P0104 – Mass Air Flow (MAF) Sensor Circuit Intermittent

The Diagnostic Trouble Code (DTC) P0104 indicates that the Engine Control Module (ECM/PCM) has detected an intermittent or erratic signal from the Mass Air Flow (MAF) sensor. Instead of providing a stable airflow measurement, the sensor signal changes unexpectedly or is temporarily lost, causing incorrect fuel calculations and poor engine performance.

Symptoms

• Check Engine Light is illuminated.
• Intermittent rough idle.
• Engine hesitation during acceleration.
• Occasional loss of power.
• Poor fuel economy.
• Engine may stall unexpectedly.
• Intermittent hard starting.

Possible Causes

• Loose or damaged MAF sensor connector.
• Intermittent open or short circuit in the wiring.
• Corroded electrical terminals.
• Dirty or failing MAF sensor.
• Poor ground connection.
• Damaged intake duct allowing unmetered air.
• ECM fault (rare).

Diagnostic Procedure

1. Read all stored and pending DTCs.
2. Inspect the MAF connector for loose pins or corrosion.
3. Check the wiring harness while gently moving it (wiggle test).
4. Inspect the intake hose for cracks or loose clamps.
5. Clean the MAF sensor using an approved MAF cleaner.
6. Verify power supply, ground, and signal circuits.
7. Replace the sensor only after confirming an intermittent internal failure.

Live Data Diagnosis (Autel Scanner)

Using an Autel scan tool:

1. Go to ECM → Live Data.
2. Monitor the MAF (g/s) parameter.
3. At idle, airflow is typically between 2–7 g/s, depending on engine size.
4. Observe the reading while gently moving the wiring harness.
5. If the airflow value suddenly drops to zero, spikes unexpectedly, or fluctuates without engine speed changes, inspect the connector, wiring, and sensor.

Typical MAF Signal Path

Air Filter
     │
     ▼
MAF Sensor
     │
Signal
     ▼
ECM / PCM
     │
Fuel Injection Calculation

Note: Connector pin assignments, wiring colors, voltage values, and signal characteristics vary by vehicle manufacturer and model. Always consult the appropriate wiring diagram for the vehicle being diagnosed.

Smoke Test

If a smoke machine is available, inspect the intake system for leaks.

• Check the intake boot.
• Inspect vacuum hoses.
• Inspect the intake manifold.
• Repair any leaks found after the MAF sensor.

Although P0104 is primarily an intermittent electrical fault, intake leaks should still be ruled out during diagnosis.

Common Repairs

• Clean the MAF sensor.
• Repair or replace damaged wiring.
• Repair loose or corroded terminals.
• Replace the MAF connector if necessary.
• Repair intake air leaks.
• Replace the MAF sensor if testing confirms failure.

Important Note

P0104 often results from intermittent wiring or connector problems rather than a defective MAF sensor. Perform a thorough visual inspection, wiggle test, and live data analysis before replacing any components.