Why does my Toyota Sienna say 'Check hybrid system' or die overnight?

Short answer: Owners trace dead Siennas to a weak original 12V battery and faulty kick sensors draining it, and 'Check hybrid system' warnings to problems like corroded rear AWD wiring or a high-voltage fault. Have the 12V load-tested, ask about kick sensors, and if a hybrid warning comes with code P0AA6, the dealer needs to trace the high-voltage fault.

Symptom: A 'Check hybrid system' warning appears, the van won't go into Ready, or it's dead after sitting overnight.

What to check first

1. Have the 12V battery load-tested. A load test puts a real demand on the battery. A plain voltmeter reading can look fine on a battery that can't deliver power.
2. Ask the dealer about kick sensor drains if it dies overnight.
3. Ask for the exact codes, such as P0AA6.
4. If you have AWD, ask them to inspect the rear motor wiring for corrosion.
5. Run your VIN at nhtsa.gov/recalls.

Likely causes

1. Weak original 12V battery. Owners said the original 12V battery is weak. The 12V battery is the small battery that powers the computers, locks and screens.
2. Hands-free door kick sensors draining the battery. Kick sensors are under the rear bumper and open the power doors when you wave a foot. Owners said faulty ones drained batteries and dealers replaced them.
3. Corroded wiring to the rear AWD motor. AWD Siennas have an electric motor driving the rear wheels. One owner's dealer fixed corroded wiring, but the warning came back.
4. Hybrid battery or system fault. One owner got code P0AA6-49, which points to a high-voltage isolation fault. A commenter suggested checking the battery cells.

What it usually costs

Owners in these threads were under warranty and didn't post prices.

Is it safe to keep driving?

If a hybrid system warning is on, the van may lose power. Get it checked soon. If it won't start, it isn't safe to rely on until fixed.

DIY or shop?

Testing and charging the 12V is DIY. Kick sensors, wiring and hybrid faults are dealer work, ideally under warranty.

Recalls, bulletins and complaints in plain words

• Recalls: NHTSA's recall and complaint lookups for the 2021-2025 Sienna returned errors on 2026-11-03, so no recall or complaint data came back. That doesn't mean there are none. Run your VIN at nhtsa.gov/recalls.
• Plain words: NHTSA's complaint lookups for the 2021-2025 Sienna returned errors on 2026-11-03, so the count below is zero only because no data came back.
• NHTSA complaints: 0 keyword-matched complaints for Toyota Sienna 2021–2025 (of 0 unique complaints queried, NHTSA complaints API by model year, queried 2026-11-03; keywords: hybrid system, check hybrid, 12 v, dead, won t start, warning, loss of power, lost power, stall) (NHTSA returned no data for 10 model-year queries). This counts complaints that mention these words. It is not a defect finding.

What owners report

• In 2025 toyota sienna hybrid system malfunction on Reddit r/ToyotaSienna, a 2025 Sienna owner got hybrid system warnings. The dealer fixed corroded AWD wiring, but the problem came back and it was on its fourth dealer visit with code P0AA6-49. A reply suggested a bad cell and checking with a hybrid battery app.
• In 2025 Sienna Hybrid Battery Issued on Reddit r/ToyotaSienna, a 2025 Sienna XSE was dead within 12 hours of parking. Replies said faulty kick sensors had drained other owners' batteries and were replaced, and that the original 12V is weak. The owner said it still died with kick sensors and power doors turned off.

Quick tip

Keep a jump pack, document every event, and push for a full diagnosis on repeat visits.

Vehicle focus: Toyota Sienna hybrid, 2021-2025.

Safety / mechanic note

Loss of power is dangerous in traffic. A hybrid's high-voltage system can stay live with the car off. Leave the orange cables and the big battery to a trained technician. Verify with a mechanic.