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Ambient Air Temperature Sensor Circuit
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Overview
| CODE | REASON | EFFECT |
| Fault Code: 256 PID: P171 SPN: 171 FMI: 4/4 LAMP: Amber SRT: |
Ambient Air Temperature Sensor Circuit – Shorted Low. Low voltage detected at ambient air temperature circuit. |
None on performance. The idle shutdown ambient air temperature override feature will use the intake manifold air temperature sensor value to determine idle shutdown and availability of override. |
 Ambient Air Temperature Sensor Circuit
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Circuit Description
The ambient air temperature sensor is used by the ECM to monitor ambient air temperature. This could be used to sense the temperature inside the cab of a vehicle or the air temperature outside the vehicle. The ambient air temperature signal is used by the ECM for the idle shutdown ambient air temperature override feature.
Component Location
The mounting location for the ambient air temperature sensor is OEM dependent. Refer to the appropriate OEM troubleshooting and repair manual.
Shop Talk
Possible causes of this fault code include:
- Signal circuit shorted to ground in the harness.
- Signal circuit shorted to return or ground in the sensor.
| Temperature (°F) | Temperature (°C) | Resistance (ohms) |
| 25 | -4 | 39k to 44k |
| 44 | 7 | 22k to 25k |
| 64 | 18 | 13k to 15k |
| 84 | 29 | 8k to 9k |
| 104 | 40 | 5k to 6k |
Refer to Troubleshooting Fault Code t05-256
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