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Cadillac U1643

If the entire bus is impacted (multiple ECUs with comm loss). • Do not replace the front camera. • Diagnose the CA

DriveNot yet established by verified evidence.
ChargeNot yet established by verified evidence.
ServiceService evaluation is appropriate because the official bulletin directs diagnosis of a CAN bus concern when multiple ECUs have communication loss. Drive and charging suitability are not established by the supplied evidence.
Confidence95%

Quick answer

For applicable Cadillac EVs, U1643 is listed in GM bulletin PIT6503 revisions as a possible loss-of-communication DTC on CAN Bus 2. If multiple ECUs have communication loss across the bus, the bulletin says not to replace the B174W Front View Camera module; diagnose the CAN bus concern instead.

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 U1643 mean?

For applicable Cadillac EVs, U1643 is listed in GM bulletin PIT6503 revisions as a possible loss-of-communication DTC on CAN Bus 2. If multiple ECUs have communication loss across the bus, the bulletin says not to replace the B174W Front View Camera module; diagnose the CAN bus concern instead.

2. Technical explanation

Verified bulletin evidence instructs technicians to check whether the K56 Serial Data Gateway Module is also setting loss-of-communication DTCs against other ECUs on CAN Bus 2. U1643 is one of the example DTCs listed. Where the entire bus is affected, meaning multiple ECUs have communication loss, the specified direction is not to replace the B174W Front View Camera module and to diagnose the CAN bus concern.

3. What system is affected?

CAN Bus 2 communication network; K56 Serial Data Gateway Module and multiple ECUs may be involved. The B174W Front View Camera module is specifically identified as a component that should not be replaced when the entire bus is impacted.

4. How serious is this code?

Not yet established by verified evidence.

5. Symptoms you may notice

  • Multiple ECUs may have loss-of-communication DTCs on CAN Bus 2.
  • The K56 Serial Data Gateway Module may also set loss-of-communication DTCs against other ECUs on CAN Bus 2.

6. Possible causes

  • A CAN bus concern when the entire bus is impacted by communication loss. The verified evidence does not establish a more specific root cause.

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

  • Have the vehicle evaluated by a qualified Cadillac service facility.
  • Provide the stored DTCs and note whether multiple ECUs report communication loss.
  • Do not authorize replacement of the B174W Front View Camera module solely because the entire CAN Bus 2 network is affected.

10. Step-by-step troubleshooting

  1. Check whether the K56 Serial Data Gateway Module is also setting loss-of-communication DTCs against other ECUs on CAN Bus 2.
  2. Determine whether the concern affects the entire bus, with multiple ECUs reporting communication loss.
  3. If the entire bus is impacted, diagnose the CAN bus concern rather than replacing the B174W Front View Camera module.

11. When to contact service

Service evaluation is appropriate because the official bulletin directs diagnosis of a CAN bus concern when multiple ECUs have communication loss. Drive and charging suitability are not established by the supplied evidence.

12. What the service center may check

  • Review DTCs stored by the K56 Serial Data Gateway Module.
  • Check for loss-of-communication DTCs against other ECUs on CAN Bus 2.
  • Assess whether multiple ECUs are affected across the entire bus.
  • Follow CAN bus diagnostic procedures if the entire bus is impacted.

13. Possible repair or resolution

  • Do not replace the B174W Front View Camera module when the entire bus is impacted by multiple ECU communication losses.
  • Diagnose the CAN bus concern. No specific repair is established by the supplied verified evidence.

14. Affected vehicles

15. Related TSBs / service bulletins

  • GM PIT6503C, published August 12, 2026; NHTSA Manufacturer Communication PDF 11036219: https://static.nhtsa.gov/odi/tsbs/2026/MC-11036219-0001.pdf
  • GM PIT6503B, published June 17, 2026; NHTSA Manufacturer Communication PDF 11034014: https://static.nhtsa.gov/odi/tsbs/2026/MC-11034014-0001.pdf
  • GM PIT6503A, published June 3, 2026; NHTSA Manufacturer Communication PDF 11033726: https://static.nhtsa.gov/odi/tsbs/2026/MC-11033726-0001.pdf
  • GM PIT6503, published April 14, 2026; NHTSA Manufacturer Communication PDF 11031514: https://static.nhtsa.gov/odi/tsbs/2026/MC-11031514-0001.pdf

16. Recall information

  • Not yet established by verified evidence.

17. Official manufacturer information

The supplied official NHTSA-hosted manufacturer communications identify U1643 as an example CAN Bus 2 loss-of-communication DTC and provide the diagnostic direction for an entire-bus communication-loss condition.

19. Frequently asked questions

Does U1643 mean the front camera must be replaced?

No, not when the entire CAN Bus 2 network is impacted and multiple ECUs have communication loss. The bulletin specifically says not to replace the B174W Front View Camera module in that situation.

What should be checked with U1643?

The bulletin directs checking whether the K56 Serial Data Gateway Module also has loss-of-communication DTCs against other ECUs on CAN Bus 2, then determining whether multiple ECUs are affected.

Which vehicles are covered by the supplied applicability data?

US-market Cadillac CELESTIQ model years 2024–2026; LYRIQ model years 2024–2026, with an additional 2024–2025 applicability record; OPTIQ model years 2024–2026; and VISTIQ model years 2024–2026.

Is it safe to drive or charge with U1643?

Not yet established by verified evidence.

20. Sources & verification

Verified
Cadillac U1643: If the entire bus is impacted (multiple ECUs with comm… | EV Diagnostics