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Q: 5mph max in 40 miles & code U3107

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We have a 2014 Ram 3500 and it has a message saying 5mph max in X amount of miles we plugged in a code reader and it's throwing the code U3107. The nearest dealer is 100+ miles away on my way home it flashed off and about 50 miles later it came back. Is it driveable?

My car has 37895 miles.
My car has an automatic transmission.

A: Diagnostic Trouble Code U3107 refers to a f...

Diagnostic Trouble Code U3107 refers to a fault in the vehicle's network communications system, which includes the controller area network (CAN) wiring bus and modules on the vehicle. Unless other warning lights are on and/or the check engine light is flashing (as opposed to "steady") you can drive the vehicle. A flashing check engine light often means the engine is misfiring and that is one circumstance in which you do need to stop the engine reasonably quickly.

There are some general causes that would set Code U3107 but to get to the root issue a CAN capable scanner has to be used that can get associated freeze frame data. U3107 can set if certain CAN module connections are faulty, if there is a short to ground, an open, or voltage is below specifications. If the battery is dead, modules will lose settings or locations thus setting this code. In that event, relearning, or "re-set" procedures require a factory scan tool or a professional level aftermarket scan tool. You might try erasing the code and see if it recurs. You have referred to limp mode in your question which raises the possibility of, for example, loss of communication between modules such as an engine controller or transmission controller. You can perform a quick check of the soundness of connections at each CAN module by checking for voltage at the module, a good ground, and finally the data line. If all three check out but the module is reported by the scan tool as not communicating, the module needs will typically be replaced. YourMechanic can dispatch a professional with the appropriate check engine light diagnostic tools to identify the root cause of Code U3107 and resolve the issue for you. Please let us know if we can assist you with such a mobile visit.

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