Practical checks and shop questions for U-codes and multi-warning events; save evidence before replacing parts.
This is a non-invasive owner checklist, not an OEM repair procedure or permission to drive.
This reference supports the stated topic only. Model, model year, equipment, current rule or individual vehicle conditions may differ; check the original source before acting.
Read the General Motors original: 18-NA-270 Source date: 2019-02; research checked: 2026-11-01.
Codes in this diagnostic topic
These codes share a system-level checklist, but their distinct numbers and meanings are shown below. A code here does not prove a particular vehicle has every listed fault. Use the exact code row and full scan.
| Code | Meaning | Vehicle scope |
|---|---|---|
| U0073 | Communication bus A offline | Exact vehicle scope unverified |
| U0100 | Engine/powertrain module communication lost | Exact vehicle scope unverified |
| U0101 | Transmission module communication lost | Exact vehicle scope unverified |
| U0121 | Brake-control module communication lost | Exact vehicle scope unverified |
| U0128 | Parking-brake module communication lost | Exact vehicle scope unverified |
| U0140 | Body-control module communication lost | Exact vehicle scope unverified |
Save the evidence first
- Full-system scan with reporting module
- Which modules are actually reachable
- Power interruption/recent battery work
- Heat, turn or startup timing
Safe owner checks
- Record every warning and whether braking/steering or propulsion is affected.
- Do not unplug random modules to make communication codes disappear.
Questions for a qualified technician
- Are supply, grounds, wiring damage, network integrity or calibration causing the fault?
- For Camaro LT1, does harness-contact inspection match the bulletin?
- For F-150, does U3012:68 require the documented software branch?
Common wrong turns
- A lost-communication code does not prove the named module is bad.
- Do not test a CAN/SRS/HV circuit with generic probing instructions.
Confirm the repair
- Check module communication and the original symptom, not just code deletion.
Sources and scope
- General Motors — 18-NA-270 Document: 2019-02 · Research checked: 2026-11-01
- Subaru — 09-128-24R Document: 2024-11-14 · Research checked: 2026-11-01
- Ford — 25-2245 Document: 2025-06-03 · 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.