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

Ignition voltage is supplied directly to AIR injection pump relay coil. Powertrain Control Module (PCM) controls relay by grounding control circuit through an internal switch called a driver. Primary function of driver is to supply ground for component being controlled. Each driver has a fault line which is monitored by PCM.

When PCM is commanding a component ON, voltage of control circuit should be low (near zero volts). When PCM is commanding control circuit to a component off, voltage potential of circuit should be high (near battery voltage).