Automotive Service Excellence (ASE) A8 Engine PerformanceEmissions Control Systems Diagnosis and RepairHard
A vehicle with an Air Injection Reaction (AIR) system is diagnosed with a 'Check Engine' light and DTC P0410 (Secondary Air Injection System Malfunction). Inspection reveals that the AIR pump is running continuously, even when the engine is warm and at normal cruising speed. What is the MOST likely cause?
- AA shorted AIR pump relay circuit keeping the pump energized.
- BA faulty exhaust oxygen sensor providing incorrect readings.
- CA restricted vacuum line to the AIR system check valve.
- DA stuck-open AIR system diverter valve.
Show answer & explanationAnswer & explanation
Correct answer: A. A shorted AIR pump relay circuit keeping the pump energized.
If the AIR pump is running continuously, it means it's receiving constant power. This is typically caused by a short in the relay circuit that keeps the relay closed, thus energizing the pump even when the PCM is not commanding it on.
Why the other options are wrong
- B. A faulty oxygen sensor could affect air-fuel ratio and catalytic converter efficiency, but it would not directly cause the AIR pump to run continuously.
- C. A restricted vacuum line to the check valve would affect air delivery to the exhaust, but not cause the pump itself to run continuously.
- D. A stuck-open diverter valve would direct air to the exhaust continuously, but the pump would only run when commanded by the PCM, not continuously.
AIR Pump Continuous Operation
Continuous operation of the AIR pump, especially when not commanded, typically indicates an electrical fault, most commonly a shorted relay circuit.
- Leads to premature pump failure.
- Can cause rich exhaust conditions.
- Often accompanied by DTCs like P0410.
Memory trick: Pump won't stop? Relay's stuck, circuit's short, it's a power lock!