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 279 (ENGINE CONTROLS - SYSTEM & COMPONENT TESTING)SENSORS & SWITCHESENGINE COOLANT TEMPERATURE SENSOR
1999 GMC Forward Control 5.7 R, Automatic
Engine Coolant Temperature Sensor
1999 GMC Forward Control 5.7 R, AutomaticSECTION Engine Coolant Temperature Sensor
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.
- A malfunction in Engine Coolant Temperature (ECT) sensor circuit can set a DTC. For testing procedures and specifications, perform appropriate diagnostic test. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 4.6L DEVILLE & SEVILLE article. An out-of-calibration ECT sensor may not set a DTC. Use the following procedure to test sensor calibration.
- Disconnect ECT sensor harness connector. See COMPONENT LOCATIONS . Using DVOM, measure resistance of ECT sensor at specified temperatures. See SENSOR TEMPERATURE VS. RESISTANCE table. Resistance should be high when engine is cold and drop as engine warms. With vehicle sitting overnight, IAT sensor and ECT sensor should have close to the same resistance reading. If resistance is not within specification, replace ECT sensor.
SENSOR TEMPERATURE VS. RESISTANCE
| Temperature - °F (°C) | (1) Ohms | ||
|---|---|---|---|
| 302 (150) | 47 | ||
| 284 (140) | 60 | ||
| 266 (130) | 77 | ||
| 248 (120) | 100 | ||
| 230 (110) | 132 | ||
| 212 (100) | 177 | ||
| 194 (90) | 241 | ||
| 176 (80) | 332 | ||
| 158 (70) | 467 | ||
| 140 (60) | 667 | ||
| 122 (50) | 973 | ||
| 113 (45) | 1188 | ||
| 104 (40) | 1459 | ||
| 95 (35) | 1802 | ||
| 86 (30) | 2238 | ||
| 77 (25) | 2796 | ||
| 68 (20) | 3520 | ||
| 59 (15) | 4450 | ||
| 50 (10) | 5670 | ||
| 41 (5) | 7280 | ||
| 32 (0) | 9420 | ||
| 23 (-5) | 12,300 | ||
| 14 (-10) | 16,180 | ||
| 5 (-15) | 21,450 | ||
| -4 (-20) | 28,680 | ||
| -22 (-30) | 52,700 | ||
| -40 (-40) | 100,700 | ||
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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.