Possible causes

– Faulty Air Pump inoperative
– Air bypass solenoid harness is open or shorted
– Air bypass solenoid circuit poor electrical connection

When is the code detected?

If the fault detection circuit senses a voltage other than what the Powertrain Control Module (PCM) is expects, the fault line status changes causing the code P0418 to set.

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)
– Engine hesitation

P0418 BUICK Description

The Powertrain Control Module (PCM) controls the relay by grounding the control circuit via an internal switch called a driver. The primary function of the driver is to supply the ground for the controlled component. Each driver has a fault line which the PCM monitors. When the PCM commands a component ON, the voltage of the control circuit should be low (near 0 volts). When the PCM commands the control circuit to a component OFF, the voltage potential of the circuit should be high (near the battery voltage).
The relay controls the high current flow to the AIR injection pump integral bypass valve. This allows the PCM driver to only have to control the relatively low current used by the relay.