A U code indicates a communication loss on the BUS. Start by performing a hard battery reset (instructions are below). If that doesn't resolve the issue, inspect the connectors for bent pins and check all vehicle fuses. Any loss of power can lead to communication problems.
Hard Battery Reset Procedure:
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Disconnect the battery cables.
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Clamp the cables together with the terminals touching (off the battery!)
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Leave the cables maintained in this position for 30min. and then re-install.
HELPFUL TIP
Whenever doing a hard reset (global reset) always remove the ground cable first then the positive cable. When reinstalling a battery or just the cables install positive first then attach the ground. It's always best to do it this way so there are almost no issues causing an electrical spark on a module in the vehicle.
*This should clear any soft codes and communication issues with the vehicle’s PCI bus.*
If the light is on, then it will be best to scan for codes.
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