Toyota Sienna loss of power problems

Filed Nov 6, 2026 · Transmission · AZ

Since 2018–2019, our 2018 Toyota Sienna has had recurring drivability and suspected transmission problems, including stalling, failure to engage or accelerate when the accelerator is pressed, rough idle, hesitation, and harsh shifting. We reported these concerns to Toyota and filed an the federal safety agency complaint during our first year of ownership. The problems have continued intermittently for years and now include transmission whining, slipping, delayed gear engagement, irregular shifting, and reduced power. Unexpected stalling or failure to accelerate creates a safety risk when entering traffic, crossing intersections, or avoiding hazards. On October 19, 2026, AAA inspected the vehicle following a four-wheel-drive malfunction warning. Its October 20 invoice documents UA80F eight-speed transmission-related fault codes P0740-7E, P2713-7F, and P2756-7F and notes possible sticking valve-body solenoids. Toyota's own Technical Service Bulletin T-SB-0160-18 (issued December 17, 2018; revised May 11, 2021), titled "Transaxle Whine Noise, Harsh Shift, MIL ON, or Reduced Power," applies to certain 2017–2018 Siennas and lists these exact three codes (formatted P07407E, P27137F, P27567F). Toyota's Customer Support Program ZJC, Policy Bulletin POL19-04 (2019), also acknowledges transmission whine, harsh shifting, reduced power, and warning lights in certain UA80-equipped vehicles and describes a possible assembly defect involving a washer tab and loosening internal nut. An authorized Toyota dealer evaluated the vehicle October 24–30, 2026, after receiving AAA's findings but reported it could not reproduce a warning light and that the VIN/transmission serial number were outside program limits. No transmission repair was performed. The vehicle remains unrepaired. Please investigate whether this longstanding safety-related failure affects vehicles beyond Toyota's stated production cutoff.

Filed Jul 17, 2026 · Engine · NJ

I am submitting this complaint to request that the federal safety agency document and evaluate what may be a broader defect affecting certain Toyota Sienna vehicles and determine whether it presents a potential safety-related defect trend. My 2015 Toyota Sienna was diagnosed by an authorized Toyota dealership with an external rear-bank head gasket leak. A head gasket is a critical engine component, and failure can result in coolant loss, engine overheating, reduced engine performance, stalling, or complete vehicle disablement. These conditions may create a safety risk, particularly if they occur while driving in traffic or at highway speeds. An authorized Toyota dealership confirmed the diagnosis and submitted a goodwill assistance request to Toyota. The dealership noted my history as a repeat Toyota customer and recommended that assistance be provided. Toyota denied the goodwill request based on the vehicle's age and mileage. I subsequently appealed through Toyota's customer relations process, and the denial was upheld. I understand that the federal safety agency does not resolve individual warranty or customer-assistance disputes. My purpose in submitting this complaint is to request that the federal safety agency determine whether similar reports exist involving premature head gasket failures in this model year or related vehicles and, if warranted, evaluate whether a broader defect trend exists that could present a safety concern. Potential safety consequences include engine overheating, loss of power, stalling, and unexpected vehicle disablement. The vehicle has been maintained in accordance with manufacturer recommendations and has not experienced any overheating event that would reasonably explain a premature head gasket failure. Thank you for your consideration and for documenting this complaint as part of the federal safety agency's review of potential vehicle safety issues. Respectfully, Vehicle Owner

Filed Jul 14, 2026 · Transmission · FL

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 diagnostic trouble codes match those described in Toyota TSB T-SB-0160-18 ("Transaxle Whine Noise, Harsh Shift, MIL ON, or Reduced Power") for the UA80 8-speed transmission. This is the same failure mode Toyota acknowledged in Customer Support Program ZJC, which attributes the defect to a washer/locking tab that was not sufficiently bent during assembly, allowing an internal nut to loosen and causing progressive internal damage. However, this vehicle's transaxle serial number falls outside the range covered by ZJC, so Toyota has not provided coverage despite the identical defect and symptoms. This represents a safety concern. Based on documented failures of this transmission across the UA80 platform, the condition can progress to loss of power, limp mode, or sudden loss of forward propulsion while driving — including at highway speed and without further warning — creating a risk of a crash or of being stranded in traffic. The vehicle has been maintained through authorized Toyota service. I am requesting that the federal safety agency investigate whether the UA80/UA80F transmission defect warrants a broader safety defect determination and recall, given the volume of similar complaints across affected model years INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

Filed Jul 11, 2026 · Transmission · CA

I, as well as other owners of 2017–2018 Toyota Highlanders and 2017–2018 Siennas are experiencing serious transmission issues—including high-pitched whining, erratic shifting, clunks, hesitation, and premature failure. My 2017 Toyota Sienna has the UA80 8-speed automatic transmission at issue and started whining upon acceleration in March/April 2026 timeframe. It has always had the clunking and hesitation problem. According to Gears Magazine, the issue stems from a flawed assembly process involving the counter drive gear support. A locking tab meant to secure a vital retaining nut was not bent properly during factory assembly. This leads to gear movement, internal wear, whining, and eventually failure. Unknown to me, in 2019, Toyota had acknowledged the problem in Technical Service Bulletins T-SB-0160-18, T-SB-0008-21, which only go to dealers, and implemented a limited Customer Support Program (CSP ZJC)—but only offered coverage to a narrow group of VINs, not to all VINs for model years that have these transmissions. My car is experiencing these same symptoms. My Toyota Dealer confirmed this problem and recommended a transmission replacement for $11,000 including labor. They said my VIN was not included in the Customer Support Program. Driving with a failing transmission is highly dangerous. A bad transmission can cause sudden power loss causing the car to halt to a sudden stop, unintended acceleration, or my car might get stuck in neutral while driving. I could lose control or be unable to get to the shoulder on the highway, cause a rear-end collision, or get stuck in busy traffic. DESIRED OUTCOME REQUEST: My VIN should be covered under the Customer Support Program in the category of cars that are “less than 10 years old regardless of mileage” or a full recall of all VINs of these model years with these transmissions should be executed. Thank you.

Filed Jun 22, 2026 · Fuel system · FL

While driving at speed, the vehicle suffered a sudden and complete loss of engine power and stalled in traffic. The vehicle was diagnosed by an independent mechanic who found a failed factory-installed Denso fuel pump module. This failure mirrors Toyota Safety Recall 20TA02 (the federal safety agency Campaign 20V012) for the exact same model year 2017 Toyota Sienna, but my specific VIN is currently excluded from the recall list. The un-recalled defective component created an immediate highway safety hazard as me and my family were left stranded in the middle of the road. We waited for hours at the risk of oncoming traffic until we were able to have a tow truck lift the van and take to the nearest repair facility (an independent service center - Goodyear Auto Service). The repair facility diagnosed the problem and confirmed that the fuel pump failed to generate enough pressure causing the vehicle to stall and not start again. To correct the problem, the fuel pump was replaced with an OEM toyota fuel pump module assembly.

Filed Apr 26, 2026 · Engine, Fuel system · FL

The vehicle is a 2020 Toyota Sienna. While driving, the engine suddenly shut off without warning, creating a dangerous situation and loss of power. This occurred while transporting children, increasing the safety risk. A mechanic inspected the vehicle and diagnosed a failure of the low-pressure fuel pump. The problem appears intermittently — sometimes the vehicle runs normally, and other times it stalls or loses power. The check engine light has turned on and off. This issue matches the known defect related to the Denso fuel pump recall affecting many Toyota vehicles from similar model years. However, my VIN is not included in the recall. This is a serious safety concern because the engine can shut off unexpectedly while driving, which could lead to an accident. I believe this vehicle may have the same defective component as those included in the recall, even though it is not currently listed. The issue has been confirmed by an independent mechanic and the vehicle is available for inspection if needed.

Filed Apr 17, 2026 · Transmission · TX

Loss of power highway speeds, jerky shifting, “sealed” transmission leaking fluid. Check engine light and service required light. I have noticed poor performance with this vehicle before and reported it to the dealer to no avail. Toyota has enacted “customer support program ZJC” but the dealership will not honor.

Filed Jan 20, 2026 · Transmission · 120,000 miles · CO

The contact owns a 2017 Toyota Sienna. The contact stated that while starting the vehicle, reversing, and then while driving 20 MPH, there was an abnormal whining sound coming from the front of the vehicle. A dealer was contacted. The vehicle was taken to the dealer and was currently being diagnosed. The vehicle was not repaired. The contact related the failure to Technical Service Bulletin: TSB-0160-18 (Transaxle Whine Noise, Harsh Shift, MIL ON, or Reduced Power); however, the VIN was not included in the bulletin. The manufacturer was notified of the failure and referred the contact to the federal safety agency Hotline to report the failure. The failure mileage was 120,000.

Filed Nov 17, 2025 · Brakes, Electrical · MD

Vehicle: 2011 Toyota Sienna XLE VIN: [XXX] Mileage: ~204,800 Incident Date: [XXX] Recent Service: Oil change, tire rotation, brake inspection, and multipoint inspection performed on November 10, 2025 at Fitzgerald Toyota Gaithersburg (Maryland). Description of the Defect: On [XXX] while driving with my child in the vehicle, my 2011 Toyota Sienna experienced a sudden and dangerous failure. A strong burning smell entered the cabin, the ABS warning light illuminated, and then wheels locked up while the vehicle was in motion. At the same time, the steering wheel locked, making the vehicle impossible to steer. The engine immediately lost power and shut down in the middle of the roadway. The vehicle would not restart and had to be towed. This failure occurred four days after dealership service at Fitzgerald Toyota Gaithersburg, which included an oil change, tire rotation, and brake inspection. The dealership initially claimed the failure was due to a “dead battery,” and the following day changed the explanation to a “shorted alternator.” A weak battery or alternator failure does not explain a mechanical wheel lock or steering wheel lock while driving. The dealership has refused to provide diagnostic documentation or photographs of the components involved. This incident presents a significant safety hazard, and if it had occurred at highway speeds, it could have resulted in a severe crash. I am reporting this to request investigation into a potential safety defect involving the steering system, braking/ABS system, electrical system, or related components. Safety Risk: High. Loss of steering control + wheel lock + engine shutdown presents an immediate crash hazard. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)

Filed May 9, 2025 · Brakes, Driver assistance · OH

The Traction Control System commonly malfunctions while making turns on curving road sections. I will lose power through turns as the TCS light blinks on my dashboard and makes a beeping sound. On some occasions the brakes will automatically engage in the tire that the car perceives as experiencing slippage. This problem is continuously worsening and commonly endangers me and my passengers, as the car engages brakes or cuts power to the engine at unexpected and in opportune times.