support Program ZJC despite 83,700 Siennas listed as affected. Software updates have been issued, but owners report the problem returns within 1,000 miles.
Unrelated but notable: one owner reported the AC drain hose clogging at 3 years old, causing mold growth inside the vehicle with no warning indicator. Another noted unintended deceleration and loss of throttle response at 10,000 miles, along with winter braking shudder.
Same Toyota Sienna powertrain reports on nearby years: 2015 · 2017
Failure modes owners describe
Transmission Hesitation and Delayed Acceleration
The transmission fails to respond promptly to throttle input, causing delayed acceleration from stops or during passing maneuvers. Owners report 1-2 second delays before downshifting, and sluggish takeoff when the vehicle is in eco mode (default). This creates hazardous situations, especially on hills and highway merges.
When: Varies; documented from 10,000 miles through 140,000+ miles
Symptoms owners cite: Delayed response when pressing accelerator; Vehicle lugging in higher gears at low speeds; Failure to downshift when throttle is pressed; Slow takeoff at stops and intersections; Abrupt downshift followed by loud engine rev
Codes mentioned: P27137F
Repairs/costs cited: Transmission replacement; repair estimates $6,500–$7,000 cited by one owner
Recalls/TSBs owners mention: Customer Support Program ZJC exists for UA80 Transmission but many affected vehicles (including narrative #1 and #6) confirmed as not covered under the program despite 83,700 Siennas and 66,500 Highlanders listed as potentially affected
Transmission Whining Noise
A whining or humming sound emanates from the transmission, especially during acceleration. Owners report the noise worsens over time. Dealership diagnosis has confirmed transmission failure in multiple cases.
When: Several months to a year or longer; documented through 140,000+ miles
Symptoms owners cite: High-pitched whining or humming sound upon acceleration; Noise becomes progressively louder over months
Repairs/costs cited: Transmission replacement required in multiple cases
Recalls/TSBs owners mention: Referred to Customer Support Program ZJC coverage, which does not cover all affected vehicles
Eco Mode Transmission Logic Fault
The transmission defaults to eco mode on startup and exhibits aggressive hunting between gears and reluctance to downshift, making normal driving (especially hills and merging) feel underpowered. The eco mode light can be turned off visually but the underlying transmission programming persists. No button exists to fully disable eco mode.
When: Recurring during normal driving, particularly at startup
Symptoms owners cite: Transmission starts in 3rd or 4th gear instead of 1st; Reduced throttle input from a stop; Constant gear hunting; Struggles to accelerate up hills; Struggles to accelerate through intersections; Eco light can be hidden but problem persists
Repairs/costs cited: Software update available; one owner reports problem returned after approximately 1,000 miles post-update
Recalls/TSBs owners mention: Software updates offered but not permanently resolving the issue
Transmission Solenoid Failure
The transmission solenoid fails, triggering a warning light about electronic control malfunction. One owner reported complete transmission failure requiring full replacement.
When: At 89,388 miles
Symptoms owners cite: Slip during acceleration; Warning light: 'A malfunction in the electronic control of the engine, throttle, or automatic transmission has been detected'
Repairs/costs cited: Solenoid and entire transmission replacement required
Unintended Deceleration and Loss of Throttle Response
The vehicle decelerates on its own without driver input, and accelerator pedal input occasionally fails to produce engine response. One owner reported the vehicle suddenly stopping while reversing, with the engine revving as if the pedal were pressed.
When: At approximately 10,000 miles
Symptoms owners cite: Vehicle decelerates independently while driving 45–50 mph; Accelerator pedal does not respond when depressed; Vehicle suddenly stops reversing; engine revs unexpectedly; Failure recurs on several occasions
Repairs/costs cited: Vehicle not diagnosed or repaired
Stability Control and Braking Issues in Winter
The braking system shudders and the vehicle loses traction when driving in snow or ice, causing violent vibration. This may indicate transmission or stability control interaction.
When: At approximately 10,000 miles
Symptoms owners cite: Braking system shudders in snow or ice; Violent vibration and loss of traction
AC Condensate Drainage Failure Leading to Interior Mold
The AC condenser drain hose becomes clogged, allowing condensate to accumulate and leak onto interior upholstery. Mold develops inside the vehicle, creating a health hazard. The vehicle lacks a warning light or sensor to alert owners to this failure.
When: At 3 years old (approximately 2021)
Symptoms owners cite: Sound like water running inside the vehicle; Leak on driver and passenger seats; Mold growth on upholstery; No warning light or indicator prior to failure
Repairs/costs cited: Dealership performed expensive special mold remediation and interior disassembly; vehicle remained unassembled at dealership for 3+ months
Synthesized from 18 NHTSA owner complaints — unverified consumer allegations, summarized for patterns. The verbatim filings appear below.
What owners are reporting 5 most recent
My 2018 sienna le is experiencing acceleration problems. I had the software up dated but after approximately 1,000 miles the problem is returning. This problem is especially unsafe when merging onto the highway.
Delay in downshifting when throttle is pressed. A delay of 1 to 2 seconds occurs then abruptly downshifts and the engines revs loudly.
Transmission Whine and Hesitation. Low gear it will hesitate from stop. Know issue with this transmission. There should be a recall on all ua80 transmissions.
This is a reoccurring issue on numerous occasions but the transmission programming is a danger to drivers when it is in economy mode (the default setting when car starts up). The transmission constantly starts at a higher gear (3rd or 4th) and reduces throttle input from a stop. It makes for a slower takeoff when making a right turn on the stop sign because the engine would be lugging. Similarly…
Vehicle: 2018 Toyota Sienna XLE AWD, VIN [XXX], approximately 112,000 miles. Component: Power Train / Automatic Transmission (UA80F 8-speed). The vehicle has developed a pronounced whining noise from the transmission that rises with road speed, accompanied by harsh/rough shifting. A Toyota dealer inspected the vehicle and diagnosed a failing transmission requiring replacement. The symptoms and…
Had powertrain trouble with your 2018 Toyota Sienna?
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 2018 Toyota Sienna?
It's a documented issue but not catastrophic. 18 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?
Based on the 18 complaints filed, powertrain issues most often appear around 61,500 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 $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/2018/Toyota/Sienna.
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.