P0418

CIRCUIT DESCRIPTION
A voltage is directly supplied to the relay coil of the secondary air injection (AIR) pump. The powertrain control module (PCM) controls the relay by grounding the control circuit via an internal switch that is 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. If the PCM receives a different voltage, from the fault detection circuit, than expected, 2 events occur. The fault line status changes, and the DTC sets.

The relay controls the high current flow to the AIR fuel-injection pump. This allows the PCM driver to control only the relatively low current that is used by the relay.

CONDITIONS FOR RUNNING THE DTC
^ The engine speed is more than 400 RPM.
^ The system voltage is between 6-18 volts.

CONDITIONS FOR SETTING THE DTC
^ The PCM detects that the commanded state of the driver and the actual state of the control circuit do not match.
^ All the above conditions exist for a minimum of 5 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






TEST DESCRIPTION

Steps 1-9:

Steps 10-15:

The numbers below refer to the step numbers on the diagnostic table.
2. Listen for a click when the relay operates. Command the ON state and the OFF state. Repeat the commands as necessary.
4. This step tests for voltage at the coil side of the relay.
5. This step verifies that the PCM is providing ground to the AIR pump relay.
7. This step tests if a ground is constantly being applied to the AIR pump relay.
13. If the control circuit and the connection at the PCM are OK, the PCM may be faulty.
14. This DTC will not report a pass. The scan tool status for this DTC will not report a pass. The scan tool will only display if the diagnostic test fails. The repair is not complete if the scan tool indicates that the diagnostic test ran and failed.