Automotive Service Excellence (ASE) A8 Engine PerformanceEmissions Control Systems Diagnosis and RepairHard
A technician is diagnosing a vehicle that intermittently runs rough, especially during acceleration, and sometimes has a 'Check Engine' light with no specific DTCs. The vehicle uses a hot-wire Mass Air Flow (MAF) sensor. During a live data stream, the technician observes that the MAF sensor reading occasionally drops to 0.0 g/s for a brief moment before returning to normal, even though the engine is running. What is the most probable cause of this intermittent issue?
- AA vacuum leak in the intake manifold
- BAn intermittent open circuit in the MAF sensor wiring or connector
- CA contaminated MAF sensor sensing element
- DA failing fuel pump
Show answer & explanationAnswer & explanation
Correct answer: B. An intermittent open circuit in the MAF sensor wiring or connector
A MAF sensor reading intermittently dropping to 0.0 g/s while the engine is running strongly suggests an electrical issue, specifically an intermittent open circuit in the wiring or connector. If the sensing element were simply contaminated, it would likely provide an inaccurate but continuous reading, not drop to zero. A vacuum leak or failing fuel pump would cause performance issues but wouldn't typically make the MAF sensor read 0.0 g/s.
Why the other options are wrong
- A. A vacuum leak would cause a lean condition and potentially high fuel trims, but the MAF sensor would still report airflow, not drop to 0.0 g/s.
- C. A contaminated MAF sensor would typically cause inaccurate readings (e.g., lower than actual airflow), leading to a lean condition, but would not cause the reading to drop to zero.
- D. A failing fuel pump would cause fuel starvation symptoms (stalling, hesitation) but would not directly cause the MAF sensor to read 0.0 g/s.
MAF Sensor Intermittent Zero Reading
A Mass Air Flow sensor that intermittently reports 0.0 g/s (or similar minimum) while the engine is running, indicating a loss of signal.
- Strongly suggests an intermittent open circuit in wiring or connector.
- Can cause rough running, stalling, and various driveability issues.
- Requires careful inspection of wiring harness and connector pins.
Memory trick: MAF goes zero? Connection's loose, signal's a hero!