Subaru Legacy BN/BS (2015-2019) Service Manual: Dtc p0071 ambient air temperature sensor circuit "a" range/performance

Subaru Legacy BN/BS (2015-2019) Service Manual / Engine (diagnostics)(h4do) / Diagnostic procedure with diagnostic trouble code (dtc) / Dtc p0071 ambient air temperature sensor circuit "a" range/performance

DTC DETECTING CONDITION:

Detected when two consecutive driving cycles with fault occur.

CAUTION:

After servicing or replacing faulty parts, perform Clear Memory Mode Clear Memory Mode > OPERATION, and Inspection Mode Inspection Mode > PROCEDURE.

STEP	CHECK	YES	NO
1.CHECK FOR ANY OTHER DTC ON DISPLAY.	Is any other DTC displayed-	Check the appropriate DTC using the “List of Diagnostic Trouble Code (DTC)”. List of Diagnostic Trouble Code (DTC)	Diagnostic Procedure with Diagnostic Trouble Code (DTC) > DTC P0071 AMBIENT AIR TEMPERATURE SENSOR CIRCUIT "A" RANGE/PERFORMANCE
2.CHECK CURRENT DATA. 1) Turn the ignition switch to ON. 2) Read the value of «Ambient Air Temperature» using the Subaru Select Monitor or a general scan tool. NOTE: • Subaru Select Monitor For detailed operation procedures, refer to “Current Data Display For HVAC System”. Read Current Data • General scan tool For detailed operation procedures, refer to the general scan tool operation manual. 3) Read the change of the value in «Ambient Air Temperature» while heating and cooling the ambient sensor using a hair dryer. CAUTION: Do not heat the part to the temperature where you cannot touch it with your bare hand in order to prevent burning yourself and protect the part.	Does the value of «Ambient Air Temperature» change between heating and cooling-	Repair the poor contact of ECM connector.	Replace the ambient sensor. Ambient Sensor

1. OUTLINE OF DIAGNOSIS

Detect the malfunction of ambient temperature sensor characteristics.

After the engine starts after the specified period of soaking time has elapsed, judge by correlation between ambient temperature sensor value, intake air temperature sensor value and engine coolant temperature sensor value. Judge as NG when the differences are both above the specified value by comparing between ambient air temperature and intake air temperature, ambient air temperature and engine coolant temperature.

2. COMPONENT DESCRIPTION

Ambient temperature sensor is connected to combination meter. ECM receives the data of ambient temperature sensor via CAN communication with combination meter.

(1)

Ambient sensor

(2)

Resistance value (k-)

(3)

Ambient air temperature (°C (°F))

3. EXECUTION CONDITION

Secondary Parameters	Execution condition
Soaking time	≥ 21600 s
Block heater judgment	Completed
Block heater operation	Not in operation

4. GENERAL DRIVING CYCLE

Perform the diagnosis only once after the engine starts after a certain period of soaking time.

5. DIAGNOSTIC METHOD

If the duration of time while the following conditions are met is longer than the time indicated, judge as NG.

Judgment Value

Malfunction Criteria	Threshold Value
\|Ambient air temperature 30 sec. after engine start − Intake air temperature 30 sec. after engine start\|	> Value from Map
\|Ambient air temperature at engine start − Engine coolant temperature at engine start\|	> 25 °C (45°F)

Map

Ambient temperature

°C (°F)

−30

(−22)

(86)

(113)

(140)

|Ambient air temperature 30 sec. after engine start − Intake air temperature 30 sec. after engine start|

°C (°F)

(36°F)

(57.6°F)

Time Needed for Diagnosis: Less than 1 second

Malfunction Indicator Light Illumination: Illuminates when malfunction occurs in 2 continuous driving cycles.

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Other materials:

Caution
• Prior to starting work, pay special attention to the following:1. Always wear work clothes, a work cap, and protective shoes. Additionally, wear a helmet, protective goggles, etc. if necessary.2. Protect the vehicle using a seat cover, fender cover, etc.3. Prepare the service tools, clean cl ...