P0418

Schematic:

CIRCUIT DESCRIPTION

Ignition voltage is supplied directly to the secondary Air Injection (AIR) pump relay. The Powertrain Control Module (PCM) controls the relay by grounding the control circuit via an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. Each driver has a fault line which is monitored by the PCM. When the PCM is commanding a component on, the voltage of the control circuit should be near 0 volts. When the PCM is commanding the control circuit to a component off, the voltage potential of the circuit should be near battery voltage. If the fault detection circuit senses a voltage other than what is expected, this DTC will set.

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

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

CONDITIONS FOR RUNNING THE DTC
^ The ignition voltage is between 9.0-18.0 volts.
^ The engine speed is more than 80 RPM.
^ The PCM driver transitions from ON to OFF or from OFF to ON.

CONDITIONS FOR SETTING THE DTC
^ A short to ground, an open circuit, or a short to battery voltage is detected on the control circuit.
^ The condition is present for at least 30 seconds.

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

CONDITIONS FOR CLEARING THE MIL/DTC
^ The PCM turns the Malfunction Indicator Lamp (MIL) off after 3 consecutive drive trips that the diagnostic runs and does not fail.
^ A current DTC clears when the diagnostic runs and does not fail.
^ A History DTC clears after 40 consecutive warm-up cycles if this or any other emission related diagnostic does not report any failures.
^ Use a scan tool in order to clear the MIL/DTC.
^ Interrupting the PCM battery voltage may or may not clear DTCs. This practice is not recommended.

DIAGNOSTIC AIDS

NOTE:
^ Refer to Test Probe Notice in Service Precautions.
^ Do not operate the AIR pump for more than 60 seconds. Continuous operation of the AIR pump in excess of 60 seconds will damage the AIR pump.

If the problem is intermittent, refer to Intermittent Conditions.


TEST DESCRIPTION

Steps 1 - 8:

Steps 9 - 13:

The numbers below refer to the step numbers on the diagnostic table.
1. The Powertrain On Board Diagnostic (OBD) System Check prompts you to complete some basic checks and store the Freeze Frame and Failure Records data on the scan tool.
2. Listen for an audible click when the relay operates. Command both the ON and OFF states. Repeat the commands as necessary.
3. Tests for voltage at the coil feed side of the relay.
4. Verifies that the PCM is providing ground to the relay.
5. Determines if ground is constantly being applied to the relay.
12. The PCM utilizes an electrically Erasable Programmable Read-only Memory (EEPROM). When the PCM is replaced, the new PCM must be programmed.