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 813 (DATA LINK COMMUNICATION SYSTEM)
1999 GMC Forward Control 5.7 R, Automatic
Section 813 (Data Link Communication System)
1999 GMC Forward Control 5.7 R, AutomaticSECTION Section 813 (Data Link Communication System)
WARNING: This page is about a different car, the 2002 Pontiac Grand Prix. However, it is still accessible from the selected car via links, so may be relevant.
- Specifications
- Schematic and Routing Diagrams
- Component Locator
- Diagnostic Information and Procedures
- Diagnostic Starting Point - Data Link Communications
- DTC U1000 and U1255: Operating Parameter Has Not Been Associated
- DTC U1001 to U1254: Module U1XXX Communication
- DTC U1300, U1301, or U1305 (Generic Short DTC): No Valid Messages Are Detected On The Class 2 Serial Data Circuit
- DTC U1304: PCM To EBCM Communication
- 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 UART Data Line
- Repair Instructions
- 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.