For 1990-2009 cars

The secondary air injection (AIR) system is used to accelerate the heating process of the catalytic converters by introducing outside air into the exhaust manifold. The AIR system operates on cold engine starts when the catalytic converters work least efficient. The powertrain control module (PCM) controls the air pump motor by controlling the ground for the air pump relay coil. The PCM monitors the relay coil circuit for low and high voltage faults. DTC P0418 sets when the air pump relay is commanded OFF and the feedback voltage at the PCM is low.

### DTC Parameters

DTC P0418 will set if air pump relay feedback voltage is less than 1.25 volts with air pump relay commanded OFF when:

• | The condition exists for longer than 0.5 seconds.

• | The ignition is ON.

DTC P0418 diagnostic runs continuously with ignition ON and air pump relay commanded OFF.

DTC P0418 is a type D DTC.

### Diagnostic Aids

To locate an intermittent problem, use a scan tool to monitor the AIR PUMP REL. - LOW VOLT or AIR PUMP REL. - OPEN test with ignition ON, engine OFF. When a fault , open or short to ground exists, the scan tool will display TEST FAIL for both tests.

The tests will fail only when the device is being commanded OFF and the voltage at the PCM is low. The tests update every 100 ms whenever the ignition is turned ON and the device is being commanded OFF via the scan tool or PCM.

The AIR pump relay coil resistance is 75-105 ohms.