Automotive Service Excellence (ASE) A8 Engine PerformanceEmissions Control Systems Diagnosis and RepairMedium
A vehicle with an Air Injection Reaction (AIR) system is diagnosed with a 'Check Engine' light and a DTC P0410, 'Secondary Air Injection System Malfunction'. The technician observes that the AIR pump runs continuously after engine start-up, even when the engine is warm. What is the MOST likely cause of this continuous operation?
- AA stuck open AIR pump diverter valve.
- BA restricted air injection passage.
- CA faulty AIR pump check valve.
- DA shorted AIR pump relay.
Show answer & explanationAnswer & explanation
Correct answer: D. A shorted AIR pump relay.
A continuous running AIR pump, especially when it shouldn't be (e.g., when the engine is warm), is a strong indicator of an electrical issue. A shorted AIR pump relay would keep the pump energized regardless of the ECU's command, leading to continuous operation and a P0410 code.
Why the other options are wrong
- A. A stuck open diverter valve would direct air to the wrong place or allow exhaust into the system, but wouldn't cause the pump itself to run continuously if the relay is off.
- B. A restricted air injection passage would prevent air from reaching the exhaust, leading to inefficient operation and P0410, but not continuous pump running.
- C. A faulty check valve would allow exhaust gas into the pump, potentially damaging it or causing noise, but not continuous operation.
Shorted AIR Pump Relay
An electrical malfunction in the AIR pump relay where the contacts are permanently closed, causing the secondary air injection pump to run continuously, regardless of engine conditions or ECU commands.
- Causes continuous AIR pump operation.
- Often results in DTC P0410 (Secondary Air Injection System Malfunction).
- Leads to excessive noise and potential pump wear.
Memory trick: Relay's Runaway: The pump won't stop, the relay's got a short.