Cadillac U1639
Contact General Mo
Quick answer
For a 2023 Cadillac LYRIQ in the US, DTC U1639 is documented in an official GM/NHTSA communication as potentially occurring with no communication to the Brake System Control Module. GM’s listed correction is: “Contact General Mo.”
This page separates verified manufacturer/regulator evidence from supporting material. Unsupported causes, repairs or safety conclusions are not guessed.
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1. What does U1639 mean?
For a 2023 Cadillac LYRIQ in the US, DTC U1639 is documented in an official GM/NHTSA communication as potentially occurring with no communication to the Brake System Control Module. GM’s listed correction is: “Contact General Mo.”
2. Technical explanation
The supplied official manufacturer communication, PIC6483A (published by NHTSA on February 7, 2024), states that U1639 and/or U1610 may be set and that there may be no communication with the Brake System Control Module. The communication also states that the cause was under investigation at the time of publication.
3. What system is affected?
Brake System Control Module communication is specifically identified by the verified source. A broader system designation is not yet established by verified evidence.
4. How serious is this code?
Not yet established by verified evidence. However, the verified bulletin concerns Brake System Control Module communication and mentions brake-pedal concerns, so GM contact is the documented correction.
5. Symptoms you may notice
- No communication with the Brake System Control Module.
- A hard or soft brake pedal may be reported.
- No warning chime is stated in the official communication.
6. Possible causes
- Cause under investigation, according to the official GM/NHTSA communication.
7. Can I still drive the vehicle?
Not yet established by verified evidence.
8. Can I charge the vehicle?
Not yet established by verified evidence.
9. What you can safely do
- Do not attempt high-voltage or Brake System Control Module repairs yourself.
- Arrange contact with a Cadillac/GM dealer or GM service organization, as directed by the official communication.
- Tell the service provider that U1639 is stored and report any hard or soft brake-pedal concern.
10. Step-by-step troubleshooting
- Verify whether DTC U1639 is present.
- Check for communication with the Brake System Control Module using appropriate professional diagnostic equipment.
- Check whether U1610 is also stored; the official communication identifies U1610 and/or U1639.
11. When to contact service
Yes. The official correction for this communication is: “Contact General Mo.”
12. What the service center may check
- Confirm the presence of U1639 and any accompanying U1610.
- Assess communication with the Brake System Control Module.
- Follow current GM service guidance, since the cause was under investigation in the cited communication.
13. Possible repair or resolution
- The verified communication does not provide a component-level repair procedure or final repair resolution.
- GM’s documented correction is to contact General Motors.
14. Affected vehicles
- Cadillac LYRIQ · 2023 · US
15. Related TSBs / service bulletins
- PIC6483A / NHTSA Manufacturer Communication PDF 10251686, published February 7, 2024. It applies in the supplied evidence to the 2023 Cadillac LYRIQ in the US and states that U1610 and/or U1639 may be set with no communication to the Brake System Control Module. Cause: under investigation. Correction: “Contact General Mo.”
16. Recall information
- Not yet established by verified evidence.
17. Official manufacturer information
Official source: NHTSA Manufacturer Communication PDF 10251686, GM PIC6483A: https://static.nhtsa.gov/odi/tsbs/2024/MC-10251686-9999.pdf
19. Frequently asked questions
What does U1639 mean on a 2023 Cadillac LYRIQ?
The supplied diagnostic record labels U1639 as “Contact General Mo.” The cited official GM communication associates U1639 and/or U1610 with possible loss of communication with the Brake System Control Module.
What symptoms are documented with U1639?
The official communication states that a hard or soft brake pedal may be reported, there may be no warning chime, and there may be no communication with the Brake System Control Module.
What causes U1639?
The official communication states that the cause was under investigation. A specific root cause is not yet established by verified evidence.
Can I drive with U1639?
Not yet established by verified evidence. Because the documented condition involves Brake System Control Module communication and possible brake-pedal concerns, contact Cadillac/GM service.
Is there a known repair for U1639?
A specific repair is not provided in the verified communication. Its listed correction is “Contact General Mo.”