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 143 (AUTOMATIC TRANSAXLE DIAGNOSIS - 4T65-E)SELF-DIAGNOSTIC SYSTEMDIAGNOSTIC TROUBLE CODE DEFINITIONS
1999 GMC Forward Control 5.7 R, Automatic
Diagnostic Trouble Code Definitions
1999 GMC Forward Control 5.7 R, AutomaticSECTION Diagnostic Trouble Code Definitions
WARNING: This page is about a different car, the 2003 Buick Regal and 2003 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
Only transaxle-related DTCs are listed. For engine-related DTC definitions, see appropriate SELF-DIAGNOSTICS article in ENGINE PERFORMANCE. These DTCs pertain to engine performance and must be repaired first, as engine performance and related component signals will affect transaxle operation and diagnosis.
DIAGNOSTIC TROUBLE CODE DEFINITIONS (1)
| DTC | Circuit & Fault Definition | ||
|---|---|---|---|
| P0218 | Transaxle Fluid Overtemperature | ||
| P0502 | VSS Low Input | ||
| P0503 | VSS Circuit Performance | ||
| P0711 | TFT Sensor Circuit Performance | ||
| P0712 | TFT Sensor Circuit Low Input | ||
| P0713 | TFT Sensor Circuit High Input | ||
| P0716 | ISS Circuit Performance | ||
| P0717 | ISS Circuit No Signal | ||
| P0719 | TCC Brake Switch Circuit Low Input | ||
| P0724 | TCC Brake Switch Circuit High Input | ||
| P0730 | Incorrect Gear Ratio | ||
| P0741 | TCC System Stuck Off | ||
| P0742 | TCC System Stuck On | ||
| P0748 | Pressure Control Solenoid Electrical Problem | ||
| P0751 | 1-2 Shift Solenoid Performance | ||
| P0752 | 1-2 Shift Solenoid Performance | ||
| P0753 | 1-2 Shift Solenoid Electrical Problem | ||
| P0756 | 2-3 Shift Solenoid Performance | ||
| P0757 | Shift Solenoid Valve Performance | ||
| P0758 | 2-3 Shift Solenoid Electrical Problem | ||
| P1811 | Maximum Adapt & Long Shift | ||
| P1814 | Torque Converter Overstress | ||
| P1819 | Internal Mode Switch - No Start Wrong Range | ||
| P1820 | Internal Mode Switch Circuit A - Low | ||
| P1822 | Internal Mode Switch Circuit B - High | ||
| P1823 | Internal Mode Switch Circuit P - Low | ||
| P1825 | Internal Mode Switch - Illegal Range | ||
| P1826 | Internal Mode Switch Circuit C - High | ||
| P1860 | TCC PWM Solenoid Electrical Problem | ||
| P1887 | TCC Release Switch Circuit 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.