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.
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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 638 (DATA LINK COMMUNICATION SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESDTC U1000 AND U1255: OPERATING PARAMETER HAS NOT BEEN ASSOCIATEDTEST DESCRIPTION
1999 GMC Forward Control 5.7 R, Automatic
Test Description
1999 GMC Forward Control 5.7 R, AutomaticSECTION Test Description
WARNING: This page is about a different car, the 2003 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.
The numbers below refer to the step numbers on the diagnostic table.
- A Lost Communication with XXX DTC with a history status may indicate the cause of U1000 or U1255.
- The modules which is not communicating is the likely cause of U1000 or U1255 being set.
- The module which was not communicating may have set Lost Communication with XXX DTCs for those modules that it was monitoring.
- The module which was not communicating may have set Lost Communication with XXX DTCs for those modules that it was monitoring.
- The module which was not communicating may have set Lost Communication with XXX DTCs for those modules that it was monitoring.
- The modules which can communicate indicate the module which cannot communicate. You must clear the DTC from these modules to avoid future misdiagnosis.
- If all modules are communicating, the module which set U1000 or U1255 may have done so due to some other condition.
- The module which set U1000 or U1255 is the likely cause of the malfunction.
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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.