CODE 79, TRANSMISSION FLUID OVERTEMP
PCM supplies and monitors a 5-volt reference to sensor. As transmission temperature changes, sensor resistance changes, affecting monitored voltage. When fluid is cold, resistance is high, resulting in a high monitored voltage. When fluid is hot, resistance is low, resulting in a low monitored voltage. Code will set if transmission temperature is 120-130°C for 5 seconds and Codes 58 and 59 are not set.
Note. Test numbers refer to numbers on diagnostic chart.
- Checks for out-of-calibration sensor or shorted circuit. 2 Simulates Code 59.
Check harness for potential short to ground. See Code 59 chart to check transmission temperature sensor temperature-to-resistance values. Also, check transmission fluid level. Check for conditions which could cause transmission to overheat i.e. trailer towing, steep grades, etc.
| Temperature °F (°C) | Ohms |
|---|---|
| 212 (100) | 177 |
| 194 (90) | 241 |
| 158 (70) | 467 |
| 104 (40) | 1459 |
| 68 (20) | 3520 |
| 23 (-5) | 12,300 |
| 14 (-10) | 16,180 |
| 0 (-18) | 25,000 |
| 4 (-20) | 28,680 |
| 22 (-30) | 52,700 |
| 40 (-40) | 100,700 |
TEMPERATURE-TO-RESISTANCE VALUES (Measure resistance across sensor terminals)
