My Cadillac Lyriq says "Service High Voltage System." What does that mean?

Short answer: On a Lyriq, Service High Voltage System doesn't always mean the big battery is bad. One owner's 12-volt was being drained by software updates that kept failing, and the dealer fixed it by installing the updates and recharging the battery. Others had charging or high-voltage faults that needed the dealer, especially on cold mornings. Install pending updates, keep the 12-volt charged, and book service if the message comes back.

Symptom: 'Service High Voltage System' or 'Service Vehicle' messages, app alerts for the high-voltage battery or onboard charger, a car that won't charge, or an OnStar warning that the 12-volt is low.

What to check first

1. Check for pending software updates and let them finish while you're nearby.
2. If OnStar or the app says the 12-volt is low, get it charged and tested.
3. Note the outside temperature and what you were doing (charging, just parked) when it happened.
4. If it won't charge, try a different charger once, then call the dealer.
5. Run your VIN at nhtsa.gov/recalls.

Likely causes

1. 12-volt battery drained (often by failed software updates). Almost every modern car, including EVs and hybrids, has a small 12-volt battery that powers the computers, locks and screens. When it's weak, the car can show a pile of unrelated warnings or refuse to go into gear, even with a full main battery. One owner's updates kept failing mid-download every time they parked, which drained it.
2. High-voltage battery or onboard charger fault. The onboard charger is the part inside the car that turns wall power into battery power. A fault there can stop charging altogether.
3. Software glitch that clears with a reset. Some owners clear the warning by fully disconnecting the 12-volt battery for a while. It's a temporary fix, not a repair.

What it usually costs

Owners in these threads had it handled under warranty and didn't post prices.

Is it safe to keep driving?

If the car drives normally and the message clears, owners booked service. If you get reduced power, it won't charge, or it won't go into drive, call Cadillac roadside instead of driving far on what's left.

DIY or shop?

Keeping the 12-volt charged and installing updates is DIY. Owners say disconnecting the 12-volt is a temporary reset, but on a new car let the dealer find the cause so it's on record. An EV's high-voltage system can stay live with the car off. Leave the orange cables, the big battery and the drive unit to a trained EV technician.

Recalls, bulletins and complaints in plain words

• Related recalls: NHTSA lists 23V367000 for some 2023 Lyriqs: connections in the high-voltage battery pack may be out of position or badly welded, which can cause loss of drive power. It also lists 24V320000 for some 2024 models (rear drive motor wiring), 25V483000 for some 2025 models (bolts holding the high-voltage battery may be loose or missing), and 22V710000 and 25V356000 (the driver display can go blank). Check your VIN at nhtsa.gov/recalls. If your car is part of a recall, the dealer fixes it for free.
• Plain words: The complaint count below shows how often owners reported problems that mention these words to NHTSA. A count is not proof of a defect.
• NHTSA complaints: 25 keyword-matched complaints for Cadillac Lyriq 2023–2025 (of 159 unique complaints queried, NHTSA complaints API by model year, queried 2026-10-31; keywords: high voltage, 12 v, battery, charg, won t start, dead). This counts complaints that mention these words. It is not a defect finding.

What owners report

• In 12V battery drained by software updates on Reddit r/CadillacLyriq, a Lyriq owner got the Service High Voltage System message, then OnStar warned the 12-volt was low. The dealer found that software updates were failing mid-download every time the car parked, draining the 12-volt. The dealer ran the updates, recharged the battery and said it tested healthy, all under warranty.
• In Picked up my 2026 LYRIQ today – already getting High Voltage Battery & Onboard Charging System errors on Reddit r/CadillacLyriq, a 2026 Lyriq showed high-voltage battery, onboard charging and battery conditioning faults on day one and wouldn't charge. A commenter explained disconnecting the 12-volt as a temporary reset and said to let the car shut down fully before reconnecting. Another owner said their 2024 Lyriq was at the dealer after the fault came back on a dozen frigid mornings in January.

Quick tip

Get it on record. Even if a reset makes it go away, call the dealer so the fault is documented while it's under warranty.

Vehicle focus: Cadillac Lyriq, 2023-2026 (NHTSA data below covers 2023-2025).

Safety / mechanic note

Loss of drive power and high-voltage faults are safety items. Verify with a mechanic.