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 263 (ENGINE CONTROLS - SYSTEM TESTING & ENGINE COMPONENT TESTS - 3.1L)SENSORS & SWITCHESINTAKE AIR TEMPERATURE SENSOR
1999 GMC Forward Control 5.7 R, Automatic
Intake Air Temperature Sensor
1999 GMC Forward Control 5.7 R, AutomaticSECTION Intake Air Temperature Sensor
WARNING: This page is about a different car, the 2003 Pontiac Grand Prix, 2003 Chevrolet Malibu, and 2003 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.
- Manufacturer does not provide testing procedures for many individual systems and components. A malfunction in Intake Air Temperature (IAT) sensor circuit can set a DTC. For testing procedures and specifications, perform related DTC testing procedure. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article. An out-of-calibration IAT sensor may not set a DTC. Use the following procedure to test sensor calibration.
- Disconnect IAT sensor harness connector. See Fig 1. Using DVOM, measure resistance between terminals of IAT sensor at specified temperatures. See TEMPERATURE VS. RESISTANCE table. Resistance should be high when air temperature is cold and drop as air temperature warms. With vehicle sitting overnight, ECT sensor and IAT sensor should have close to the same resistance reading. If resistance is not within specification, replace IAT sensor.
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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.