DTC P0418: Secondary Air Injection Pump Relay Control Circuit: Description

Ignition voltage is supplied directly to the relay. The control module supplies the ground path to the relay control circuit via an internal solid state device called a driver. Each driver has a fault line which is monitored by the control module. When the control module commands the relay ON, the voltage on the control circuit should be low, near 0 volts. When the control module commands the relay OFF, the voltage on the control circuit should be high, near battery voltage. If the fault detection circuit senses a voltage other than what is expected, this Diagnostic Trouble Code (DTC) will set. The control module will monitor the control circuit for the following items:

• A short to ground.
• A short to voltage.
• An open circuit.
• An open relay.
• An internally shorted or excessively low resistance relay.