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How do I fix a U1900 code?
The most common cause of the trouble code U1900 is a possible defective instrument cluster or an issue with the trailer brake controller, the other possibilities are below, if you need I can send test procedures in order to determine the cause.
The high speed CAN (Controller Area Network) has an unshielded twisted pair cable, circuits 1908 (WH) and 1909 (BK). The anti-lock brake system (ABS) module, the instrument cluster, the power train control module (PCM) and the trailer brake controller are all on the CAN. The total resistance values from the module to the data link connector (DLC) must not be more than 5 ohms. If the resistance is more than 5 ohms there is an open in one of the CAN circuits, damage to the DLC C251, damage to one of the communications network module connectors, or damage to an in-line connector.
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