Why does my Chevy Volt say 'Service High Voltage Charging System' and won't charge?

Short answer: On a Volt, this message usually means the battery coolant is low, the coolant level sensor has failed, or the battery and charging computers need GM's updated software. Check the battery coolant tank first. If the message keeps coming back, ask a dealer to do the service bulletin reprogramming of the BECM and HPCM2.

Symptom: The 'Service High Voltage Charging System' message appears, the check engine light may be on, and the car won't take a plug-in charge until the codes are cleared. The car still drives on gas.

What to check first

1. Look at the battery coolant tank (not the engine or washer tank) with the car off and cool. Top it up only with the coolant your manual lists.
2. Have the codes read with a tool that can see the hybrid modules. A cheap reader may only show a generic code.
3. Ask the dealer about GM's service bulletin for this message and whether the BECM and HPCM2 have the latest software.
4. If you use an app like MyVoltControl, check the high-voltage isolation reading.
5. Run your VIN at nhtsa.gov/recalls.

Likely causes

1. Battery coolant low or the coolant level sensor. The big battery has its own coolant tank. If it's low, or the small level sensor in that tank goes bad, the car blocks charging. Several owners found the tank a couple of inches low.
2. Module software needs reprogramming (BECM and HPCM2). The BECM (battery energy control module) and HPCM2 (hybrid powertrain control module 2) are the computers that run the big battery and charging. Owners said that once this message sets, it keeps coming back until both modules get GM's updated software, which a service bulletin covers.
3. Low battery isolation reading. Isolation is a safety check that the high-voltage system isn't leaking current to the car's body. One owner's app showed a low isolation reading that cleared after the software update.
4. A real fault in the charging hardware. If coolant, sensor and software are all good and the message returns after every charge, a dealer with Volt experience needs to dig deeper.

What it usually costs

Owners paid $85 at one dealer and $175 per module at another for the programming. One paid about $288 CAD for the leak check and updates, and a 2014 owner paid a little over $500 for a new coolant level sensor and harness. One dealer asked $1,000 just to diagnose, and owners said to shop around.

Is it safe to keep driving?

Yes. The car still drives on gas, but you lose plug-in charging. Don't keep driving with a low battery coolant level for long, and get the message checked.

DIY or shop?

Checking and topping up the battery coolant is DIY. Reprogramming is mostly a dealer job. Some owners did it themselves with a VCX Nano and a paid GM software subscription, but it's not for beginners.

Recalls, bulletins and complaints in plain words

• Recalls: NHTSA lists recall 18V397000 for certain 2013 Volts: an earlier HPCM2 software update could turn off cell balancing and cause a low-voltage condition in the big battery. It's not the same as this message, but it involves the same module. NHTSA's recall lookup returned errors for 2014 and 2017, so 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's recall lookup returned errors for 2014 and 2017.
• NHTSA complaints: 344 keyword-matched complaints for Chevrolet Volt 2011–2019 (of 1874 unique complaints queried, NHTSA complaints API by model year, queried 2026-11-04; keywords: charging, charge, high voltage, coolant, won t charge, service high, plug) (NHTSA returned no data for 2 model-year queries). This counts complaints that mention these words. It is not a defect finding.

What owners report

• In Service High Voltage Charging System on Reddit r/volt, an owner's Volt refused to charge and the battery coolant was a couple of inches low. Topping it off and clearing the codes didn't last. Replies said the codes come back until the modules are reprogrammed, and one owner who accidentally opened the battery coolant cap had the dealer reset it and update the software for free.
• In Service High Voltage Charging System? on Reddit r/volt, owners said to fill the battery coolant with the correct ACDelco coolant first, then have the two modules reprogrammed, because a cheap code reader only clears it for a day or two. One owner whose app showed low battery isolation paid about $288 CAD for the bulletin's leak check and module updates and had no trouble after.
• In Service High Voltage Charging System on Reddit r/volt, a 2013 owner had to clear the message after every charge, and the dealer wanted $1,000 just to diagnose it. Other owners said the real fix was the software update on the HPCM2 and related modules (one paid $175 per module programmed), another's dealer topped up low coolant and it never came back, and a 2014 owner paid a little over $500 for a new coolant level sensor and harness.
• In Fixed my Chevy Volt Service High Voltage Charging System Error and This is what I learned on Reddit r/volt, an owner fixed the message for good by reprogramming the BECM and HPCM2 himself with a VCX Nano tool and an ACDelco software subscription, after a sensor bypass plug alone didn't work. He warned the process was tricky and he briefly thought he'd bricked the car. Another owner's dealer charged $85 for the programming.

Quick tip

Check the battery coolant, then push the dealer for the bulletin's software update instead of paying for a long diagnosis. Clearing codes is only a stopgap.

Vehicle focus: Chevrolet Volt plug-in hybrid, 2011-2019 (most reports are first-generation 2011-2015 cars).

Safety / mechanic note

Never open the battery coolant tank while hot, and only use the coolant your manual lists. An EV's or plug-in hybrid's high-voltage system can stay live with the car off. Leave the orange cables, the big battery and the charging hardware to a trained technician. Verify with a mechanic.