2021 Toyota Prius Problems: 2 Issues Every Owner Should Know

2021 model year · NHTSA recalls, manufacturer TSBs, and owner forum reports · Updated May 2026

According to Au7o's research across NHTSA recalls, manufacturer TSBs, and owner forum reports, the 2021 Toyota Prius has 2 documented known issues, with 1 rated critical. The most serious is Catalytic Converter Theft Vulnerability ($150-$3,000 repair). Across all issues, repair costs range from $150 to $3,000. DIY maintenance guides at au7o.io.

All 2 Known Issues

On the 2004-2025 Toyota Prius, the Toyota Prius is the single most targeted vehicle for catalytic converter theft in the United States. The Prius catalytic converter contains higher concentrations of precious metals (palladium, rhodium, platinum) than most vehicles because the hybrid system results in a cleaner-running engine that preserves the catalyst metals. The converter is also easily accessible under the vehicle and can be cut out with a battery-powered reciprocating saw in under 60 seconds. Thieves sell stolen converters for $100-$300 to recyclers who extract metals worth $500+. Gen 2 (2004-2009) and Gen 3 (2010-2015) Prius are the most targeted.

This issue also affects: BMW X6, Chevrolet Equinox, Chrysler 200

Common Symptoms

Extremely loud exhaust noise when starting the vehicle
Vehicle sounds like a race car or has no muffler
Check engine light for catalyst efficiency codes
Visible saw cuts on exhaust pipe under vehicle
Reduced engine performance and rough running

How to Fix

Install a catalytic converter anti-theft shield or cage ($150-$400 installed). Popular options include CatClamp, MillerCAT, and CatShield. These devices make the converter much harder and more time-consuming to steal. Park in well-lit areas and garages when possible. Engrave your VIN on the converter ($30-$50 at a muffler shop) to aid in recovery. Some owners install motion-activated alarms or cameras. If your converter is stolen, replacement costs $1,500-$3,000 for an OEM converter, or $500-$1,000 for an aftermarket CARB-compliant unit (required in California).

What Owners Are Using

Parts and tips from 0+ owners who fixed this issue

TipInstall a CatShield or MillerCAT guard immediately. It costs $200-$400 and takes 30-60 minutes to install. This is non-optional for Prius owners — catalytic converter theft is a matter of when, not if.
TipCheck if your insurance covers catalytic converter theft under comprehensive coverage. Many policies cover it with just the deductible. File a police report immediately if stolen.
UpgradeWalker catalytic converter — EPA-compliant direct fit (Walker Catalytic Converter)
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UpgradeMagnaFlow catalytic converter — high-flow performance option (MagnaFlow Catalytic Converter)
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Typical repair cost:$150 - $3,000

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Community Reported

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On the 2004-2025 Toyota Prius, the 12V auxiliary battery in the Prius is critical for powering the vehicle computer systems that must boot up before the hybrid system can start. Unlike conventional cars where a weak battery can still crank the engine, a dead 12V battery in the Prius means the vehicle will not start at all — no dashboard lights, no READY mode, nothing. The small 12V battery (typically a Group S46B24R) drains faster than in conventional vehicles because it powers always-on systems like the smart key receiver, security system, and clock. The battery typically lasts only 3-5 years, shorter than in conventional vehicles.

This issue also affects: Fiat 500e, Kia Niro, Toyota Prius V

Common Symptoms

Vehicle will not enter READY mode
No dashboard lights or display when pressing start button
Smart key system not detecting key fob
Clock resetting or losing time
Intermittent electrical glitches before total failure
Vehicle will not start after sitting for several days

How to Fix

Replace the 12V auxiliary battery every 4-5 years as preventive maintenance. The battery is located in the right rear of the cargo area (not under the hood). OEM Toyota replacement costs $200-$300 installed at the dealer. Aftermarket AGM batteries (Optima Yellow Top, Odyssey) run $150-$250 and can be installed DIY in 15 minutes. If the battery dies, a jump start to the 12V terminal under the hood (or in the fuse box on Gen 4) will get the car started. Consider a battery tender/maintainer if the car sits for more than a week at a time.

What Owners Are Using

Parts and tips from 0+ owners who fixed this issue

TipMark your calendar to replace the 12V battery every 4 years proactively. A dead 12V battery at the worst possible time is the most common Prius "breakdown" and it is 100% preventable. The battery is in the rear cargo area, not under the hood.
TipIf your Prius sits for more than a week, connect a battery tender to the 12V battery. A CTEK or Battery Tender Junior ($30-$50) will keep it charged and extend battery life significantly.
UpgradeHigh-performance AGM battery with excellent cold cranking amps and deep cycle capability (Optima RedTop AGM Battery)
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UpgradeOEM-quality replacement battery with reliable performance (ACDelco Professional AGM Battery)
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UpgradeAutomatic battery maintainer to prevent parasitic drain issues during storage (Battery Tender Junior 12V Battery Charger Maintainer)
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UpgradeAutomotive relay replacement set for common relay failures (Bosch Automotive Relay 5-Pin 12V)
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UpgradeDigital multimeter for diagnosing fuse, relay, and module electrical faults (Innova Digital Multimeter)
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Typical repair cost:$150 - $300

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Community Reported

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Frequently Asked Questions

What are the most common Toyota Prius problems?

According to Au7o's research across NHTSA recalls, manufacturer TSBs, and owner forum reports, the 2021-2021 Toyota Prius has 2 documented issues. The most frequently reported are: Catalytic Converter Theft Vulnerability, 12V Auxiliary Battery Drain and Failure. Of these, 1 is rated critical and should be addressed promptly.

Is the Toyota Prius reliable?

The 2021-2021 Toyota Prius has 2 known issues compiled from NHTSA recalls, manufacturer TSBs, and owner forum reports. 1 issue is rated critical: Catalytic Converter Theft Vulnerability. Prospective buyers should inspect for these issues and factor potential repair costs into their purchase decision. Regular maintenance following the manufacturer's schedule helps prevent many common problems.

How much does it cost to fix common Toyota Prius problems?

Repair costs for known Toyota Prius issues range from $150 to $3,000, depending on the specific problem and whether you choose DIY or professional repair. The most critical issue, Catalytic Converter Theft Vulnerability, typically costs $150-$3,000 to repair. Au7o provides step-by-step DIY maintenance guides that can help reduce repair costs.

What is the 2004-2025 Toyota Prius Catalytic Converter Theft Vulnerability?

The Toyota Prius is the single most targeted vehicle for catalytic converter theft in the United States. The Prius catalytic converter contains higher concentrations of precious metals (palladium, rhodium, platinum) than most vehicles because the hybrid system results in a cleane… Repairs typically run $150-$3,000. Severity: high.

What is the 2004-2025 Toyota Prius 12V Auxiliary Battery Drain and Failure?

The 12V auxiliary battery in the Prius is critical for powering the vehicle computer systems that must boot up before the hybrid system can start. Unlike conventional cars where a weak battery can still crank the engine, a dead 12V battery in the Prius means the vehicle will not… Repairs typically run $150-$300. Severity: medium.

2021 Toyota Prius Problems: 2 Issues Every Owner Should Know

All 2 Known Issues

2004-2025 Toyota Prius: Catalytic Converter Theft Vulnerability#

Common Symptoms

How to Fix

What Owners Are Using

Research This Issue

2004-2025 Toyota Prius: 12V Auxiliary Battery Drain and Failure#

Common Symptoms

How to Fix

What Owners Are Using

Research This Issue

Other Toyota Models

Frequently Asked Questions

What are the most common Toyota Prius problems?

Is the Toyota Prius reliable?

How much does it cost to fix common Toyota Prius problems?

What is the 2004-2025 Toyota Prius Catalytic Converter Theft Vulnerability?

What is the 2004-2025 Toyota Prius 12V Auxiliary Battery Drain and Failure?