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 839 (DATA LINK COMMUNICATIONS)
1999 GMC Forward Control 5.7 R, Automatic
Section 839 (Data Link Communications)
1999 GMC Forward Control 5.7 R, AutomaticSECTION Section 839 (Data Link Communications)
WARNING: This page is about a different car, the 2003 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
- Schematic and Routing Diagrams
- Component Locator
- Diagnostic Information and Procedures
- Diagnostic Starting Point - Data Link Communications
- Diagnostic Trouble Code (DTC) List
- DTC U1000: Critical Operating Parameter Has Not Been Associated With A Modules Assigned Id Number
- DTC U1001 to U1254: Module U1XXX Communication
- DTC U1300, U1301, or U1305: Class 2 Serial Data Circuit Voltage
- DTC U2100: Module CAN Communication Error
- DTC U2102 or U2103: Controller Count Mismatch
- DTC U2104: Module CAN Communication Error
- DTC U2105, U2106, U2107, U2108: Module CAN Communication Error
- Symptoms - Data Link Communications
- Scan Tool Does Not Power Up
- Scan Tool Does Not Communicate with Class 2 Device
- Scan Tool Does Not Communicate with Keyword Data Line
- Description and Operation
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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.