Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
DTC U1000 Or U1255: Class 2 Communication Malfunction: Description
Serial data circuit is used to communicate information and commands between modules. When a module receives a message for a critical operating parameter, the module records the Body Control Module (BCM) number of the module which sent the message for State Of Health (SOH) monitoring.
When a module does not associate an identification number with at least one critical parameter within about 5 seconds after beginning communication, DTC will set. When more than one critical parameter does not have an identification number associated with it, DTC will only be reported once. When DTC is present, SERVICE VEHICLE SOON indicator will turn on and module will use a default value for the missing critical parameter.
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.