2021 Subaru Forester: start-stop system problems

Filed Nov 1, 2026 · Electrical, Engine · TX

When coming to a stop, the auto start/stop system shuts the engine off and it fails to restart. All dashboard warning lights illuminate. The vehicle must be shifted to Park and restarted manually with the start button. The component that failed is the auto start/stop system; the exact cause is UNKNOWN. The vehicle is available for inspection upon request. This put safety at risk because the vehicle was left immobile in live traffic at stops until it could be restarted. There were no warning lamps or symptoms before the failure; the warning lights come on when the failure occurs. The vehicle was inspected by Gillman Subaru Southwest on October 229, 2026, and the dealer stated the battery performance was bad and in critical condition.

Filed Oct 3, 2026 · Engine, Fuel system · CA

On two separate occasions, less than one year apart after Subaru Service replaced my battery with a “larger” battery without my knowledge my vehicle suffered sudden, catastrophic electrical failure while moving in active highway traffic, causing an immediate loss of propulsion and creating a life-threatening safety hazard. This has happened two times the second time less than a year after the “larger” battery replacement. This car has less than 50,000 miles on it and has a perfect service record all done at AutoNation Subaru Carlsbad. We refuse to drive this car, even though it has been serviced and a new battery has, yet again, been installed. We have no faith in this car and are not willing to put ourselves in a life-threatening situation again. We also do not feel comfortable selling this car, even though we have received many above market offers. We do not feel that we can sell this car in good conscience to an unknowing next victim. It is unsafe to drive and can lose power at any moment while driving without any explanation given from Subaru. The first battery failure occurred prematurely in August 2025. Asked repeatedly why a car battery would fail while driving? Could not get a straight answer except that someone finally said it could possibly be from the auto stop start system The new larger battery failed less than one year later in August 2026, so it didn’t even last a year and it was larger. The service department at AutoNation Carlsbad told me my car passed all the test and I have nothing to worry about. This goes against any common sense. How could this happen 2 times where no issue has been disclosed. Both situations were extremely traumatic and dangerous and I feel lucky that I was able to come out of it. I’m not sure the next time would be the same. We are not able to drive this car because common sense tells us there is a bigger issue going on. So far we’ve communicated with Subaru of America and were denied California Lemon law without reason.

Filed Jul 2, 2026 · Electrical, Engine · WI

My 2021 Subaru Forester has a recurring, worsening defect in the Idle Stop/Start (ISS) system that creates a stalling hazard. When ISS shuts the engine off at a stop, the engine intermittently fails to restart when I try to move again. It cranks progressively slower, warning lights illuminate, a continuous alert sounds, and the vehicle cannot proceed until I shift to Park and restart manually. This has left me immobile in live traffic at lights, stop signs, and mid-turn. The system also attempts to shut down in unfavorable moments, such as mid-turn, or as I am already releasing the brake (meaning it was depressed only lightly or briefly); it then tries to restart while still mid-shutdown, producing a pronounced shake. This is not a battery-charge problem. It has occurred even when the battery tested above its rated cold-cranking amps, and after each failure the engine restarts smoothly by manual start, indicating the starter, engine, and fuel systems function normally. I raised this before 2024, but it was not recorded until May 2024. At that visit the dealer performed the TCM reprogramming in Service Bulletin 16-147-24 (Forester, auto start/stop engine speed drop on restart) plus an ECM update. A later visit added another ECM update. A dealer has now identified yet another TCM reprogramming, quoted for a fee. The failure has persisted across all of these updates. Dealer staff acknowledge repeated customer complaints with these exact symptoms and say there is no known effective fix. Because ISS cannot be permanently disabled through any factory control, I must remember to disable it manually every drive to avoid a restart failure in traffic. The vehicle is available for inspection. This is an ongoing, unresolved safety defect that repeated manufacturer software remedies have failed to correct, and it can leave the vehicle disabled in live traffic.

Filed Jun 3, 2026 · Electrical · FL

2021 Subaru Forester The vehicle has experienced recurring electrical and battery-related issues for several years. The original battery was replaced by the Subaru dealer with a larger-capacity battery because of repeated starting concerns. The replacement provided only temporary improvement. The vehicle continues to experience rough starting on a regular basis, even after installation of a newer aftermarket battery with a higher cold-cranking-amp rating. The current battery is approximately five months old. The most significant safety concern occurs during Auto Start-Stop operation. On multiple occasions, the engine has shut off at a stop as intended, but then failed to restart when attempting to move again. When this occurs, multiple warning lights illuminate on the dashboard and the vehicle is unable to proceed until it is shifted into Park and restarted manually. Because of this issue, I now disable the Auto Start-Stop feature on every drive to avoid a potential failure to restart while in traffic. The issue has been ongoing for years and has occurred with multiple batteries, including the dealer-installed replacement battery and a newer aftermarket battery. The dealer suggested that an aftermarket dash camera could be contributing to battery drain. The dash camera was disconnected, but the problem continued. I am concerned that failure of the vehicle to restart after Auto Start-Stop operation could leave the vehicle disabled in traffic and create a safety hazard. The condition appears to involve the vehicle’s electrical system, battery management system, charging system, Auto Start-Stop system, or a combination of those components. The vehicle is available for inspection upon request.

Filed May 3, 2026 · WA

I am filing this complaint regarding a recurring and dangerous safety issue with my 2021 Subaru Forester. The auto stop/start feature intermittently fails to restart the engine after it shuts off when stopped. When this occurs, multiple dashboard warning lights come on, an alarm sounds, and the vehicle requires putting the transmission into "Park" and shutting it down completely before it will start again. This has happened multiple times at intersections, traffic lights, and freeways during rush hour (stopping and starting frequently), leaving me temporarily stranded in live traffic. The local Subaru dealership service department was unable to replicate the issue, however upon inspecting the vehicle's charging system, the battery was found unable to hold charge from the alternator and was replaced on June 9th, 2025. Now after less than 1 year of replacing the battery, the problem persists. I have been made aware of TSB 16-118-24R (TCM reprogramming for auto start/stop restart failure) and TSB 09-80-21 (Thermostatic Control Valve failure) which appear directly related to this issue. This is a serious safety hazard. A vehicle that cannot restart in live traffic puts the driver and other motorists at significant risk of a crash. I am requesting that the federal safety agency investigate this issue and consider a formal recall.

Filed Apr 1, 2026 · Electrical, Engine · TN

Automatic start/stop fails to turn car on - intermittent. Taken it to Subaru detailer miltiple times and paid for services to correct the issue, but the issue persists. Fist time - replaced the battery in July 2025. 2nd time, went on a ride along for 1 hour, issue did not happen, replaced spark plugs, issue persists. 3rd time, updated TCM software, issue still persists. Subaru of America is aware of the issue and have not gotten a resolution either.

Filed Dec 4, 2025 · Driver assistance · FL

I am writing to file a formal complaint regarding repeated, severe, and dangerous malfunctions of the vehicle's engine Start/Stop (Idle Stop) feature. The system is failing to operate as intended, resulting in the engine stalling while the vehicle is in motion or under crucial driving circumstances, creating significant safety hazards. History of Incidents I have experienced four separate incidents where the engine unexpectedly stalled or shut down, creating extreme risk: Incident 1 (Railroad Tracks): The engine stopped while I was actively driving over railroad tracks. The car stalled on the tracks, and within seconds of the engine restarting, the crossing gates came down and a train passed. I narrowly avoided being hit by the train, missing the impact by approximately ten seconds. Incident 2 (Heavy Traffic/Bridge): During heavy, back-to-back traffic as a bridge (PGA bridge) was opening, the car momentarily stopped and then resumed movement. The unpredictable stopping motion created a severe risk of being rear-ended, as the following vehicle would have had difficulty anticipating the sudden, unintended stop. Incident 3 (December 2025): While taking a right turn, the engine stopped suddenly, with dash lights blinking, during only a slight pause in vehicle movement. This occurred while the vehicle was still maneuvering. Incident 4 (The following day): The engine stopping malfunction described in Incident 3 occurred again the next day. Attempted Repair and Ongoing Concern Two years ago, the dealership installed a new battery following the first two incidents. However, the problem has now recurred this week (December 2025). The dealership has informed me that using a third-party device to permanently disable the Start/Stop function would void the powertrain warranty. Causing Mechanical Stress: I believe the continuous, potentially faulty activation is putting unnecessary stress on the battery, electrical system, and engine components, which may ultimately shor

Filed Nov 10, 2025 · Acceleration, Electrical · MD

My Subaru has an auto start/stop. I was at a complete stop, making a left-hand turn, and my car completely shuts off with the following message: For safety, auto restart disabled; eyesight with a \ through the words, put car in park and restart vehicle. In the time it took me to put the car in park and restart, I was almost T-bone. This was terrifying. This had happened on previous occasion in stop and go traffic which is dangerous because my car has come to a complete stop without any warning to me where the driver behind me There are no warning symbols, warning lights, or any type of signal or symptoms to notify me that my car was going to stop completely.. Typically I remove my foot from the break, the car starts and then I put my foot on the gas pedal and the car moves forward. In the situations described above the car just stopped.It just flat out stopped. There’s never been any indication or signal to indicate the car is not going to restart The retailer replaced my battery and said it should help. I called the Subaru factory rep who was of no help. She said she is not a trained technician and all that she could offer to do was to contact the retailer. The dealer was not able to reproduce the problem. The retailer replaced the battery without any response about the safety issue. I asked if Subaru had a safety board I could report this too and the factory rep said no, but she will document it and they’ll do an internal review to see if we have any other similar issues reported, however, they will not contact me because they don’t talk to the public about these issues. I told her there are hundreds of these if not, thousands concerns online stating the same issue. The rep said she would document my concern. Documentation is good if there’s a fix but I’m concerned about the unnecessary death of a driver.The retailer also advised I could do the auto start override, I’m trying to make a point of how serious of a safety issue this problem can be. Thank you!

Filed Oct 31, 2025 · Electrical, Engine · GA

The vehicle has experienced four separate engine shutdowns while stopped in traffic. Each time, the engine turned off unexpectedly, requiring a manual restart. One incident occurred near a railroad crossing with my child in the car. The vehicle also lurches forward at low speeds and hesitates when accelerating after being stopped. These issues persist despite service visits. I believe they may relate to Technical Service Bulletins regarding the Auto Start/Stop and battery systems (TSBs #16-147-24, #10232217, #07-218-23R, #10251098). Subaru service staff have acknowledged awareness of these problems. I’m submitting this complaint to ensure the safety risk is documented and investigated.

Filed Jun 27, 2025 · Electrical, Engine · CA

The Auto-Stop/Start feature frequently fails to properly restart the car, often causing the car to stall during the restarting process, leaving me effectively disabled on a busy road. The battery has already been replaced once.

Filed Jun 12, 2025 · Electrical · IA

My vehicle is equipped with automatic start/stop system. In early 2024, I began having issues with sluggish restart during the start/stop cycle. I took it into the dealer at that time, who stated it required a software update and charged the battery. The issue persisted. It was more serious, as it was not just sluggish on the restart, but the restart would fail and stall the car. This happened in heavy traffic, which was very scary and unsafe. I took the vehicle back into the dealer in late 2024 for the same issue. They did another software update and charged the battery again. They recommended that we purchase a new battery. One month later, we purchased an upgraded AGM battery, as it was recommended for auto start/stop systems. The issue continued to persist. First, with sluggish restart. Later, the auto start/stop system failed again in heavy traffic. We took the vehicle in again, and again the dealer stated it was the battery. They recommended we purchase a new battery. It was explained the battery was 6 months old, and the issue has never been fixed. Further, it was pointed out that the car could be restarted manually with the push button ignition, after a start/stop system failure. That led us to believe it was not a battery failure, but a deeper system failure. The dealer continues to assert it is the battery, even though it happened with a factory battery and a new, upgraded, battery. Neither of the batteries have failed testing, and report as "good" on the diagnosis forms. We believe there is a system issue, that is causing issues with the auto start/stop system, and is not being identified by the dealer. It is a safety issue, as it has happened in heavy traffic several times. We have attached diagnostic reports from March 2024 and June 2025, but cannot find the October 2024 diagnostic report.

Filed May 9, 2025 · FL

Automatic stop activated at traffic light. When the brake was disengaged, the star would not start. The occupant was stalled at the traffic light during rush hour in a thunderstorm with limited visibility for approximately 15 minutes. Winter Haven Police Department was dispatched but did not arrive probably due to other weather-related traffic situations. After that time, the engine did start and was moved into a lot without incident. The good Samaritan that assisted stated he had just stopped down the street on another disabled vehicle in traffic due to malfunctioning auto stop/start. Here is the issue. The alternator and battery have both been checked twice and were in proper order. The OE battery was in use. There was no warning to indicate any issue with the batter. In fact, the Subaru app was reporting the vehicle was operating normally while the vehicle was dead in the road. I work with a local law enforcement agency and have worked fatal crashes on that road. It is unacceptable for the vehicle to not have some type of redundant system to warn owners that the vehicle battery is failing before they are thrust into a possible deadly roadway breakdown.