GM Ultium isolation and thermal-priority codes: specialist escalation before parts: Source-Scope Research

What prompted this manufacturer document

• High-priority battery DTCs
• Possible no-start, abnormal noises or loss of propulsion
• This bulletin is a specialist handling/data-collection protocol, not a list of guaranteed bad battery parts or universal definitions for its U-codes.

Which vehicle conditions must be checked

Each row below retains its own conditions. Do not combine engines, years or models across rows to create new applications. A listed model is not proof that a particular VIN is affected.

• BrightDrop Zevo 600 · 2022, 2023, 2024 · BEV
• BrightDrop Zevo 400 · 2024 · BEV
• Cadillac LYRIQ · 2023, 2024 · BEV
• Chevrolet Blazer EV · 2024 · BEV
• Chevrolet Equinox EV · 2024 · BEV
• Chevrolet Silverado EV · 2024 · BEV
• GMC HUMMER EV · 2022, 2023, 2024 · BEV
• GMC HUMMER EV SUV · 2024 · BEV

Codes recorded in this document

A root listed only as an appearance has no separately verified meaning here. Preserve every suffix and module name; a shared root does not transfer a repair branch to another vehicle.

What an owner can record safely

• Whether propulsion was lost or unusual sounds occurred
• Photos of dashboard messages from a safe location
• Previous coolant addition or battery work

Editorial safety boundary for this system

Do not continue driving with loss-of-propulsion, isolation or serious battery warnings; obtain model-specific roadside guidance.

• Use current model-specific service information, calibrated equipment and a qualified technician for the selected diagnostic branch.
• Do not open the traction pack, touch orange cables or damaged connectors, bypass interlocks, or perform home insulation testing.

This is a conservative editorial policy, not a manufacturer safe-to-drive decision for a specific vehicle.

What the source does not prove

• Do not open the pack, perform owner-level insulation testing, or describe every listed communication code as a proven coolant leak.
• A code or message alone does not establish a failed part, a safe-to-drive decision or an approved repair for this VIN.
• A service bulletin is not automatically a recall or free warranty repair. Confirm current eligibility directly.

Questions for the repair shop

• Which current manufacturer procedure, VIN/RPO/build gate and test result determine the diagnostic branch?
• Does a later revision or a current recall change the source's original advice?
• What measurement or inspection confirms the cause, and how will the repair be verified?

Open source-review issue

• Q3-08: Many U-codes are listed as escalation triggers, without individual definitions. Index as appearance-only. Do not label each as a particular component failure or coolant leak.

The uncertain field is not used here to claim a current fitment, repair or market-wide failure.

Read the original record

The linked communication may be revised after the research date. Compare its document number, exact vehicle table, diagnostic preconditions and exclusions with a qualified technician. This page paraphrases selected facts and does not reproduce the manufacturer procedure.

Related reading

Sources and scope

1. General Motors — EV battery isolation and coolant-loss data collection (23-NA-151) Document: date not recorded · Research checked: 2026-11-01

Research snapshot: 2026-11-01. Source documents may have newer revisions. Verify current instructions and VIN eligibility with the manufacturer.