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 283 (ENGINE CONTROLS - TROUBLESHOOTING - NO CODES)SYMPTOMSHARD STARTSENSOR/SYSTEM
1999 GMC Forward Control 5.7 R, Automatic
Hard Start: Sensor/System
1999 GMC Forward Control 5.7 R, AutomaticSECTION Sensor/System
WARNING: This page is about a different car, the 2003 Cadillac Seville and 2003 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.
- Inspect the Engine Coolant Temperature (ECT) sensor for being shifted in value. Install the scan tool and compare the displayed engine coolant temperature with the intake air temperature on a cold engine. Check the resistance of the ECT sensor if the engine coolant temperature is not within 5°F of Intake Air Temperature (IAT). See TEMPERATURE VS RESISTANCE table. If the ECT sensor resistance is not within the specification, see DTC P0117: ECT SENSOR CIRCUIT -- LOW VOLTAGE or DTC P0118: ECT SENSOR CIRCUIT -- HIGH VOLTAGE under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - 4.6L DEVILLE & SEVILLE article.
- Inspect Mass Air Flow (MAF) sensor and connections.
- Inspect the operation of the Idle Air Control (IAC) valve. See IDLE AIR CONTROL SYSTEM DIAGNOSIS under IDLE CONTROL SYSTEMS in SYSTEM & COMPONENT TESTING - 4.6L DEVILLE & SEVILLE article.
- Using the scan tool, monitor the Throttle Position (TP) sensor voltage. The TP sensor voltage should be less than 0.9 volts with a closed throttle. If the TP sensor voltage is more than 0.9 volts, inspect the throttle body and accelerator cables for binding.
- Inspect for the proper operation of the Exhaust Gas Recirculation (EGR) system. See EXHAUST GAS RECIRCULATION under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 4.6L DEVILLE & SEVILLE article.
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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.