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

WARNING: This page is about a different car, the 2003 Cadillac Seville and 2003 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.

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.