P0101

What it means

P0101 is the generic code for a Mass or Volume Air Flow Sensor 'A' circuit range or performance fault. The engine control unit has compared the airflow reading with what it expects from throttle position, engine speed, load and other sensors, and found the figures do not agree. The sensor signal is still present, but it appears implausible or out of step with the rest of the engine data.

Symptoms

• Engine management light on
• Hesitation or poor acceleration
• Rough idle or hunting idle
• Occasional stalling or difficult starting
• Black smoke or a noticeably rich or lean running condition
• Poor fuel economy

Possible causes

• Dirty or contaminated air flow sensor element, or sensor drifting out of rangelikely
• Unmetered air entering after the sensor: split intake hose, loose clamp, cracked breather or crankcase ventilation hose, or leaking intake manifold gasketlikely
• Restricted air intake, such as a badly clogged air filter or a collapsed or blocked intake ductpossible
• Wiring or connector fault at the air flow sensor: corrosion, chafing, high resistance or poor earth or supplypossible
• Exhaust leak ahead of the oxygen sensors or a fault in another related sensor (throttle position, manifold pressure, barometric pressure) causing a plausibility mismatchpossible
• Faulty air flow sensor internallypossible
• Outdated or faulty control unit software, where a manufacturer bulletin identifies it as a cause for the specific modelrare

How to diagnose

1. Read the stored and pending codes and the freeze frame data, noting engine speed, load and temperature when the fault set, and check for other related codes such as fuel trim, throttle or manifold pressure faults
2. Visually inspect the air filter, intake duct, air filter box and all hoses between the sensor and the engine for splits, loose clamps, disconnected breather pipes and oil contamination
3. Inspect the sensor connector and wiring for damage, corrosion, bent pins and water ingress, and check for chafing along the loom
4. Check the live air flow reading at idle and under load against the expected value for the engine, and compare it with throttle position and manifold pressure readings
5. Review short and long term fuel trims at idle and at a steady 2500 rpm to help separate a leak after the sensor from a faulty sensor
6. Check for intake leaks with a suitable smoke test, and inspect the exhaust for leaks upstream of the oxygen sensors
7. Test the sensor's power supply, earth and signal circuit against the manufacturer's specification for that model, as the sensor type and test values vary
8. Check for any applicable software update or technical bulletin for the vehicle once the mechanical and electrical checks are complete

How to fix

• Clean the air flow sensor element only with a cleaner approved for the purpose and following the manufacturer's guidance, or replace the sensor if it is damaged or still out of range
• Repair or replace split, loose or disconnected intake hoses, breather hoses and manifold gaskets to remove any unmetered air
• Replace a clogged air filter and clear any blockage in the intake ducting
• Repair or replace damaged wiring, connectors or terminals in the sensor circuit
• Repair any exhaust leak and replace any other faulty sensor identified during testing
• Update the control unit software only if the manufacturer identifies an outdated calibration as a cause for that vehicle

Can I keep driving?

This code for other makes

• P0101AudiLarge vacuum leaks, Split Intake Air Boot or PCV Hose, Defective intake manifold gaskets, Mass Airflow Sensor (MAF), Mass Air Flow Sensor circuit and or wiring problems, Defective Barometric Pressure Sensor, Dirty or contaminated Mass Air Flow Sensing wire or filament, PCM software needs to be updated

Nearby codes

• P0100GenericMass or Volume Air Flow Sensor A Circuit
• P0102GenericMass or Volume Air Flow Sensor A Circuit Low