Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
DTC P0418: Secondary Air Injection Pump Relay Control Circuit: Description
The Powertrain Control Module (PCM) commands the Secondary Air Injection (AIR) pump relay on by supplying a ground to the control circuit of the AIR pump relay. The AIR pump relay supplies high current to the AIR pump supply voltage circuit. Voltage is supplied to the AIR pump relay though the ignition 1 voltage circuit, protected by a fuse. When the PCM commands the AIR pump relay on, the voltage on the control circuit should be low or near zero volts. When the PCM commands the AIR pump relay off, the voltage potential of the circuit should be high, near battery voltage. The PCM monitors the voltage and supplies the ground to the relay by means of an internal driver. If the PCM detects a voltage other than what is expected, DTC P0418 sets.
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.