Subaru Legacy BN/BS (2015-2019) Service Manual: Dtc p0101 mass or volume air flow sensor "a" circuit range/performance

Subaru Legacy BN/BS (2015-2019) Service Manual / Engine (diagnostics)(h6do) / Diagnostic procedure with diagnostic trouble code (dtc) / Dtc p0101 mass or volume air flow sensor "a" circuit range/performance

DTC DETECTING CONDITION:

Detected when two consecutive driving cycles with fault occur.

TROUBLE SYMPTOM:

• Improper idling

• Engine stalls.

• Poor driving performance

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)	Replace the mass air flow and intake air temperature sensor. Mass Air Flow and Intake Air Temperature Sensor

1. OUTLINE OF DIAGNOSIS

Detect the malfunction of air flow sensor output properties.

Judge as a low side NG when the air flow voltage indicates a small value regardless of running in a state where the air flow voltage increases. Judge as a high side NG when the air flow voltage indicates a large value regardless of running in a state where the air flow voltage decreases. Judge air flow sensor property NG when the Low side or High side becomes NG.

2. COMPONENT DESCRIPTION

(A)	Air

(1)	Air flow sensor	(3)	Voltage (V)	(4)	Amount of intake air (kg (lb)/s)
(2)	Intake air temperature sensor

3. EXECUTION CONDITION

Secondary Parameters	Execution condition
Low
Engine coolant temperature	≥ 75 °C (167 °F)
Engine speed	≥ 1600 rpm
Throttle valve opening angle	≥ 15 °
Intake manifold pressure	≥ 73.3 kPa (550 mmHg, 21.7 inHg)
High
Engine coolant temperature	≥ 75 °C (167 °F)
Engine speed	525 rpm — 800 rpm
Throttle valve opening angle	< 5.2 °
Intake manifold pressure	≥ 47.3 kPa (355 mmHg, 14 inHg)

4. GENERAL DRIVING CYCLE

Perform the diagnosis continuously after idling.

5. DIAGNOSTIC METHOD

Judge as NG when Low side or High side becomes NG.

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
Low
Output voltage	< 1.41 V
High
Output voltage	≥ 1.82 V

Time Needed for Diagnosis:

Low: 5000 ms

High: 5000 ms

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

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