What Causes the Secondary Air Injection Malfunction in Mercedes-Benz?

[SanGrant]

Secondary air injection malfunction. The user needs to replace the air injection driver and the air pump to resolve the issue. This occurs because the power terminals of the air pump are energized, and the internal breakdown of the air injection driver causes the motor power line to remain continuously connected to the 50A fuse, leading to motor burnout due to prolonged operation. Car maintenance precautions: 1. When the engine is hot, never open the radiator cap: otherwise, you may be scalded by splashing coolant or high-temperature steam. After the engine cools down, check that the coolant level is between the full and low marks. If not, add distilled water, purified water, or antifreeze, ensuring the level does not exceed the full mark. If the coolant level drops rapidly in a short time, check the cooling system for leaks or visit a service station for inspection. 2. If the brake fluid level is between the high and low marks, it is normal. If it is near or below the lower limit, there may be a leak or excessive wear of the brake pads, and you should promptly visit a service station for inspection. 3. Check the tire pressure monthly at normal temperature: if it is below the standard, replenish the tire pressure promptly. The pressure should not be too high or too low, as it affects driving safety. 4. A normal spark plug has intact insulation ceramic: no cracks or leakage, and a spark plug gap of 0.8±0.0mm produces a strong blue spark during discharge. If abnormalities are found, adjust the gap or replace the spark plug.

[SanKaden]

I've seen many Mercedes-Benz owners encounter secondary air pump failures. A common issue is the aging and failure of that small electric motor, especially in vehicles with over 100,000 kilometers. The air pump blades seizing or the motor bearings grinding dry can both cause the pump to stop working. Additionally, the combination valve connected to the exhaust pipe is also prone to problems—if the valve flap gets stuck by carbon deposits, it won't close tightly, and in severe cases, exhaust gas can even backflow into the pump. Remember to check the vacuum lines for leaks; a finger-thick rubber tube aging and cracking can lead to insufficient vacuum. Last time I helped someone troubleshoot an S350, I found the three-way connector was broken—replacing the tube solved the problem.

[KeeganFitz]

From a mechanical principle perspective, the secondary injection system primarily operates via vacuum drive. During cold starts, the vehicle's ECU activates the air pump while simultaneously controlling the solenoid valve to utilize vacuum for opening the combination valve. Therefore, faults typically occur in three areas: pump failure preventing air delivery, solenoid valve malfunction failing to transmit vacuum signals, or valve carbon buildup causing jamming and preventing opening. Once, I detected normal air pump rotation but still encountered a fault code. Ultimately, it was traced to the control unit receiving erroneous data from the oxygen sensor, misjudging system abnormality. The issue was resolved after reprogramming.

[McCarson]

This issue is more likely to occur with frequent short-distance driving. The system only operates for a few dozen seconds when the engine is cold. If you often drive only 3-5 kilometers before shutting off the engine, moisture inside the combination valve may not be fully expelled, leading to rust and jamming. Clogged air pump filters are another contributing factor, especially during seasons with abundant willow catkins in northern regions. Last month, a C200 we serviced had its intake completely blocked by poplar catkins—the fault code automatically cleared after cleaning. We recommend occasionally driving at highway speeds to allow the high exhaust temperatures to dry out the valve internals.

[IsaacLee]

The electronic control section warrants thorough inspection. A short circuit in the vacuum solenoid valve coil (the small black cube mounted on the engine compartment side) can completely disable the entire system. When reading data streams with a diagnostic tool, pay close attention to the operating current value of the air pump, which should normally range between 15-20 amps. Excessively high current may indicate mechanical binding, while zero current generally confirms wiring issues. Additionally, check the 25A fuse in the engine compartment fuse box - if blown, the pump won't operate.

[AveryDella]

Experience tells me this type of failure has a chain reaction. A leaking combination valve can cause high-temperature exhaust gas to flow backward, which may burn the plastic impeller inside the air pump at best, or melt the connected intake pipe at worst. You can make a preliminary judgment by listening to the sound: during a normal cold start, there should be a noticeable hissing intake sound; if it's completely silent, the air pump likely isn't starting; if accompanied by metal grinding noises, it's usually a bearing failure. I recommend addressing it early—last year, a GLK ignored this issue and ended up damaging the oxygen sensor as well.