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)DIAGNOSTIC INFORMATION AND PROCEDURESSCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICEDIAGNOSTIC AIDS
1999 GMC Forward Control 5.7 R, Automatic
Diagnostic Aids
1999 GMC Forward Control 5.7 R, AutomaticSECTION Diagnostic Aids
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.
- An open in the ignition 1 circuit to the PCM will cause the PCM to stop communicating without setting communication DTCs. Refer to CIRCUIT TESTING and WIRING REPAIRS .
- If a short to B+ was present, a history U1301 or U1305 will set in the modules. Refer to DTC U1300, U1301, or U1305 (Generic Short DTC) .
- If a short to ground was present, a history U1300 or U1305 will set in the modules. Refer to DTC U1300, U1301, or U1305 (Generic Short DTC) .
- Disconnecting modules and turning the ignition switch to RUN may cause DTCs in these modules. Check for DTCs in each module upon completion of the required repair.
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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.