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 724 (ANTILOCK BRAKE SYSTEM, TRACTION CONTROL SYSTEM & STABILITY CONTROL SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESDTC C1255 OR C1256DIAGNOSTIC 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 2004 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.
- The scan tool displays 2 additional characters after the DTC. Take note of the 2 character code and any other DTCs that are set. The 2 character code is an engineering aid used in order to determine the cause of the internal malfunction.
- When the scan tool displays DTC C1255m3, the EBCM has not been programmed. Perform the setup procedure for the EBCM.
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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.