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 Relay Control Circuit: Description
Ignition voltage is supplied directly to relay. Powertrain Control Module (PCM) supplies ground path to relay control circuit via an internal solid state device called a driver. Each driver has a fault line which is monitored by PCM. When PCM commands relay on, voltage on control circuit should be low, about zero volts. When PCM commands relay off, voltage on control circuit should be high, about battery voltage. DTC sets when fault detection circuit senses a voltage other than what is expected. PCM will monitor control circuit for a short to ground, short to voltage, open circuit, open relay, internally shorted or excessively low resistance relay.
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.