P0418

CIRCUIT 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. If the fault detection circuit senses a voltage other than what the PCM expects, the fault line status changes causing the Diagnostic Trouble Code (DTC) to set.

The relay controls the high current flow to the Secondary Air Injection (AIR) pump and the AIR solenoid. This allows the PCM driver to only have to control the relatively low current used by the relay.

CONDITIONS FOR RUNNING THE DTC
^ The engine speed is more than 400 RPM.
^ The ignition 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 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.
^ Use a scan tool in order to clear the MIL and the DTC.

DIAGNOSTIC AIDS
^ If you cannot duplicate the DTC, use the Freeze Frame/Failure Records in order to locate an intermittent condition in the following ways:
- Use the information included in the Freeze Frame/Failure Records in order to determine how many miles since the DTC set.
- Use the Fail Counter and Pass Counter in order to determine how many ignition cycles the diagnostic reported as a pass or a fail.
- Operate the vehicle within the same Freeze Frame conditions that you observed in order to isolate when the DTC failed. Use the following conditions for your tests:
^ The RPM
^ The load
^ The vehicle speed
^ The temperature
^ For an intermittent condition, refer to Intermittent Conditions. Intermittent Conditions

TEST DESCRIPTION

Steps 1-7:

Steps 8-15:

The numbers below refer to the step numbers on the diagnostic table.
2. Listen for a click when the relay operates. Command both the ON and OFF states. Repeat the commands as necessary.
3. This test can detect a partially shorted coil which would cause an excessive current flow. Leaving the circuit energized for 2 minutes allows the coil to warm up. When warm the coil may open, and the current drops to 0, or the coil may short, and the current goes above 0.75 amp.
4. The AIR pump relay is located on the AIR pump assembly.
5. Identify and test the relay coil terminals in order to avoid improper diagnosis.
13. If no trouble is found in the control circuit or the connection at the PCM, the PCM may be faulty. However, this is an extremely unlikely failure.
14. The repair is not complete if the scan tool indicates that the diagnostic ran and failed.