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P0418 is a diagnostic trouble code (DTC) for "Secondary Air Injection System Relay A circuit Malfunction". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.
A P0418 trouble code is an indicator that a problem has occurred in the secondary air injection system. Some codes related to P0718 include P0410, P0411, P0412, P0413, P0414, P0415, P0416, P0417, and P0419 trouble codes.
A P0418 trouble code is stored on the PCM when voltage readings from the secondary air injection system register a difference of more than 10 percent over manufacturer's specifications. In addition to storing the code and illuminating the Check Engine light on initial detection, some vehicle models require multiple ignition cycles before an indicator lamp is lit.
The causes of a P0418 trouble code often occur during cold weather and include water entering the secondary injection valve system via a faulty one-way check valve. Some other causes include wiring and connectors becoming burnt by high-temperature engine exhaust and an overloaded circuit, resulting in a blown fuse.
Symptoms of this code include engine hesitation when accelerating and stalling at startup and while idling. Another indication of a problem with the secondary air injection system is abnormal noise generating from the components.
Diagnosing a P0418 trouble code requires the mechanic to use a digital volt/ohmmeter and an advanced scanner. In addition to these tools, the mechanic also needs to perform the following steps when diagnosing:
Mechanics oftentimes fail to drain excess water from the pump housing when replacing a damaged secondary air injection pump. This, in turn, leads to the pump refreezing upon exposure to cold temperatures and the pump binding up and failing again. This problem is further increased if a mechanic fails to inspect and replace a faulty one-way check valve, which allows moisture to buildup and the pump to fail again upon water allowed into the system freezing.
If this problem is not fixed before cold weather hits, the water in the system can freeze and bind the pump, causing it to fail. Failure of the secondary air injection pump leads to higher emissions from the affected vehicle.
To fix a P0418 trouble code, the mechanic should perform the following repairs if the secondary air injection system wiring, connectors, or components are found to be faulty:
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