P0418

CIRCUIT DESCRIPTION
The powertrain control module (PCM) commands the AIR pump relay ON by grounding the control circuit though an internal switch called a driver. Voltage is supplied to the AIR pump relay though the ignition 1 voltage circuit and battery positive voltage circuit that are fuse protected. When the PCM commands the relay ON, the voltage of the control circuit should be low or near 0 volts. When the PCM commands the AIR pump relay OFF, the voltage potential of the circuit should be high, near battery voltage. If the PCM detects a voltage other than what is expected, this DTC will set.

CONDITIONS FOR RUNNING THE DTC
^ The engine is running.
^ The system voltage is between 8-16 volts.

CONDITIONS FOR SETTING THE DTC
^ The PCM detects an improper voltage level on the output circuit that controls the AIR pump relay.
^ The condition exists for at least 10 seconds.

ACTION TAKEN WHEN THE DTC SETS
^ The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
^ The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
^ A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
^ A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
^ Clear the MIL and the DTC with a scan tool.

DIAGNOSTIC AIDS
An intermittent may be caused by any of the following conditions:
^ A poor connection
^ Rough through wire insulation
^ A broken wire inside the insulation
^ Spread terminal contacts
^ Corroded connections and wiring.

The PCM will monitor the control circuit for the following:
^ A short to ground
^ A short to voltage
^ An open circuit
^ An internally shorted or excessively low resistance relay coil

When the PCM detects any of the above malfunctions, this DTC will set and the diagnostic will be disabled.

Thoroughly inspect any circuit that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent and Poor Connections in Diagnostic Aids.

If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Diagnostic Aids.

TEST DESCRIPTION

Steps 1-8:

Steps 9-17:

The numbers below refer to the step numbers on the diagnostic table.
4. Listen for a click when the relay operates. Ensure that both the ON and the OFF states are commanded. Repeat the commands as necessary.
6. This step tests for voltage at the coil side of the AIR pump relay.
7. This step verifies that the PCM is providing ground to the AIR pump relay.
8. This step tests if a ground is constantly being applied to the AIR pump relay.