A013

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION

The In-Car Temperature (ICT) sensor is a thermistor that controls the signal voltage to the Air Conditioning Programmer (ACP). The ACP applies a voltage on CKT 734 to the sensor. When the sensor is cold the resistance is high and the ACP senses high signal voltage. As the sensor warms, the resistance becomes less and the signal voltage is pulled low through the sensor ground, CKT 407. Signal voltage varies between 5V (open circuit) and 0V (short circuit).


TEST CONDITION(S)

1. Ignition "ON."

2. Outside air temperature reads above -20°F.

FAILURE CONDITION(S)

Signal voltage less than -34°C (open circuit) or greater than 99°C (short circuit).

if AD99="8640", DTC may set intermittently if sensor temperature falls below -20°F. DTC becomes history after sensor temperature increases.

ACTION TAKEN

1. ACP uses a substitute In-Car temperature, this allows for continued operation of the HVAC system.

2. ACP data parameter AD25 displays the actual In-Car temperature sensor reading.

NOTES ON FAULT TREE

Before performing diagnostic, display AD25. If value is not reasonably close to the actual air temperature at the sensor. Check for proper air flow across the sensor or proper terminal contact at sensor and ACP.

1. Display AD25, normal operating range is from -34°C to 99°C.

2. Low value indicates an open circuit. Jumper determines whether the wiring or sensor is the cause of the open.

3. High value indicates a short circuit. Removing the sensor determines whether the wiring or sensor is the cause of the short.

4. Open is in the wiring. Jumper determines if the open is in the ground wiring or the sensing wire.

5. Determines if the open is in the sense circuit or at the ACP connection/ACP internal.

6. Display AD25, AD26, AD27, and AD28. If all display approximately -40, repair open CKT 407 between ACP and C201 terminal "D." If AD25 and AD26 display approximately -40, repair open CKT 407 between C201 terminal "D" and splice S241. If only AD25 displays approximately -40, repair open CKT 407 between splice S241 and ICT sensor.

NOTES ON INTERMITTENT CONNECTION
If an intermittent DTC is being set, select ACP Snapshot Data for DTC and note value of ACP data parameter. Manipulate the related wiring while observing ACP data parameter. If a failure is induced, the displayed data parameter value will be outside the sensors normal operating range.