2017-2018 Cadillac CT6 Plug-In HV Battery: Decoding Failures and Replacement
This is the definitive guide to the high-voltage (HV) drive battery for the rare 2017-2018 Cadillac CT6 Plug-In Hybrid, not the common 12-volt battery.
- This is the high-voltage (HV) battery for the 2017-2018 CT6 Plug-In Hybrid (PHEV) ONLY, not the standard 12V battery.
- Replacement is NOT a DIY job. It requires certified technicians, special lifting tools loaned from GM, and vehicle-specific programming.
- A common failure symptom is the "Service High Voltage Charging System" message, which can be caused by the battery itself or a low coolant level in its dedicated cooling system.
- GM placed this battery on a restriction program (TSB PIC6272B), meaning dealers must get authorization from a technical hotline before ordering a replacement, which can complicate and delay repairs.
Critical Compatibility Warning
This is the main high-voltage (HV) drive battery for the 2017-2018 Cadillac CT6 Plug-In Hybrid (PHEV) model ONLY. It is NOT the standard 12-volt battery used for starting the engine and running accessories. This part will NOT fit gasoline-only (non-hybrid) vehicles. Attempting to install this in a non-PHEV model is impossible and dangerous.
Symptoms of a Failing High-Voltage Battery
A failing HV battery in the CT6 PHEV will present several distinct symptoms, many of which are communicated through the driver information center.
- "Service High Voltage Charging System" Message: This is the most common and direct indicator of a problem within the HV system. While it can point to the battery itself, it is often triggered by issues in related components, such as a faulty battery coolant level sensor. One owner noted this message can appear if the battery coolant level is even slightly low, as it can ingest air bubbles. This message will often prevent the vehicle from charging.
- Significantly Reduced Electric Range: One of the first noticeable symptoms is a drop in the all-electric miles you get from a full charge. While some degradation is normal over time, a sudden or severe drop indicates failing cells within the battery pack.
- Inability to Hold a Charge: The battery may appear to charge fully, but the stored energy depletes much faster than normal, or it may not charge at all.
- Dead 12-Volt Battery: A failing HV battery system can sometimes create a parasitic drain on the vehicle's conventional 12V battery, causing it to go dead unexpectedly. A GM technical bulletin notes this can occur with a drain between 200mA and 1500mA.
- Diagnostic Trouble Codes (DTCs): Specific codes stored in the vehicle's computer can pinpoint the issue. Common codes associated with these symptoms include P1E00 and P2535.
Known Issues, TSBs, and Recalls
While no major safety recalls exist for the 2017-2018 CT6 PHEV's high-voltage battery specifically, several Technical Service Bulletins (TSBs) provide important context for owners and technicians.
TSB PIC6272B: High-Voltage Battery Placed on Restriction
This is the most significant bulletin for this part. As of May 2017, GM placed the CT6 PHEV drive motor battery and its internal components on restriction. This means a dealership cannot simply order a replacement. They must first call the General Motors Technical Assistance Center (TAC) to get authorization. This process was implemented for quality control and to allow GM engineers to gather data on failed units. This procedure can add time and complexity to the repair process.
Other Relevant Bulletins
- TSB 18-NA-180: A bulletin that outlines the official warranty exchange process for lithium-ion batteries.
- Preliminary Information Bulletin PIC6076: Addresses the "Service High Voltage Charging System" message and associated DTC P1E.
- Parasitic Drain Bulletin: An unnumbered preliminary bulletin discusses a potential parasitic draw that depletes both the HV and 12V batteries, sometimes logging DTC P2535.
Pro Tip: An owner on an online forum discovered that keeping the high-voltage battery coolant reservoir filled slightly above the 'full' line (the center seam of the tank) can prevent the "Service High Voltage Charging System" error caused by air bubbles entering the sensor.
Buying a Used 2017-2018 CT6 High-Voltage Battery
Due to the extremely high cost of a new battery, a used OEM unit can offer significant savings. However, purchasing a used HV battery carries risks. Here’s what to check before you buy.
1. Supplier Reputation
Buy only from a reputable, professional auto recycler that specializes in hybrid and electric vehicles. Ask if they tested the battery or can provide any information from the donor vehicle, such as mileage and whether it had any error codes present before being dismantled.
2. Physical Inspection
If you can inspect the battery before purchase, look for:
- No Physical Damage: The outer case should be free of cracks, dents, or punctures. Damage can indicate internal cell damage.
- No Leaks: Check for any signs of coolant leakage. The battery has its own cooling circuit, and a leak is a critical failure.
- Clean Connectors: All high-voltage and data connectors should be clean, dry, and free of corrosion or arcing marks.
3. Donor Vehicle History
The two most important factors for a used battery's health are mileage and climate.
- Mileage: Lower mileage is always better. A battery with 50,000 miles will have significantly more life left than one with 150,000 miles.
- Climate: A battery that spent its life in a hot climate (like Arizona or Texas) will have degraded faster than one from a mild climate (like the Pacific Northwest). Heat is the primary enemy of lithium-ion battery longevity. Ask for the donor vehicle's VIN to check its history.
4. Part Number Verification
Ensure the part number on the used battery matches one of the known OEM numbers for your vehicle. Do not rely on visual similarity alone.
Replacement Procedure and Difficulty
Danger: High Voltage Kills. This is not a DIY job. The battery pack operates at over 350 volts, which can be lethal. Replacement must be performed by a certified technician with specific training in high-voltage systems and the proper personal protective equipment (PPE).
- Installation Difficulty: 5 out of 5 (Professional Only)
- Procedure: The battery is installed from underneath the vehicle. It requires special lifting equipment, including the EL-51865 Battery Pack Support Fixture, which is part of a GM loaner tool program available only to dealers and certified shops.
- Programming Required: After installation, a new battery must be programmed to the vehicle. This involves procedures like a "battery pack capacity learn" using GM's diagnostic software. A used battery will also require this programming to ensure it communicates correctly with the vehicle's control modules.
Cost of Replacement
Replacing the HV battery is a significant expense. The primary benefit of a used OEM part is the substantial cost savings over a new unit.
| Part Type | Estimated Cost |
|---|---|
| New OEM | $6,600 - $8,600 |
| Remanufactured OEM | $3,000 - $5,000 (Varies by supplier) |
| Used OEM | $2,000 - $4,000 (Varies by mileage and condition) |
| New Aftermarket | Not Available |
| Shop Labor | $800 - $1,500+ |
Frequently Asked Questions (FAQ)
Can I use a battery from a Chevy Volt?
No. Although the CT6 PHEV uses technology derived from the GM Voltec system, the battery pack's physical shape, size, and specific programming are unique to the CT6. You must use a battery pack specifically designed for the 2017-2018 CT6 Plug-In Hybrid.
Is there a core charge for this battery?
Yes. When purchasing a new or remanufactured battery from a dealer, there is a substantial core charge that is refunded when the old battery is returned. GM has a very strict return process, requiring the old battery to be shipped back in the special 'cocoon' container the new one arrived in. This process may be difficult or impossible to navigate for a private individual, making a used part more straightforward.
What is the difference between the HV battery and the 12V battery?
The High-Voltage (HV) battery is a large, powerful lithium-ion pack that powers the electric motors to move the car. The 12V battery is a conventional, smaller battery (similar to what's in a non-hybrid car) located in the trunk that powers the lights, radio, computers, and accessories, and is essential for starting the car's systems.
Does the battery have its own cooling system?
Yes. The CT6 PHEV has three separate cooling systems, and one is dedicated entirely to managing the temperature of the high-voltage battery pack. Maintaining this system and its coolant level is critical to the battery's health and function.
Technical Specifications
OEM Part Numbers: 24062816 24284826 24284850 24290892 24291888
Type: Lithium-Ion | Capacity: 18.4 kWh | Nominal Voltage: 355V DC | Cell Configuration: 192 prismatic pouch cells in 96 series groups | Location: Behind the rear seat
The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
- Cadillac CT6:
- Critical Compatibility Warning
- Symptoms of a Failing High-Voltage Battery
- Known Issues, TSBs, and Recalls
- TSB PIC6272B: High-Voltage Battery Placed on Restriction
- Other Relevant Bulletins
- Buying a Used 2017-2018 CT6 High-Voltage Battery
- 1. Supplier Reputation
- 2. Physical Inspection
- 3. Donor Vehicle History
- 4. Part Number Verification
- Replacement Procedure and Difficulty
- Cost of Replacement
- Frequently Asked Questions (FAQ)
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