P0418

CIRCUIT DESCRIPTION
Ignition voltage is supplied directly to the relay. The control module supplies the ground path to the relay control circuit via an internal solid state device called a driver. Each driver has a fault line which is monitored by the control module. When the control module commands the relay ON, the voltage on the control circuit should be low, near 0 volts. When the control module commands the relay OFF, the voltage on the control circuit should be high, near battery voltage. If the fault detection circuit senses a voltage other than what is expected, this diagnostic trouble code (DTC) will set.

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

CONDITIONS FOR RUNNING THE DTC
^ The engine is running for more than 30 seconds.
^ The system voltage is between 9-18 volts.

CONDITIONS FOR SETTING THE DTC
^ The control module detects an improper voltage level on the control circuit.
^ The condition exists for more than 30 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

NOTE: Refer to Continuous Operation of the Air Pump Notice in Service Precautions.

IMPORTANT: Use the J 35616-A connector test adapter kit for any test that requires probing the following items:
^ The PCM harness connectors
^ The electrical center fuse/relay cavities
^ The component terminals
^ The component harness connector

Using this kit will prevent damage caused by the improper probing of connector terminals.

If the DTC cannot be duplicated and is determined to be intermittent, reviewing the Failure Records can be useful in determining when the DTC was last set. Also refer to Intermittent Conditions. Intermittent Conditions

TEST DESCRIPTION

Steps 1-2:

Steps 3-14:

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 step tests for voltage at the switch feed.
4. This step verifies that the control module is providing a ground.
5. This step tests if ground is constantly being applied.