Loss-of-communication U-codes can set for a variety of reasons. Many times, they're transparent to the vehicle operator and technician, and/or have no associated symptoms. They will eventually erase themselves automatically after a number of fault-free ignition cycles. Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Additionally, a loss-of-communication U-code does not typically represent a failure of the module that set it. The most likely scenario of this condition would be attributed to:
- A control module on the data communication circuit was disconnected while the communication circuit is awake
- Power to one or more modules was interrupted during diagnosis
- A low battery condition was present, so some control modules stop communicating when battery voltage drops below a certain threshold
- Battery power was restored to the vehicle and all control modules on the communication circuit did not re-initialize at the same time
If a loss of communication U-code appears in history for no apparent reason, it is most likely associated to the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault causing part replacement.
TIP: A loss-of-communication U-code does not typically represent a failure of the module that set it.
It's important to remember that all "current" or "active" DTCs need to be diagnosed and repaired by following proper service procedures. Always remember to clear all DTCs after successfully diagnosing and repairing a customer concern.
- Thanks to Paul Gallo
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