Engine Temperature Sensor Inputs
Analog inputs such as Intake Air Temperature (P0112, P0113), Cylinder Head Temperature (P1289. P1290), Mass Air Flow (P0102, P0103) and Throttle Position (P0122, P0123) are checked for opens, shorts, or rationality by monitoring the analog -to-digital (A/D) input voltage.
The ECT rationality test checks to make sure that ECT is not stuck high in a range that causes other OBD to be disabled. If after a long (6 hour) soak, ECT is very high (> 230 °F) and is also much higher than IAT at start, it is assumed that ECT is stuck high. If after a long (6 hour) soak, ECT is stuck midrange between 175 °F (typical thermostat monitor threshold temperature) and 230 °F and is also much higher than IAT at start, it is assumed that ECT is stuck mid-range.
ECT SENSOR RATIONALITY CHECK OPERATION
| DTCs |
P0116 (ECT stuck high or midrange) |
| Monitor Execution |
Once per driving cycle |
| Monitor Sequence |
None |
| Sensors OK |
ECT, CHT, IAT |
| Monitoring Duration |
100 seconds to register a malfunction |
TYPICAL ECT SENSOR RATIONALITY CHECK ENTRY CONDITIONS
| Entry Condition |
Minimum |
Maximum |
| Engine-off time (soak time) |
360 min |
|
| Difference between ECT and IAT |
|
50 deg |
| Engine Coolant Temperature |
230 °F |
|
| Engine Coolant Temperature for stuck midrange condition |
160 °F |
230 °F |
TYPICAL ECT SENSOR RATIONALITY CHECK MALFUNCTION THRESHOLDS
| Catalyst, Misfire, Fuel System or HO2S Monitors have not run this drive cycle |
The CHT sensor measures cylinder head metal temperature as opposed to engine coolant temperature. At lower temperatures, CHT temperature is equivalent to ECT temperature. At higher temperatures, ECT reaches a maximum temperature (dictated by coolant composition and pressure) whereas CHT continues to indicate cylinder head metal temperature. If there is a loss of coolant or air in the cooling system, the CHT sensor will still provides an accurate measure of cylinder head metal temperature. If a vehicle uses a CHT sensor, the PCM software calculates both CHT and ECT values for use by the PCM control and OBD systems.
CYLINDER HEAD TEMPERATURE SENSOR CHECK OPERATION
| DTCs |
P1289 (high input), P1290 (low input), P1299 (fail-safe cooling activated) |
| Monitor Execution |
Continuous |
| Monitor Sequence |
None |
| Sensors OK |
Not Applicable |
| Monitoring Duration |
5 seconds to register a malfunction |
TYPICAL CHT SENSOR CHECK MALFUNCTION THRESHOLDS
Voltage < 0.41 volts or voltage > 4.95 volts
For P1299, MIL illuminates immediately if CHT > 270 o. Fuel shut-off is activated to reduce engine and coolant temperature |
INTAKE AIR TEMPERATURE SENSOR CHECK OPERATION
| DTCs |
P0112 (low input), P0113 (high input) |
| Monitor Execution |
Continuous |
| Monitor Sequence |
None |
| Sensors OK |
Not Applicable |
| Monitoring Duration |
5 seconds to register a malfunction |
TYPICAL IAT SENSOR CHECK MALFUNCTION THRESHOLDS
| Voltage < 0.20 volts or voltage > 4.93 volts |
| ECT, IAT, EOT Temperature Sensor Transfer Function |
| Volts |
A/D counts in PCM |
Temperature, degrees F |
| 4.89 |
1001 |
-40 |
| 4.86 |
994 |
-31 |
| 4.81 |
983 |
-22 |
| 4.74 |
970 |
-13 |
| 4.66 |
954 |
-4 |
| 4.56 |
934 |
5 |
| 4.45 |
910 |
14 |
| 4.30 |
880 |
23 |
| 4.14 |
846 |
32 |
| 3.95 |
807 |
41 |
| 3.73 |
764 |
50 |
| 3.50 |
717 |
59 |
| 3.26 |
666 |
68 |
| 3.00 |
614 |
77 |
| 2.74 |
561 |
86 |
| 2.48 |
508 |
95 |
| 2.23 |
456 |
104 |
| 1.99 |
407 |
113 |
| 1.77 |
361 |
122 |
| 1.56 |
3.19 |
131 |
| 1.37 |
280 |
140 |
| 1.20 |
246 |
149 |
| 1.05 |
215 |
158 |
| 0.92 |
188 |
167 |
| 0.80 |
165 |
176 |
| 0.70 |
144 |
185 |
| 0.61 |
126 |
194 |
| 0.54 |
110 |
203 |
| 0.47 |
96 |
213 |
| 0.41 |
85 |
221 |
| 0.36 |
74 |
230 |
| 0.32 |
65 |
239 |
| 0.28 |
57 |
248 |
| 0.25 |
51 |
257 |
| 0.22 |
45 |
266 |
| 0.19 |
40 |
275 |
| 0.17 |
35 |
284 |
| 0.15 |
31 |
293 |
| 0.14 |
28 |
302 |