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.