Electronic Control System Signature, ISX and QSX15 Engines – FAULT CODE 256

Ambient Air Temperature Sensor Circuit


Overview

CODE REASON EFFECT
Fault Code: 256
PID: P171
SPN: 171
FMI: 4/4
LAMP: Yellow
SRT: 

Low voltage detected at the ambient air temperature circuit.

No effect on engine 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 (automotive only).

Ambient Air Temperature Sensor Circuit
SMALL | MEDIUM | LARGE

Circuit Description

The ambient air temperature sensor is used by the electronic control module (ECM) to monitor the temperature of the ambient air. The ambient air temperature signal is used by the ECM for the idle shutdown ambient air temperature override and ICON™ features.

Component Location

The ambient air temperature sensor location is OEM dependent. Use the OEM troubleshooting and repair manual.

Shop Talk

The resistance of the sensor varies with the temperature. The reading you observe should compare to this table:

Temperature (°C)
Temperature [°F]
Resistance (ohms)
0
32
30k to 36k
25
77
9k to 11k
50
122
3k to 4k
75
167
1350 to 1500
100
212
600 to 675

Refer to Troubleshooting Fault Code t05-256.

Last Modified:  26-Oct-2010