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:
^ 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 ignition voltage is between 9-18 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 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: 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 condition is intermittent, refer to Intermittent Conditions. Intermittent Conditions

TEST DESCRIPTION

Steps 1-10:

Steps 11-17:

The numbers below refer to the step numbers on the diagnostic table.
1. The Diagnostic System Check-Computers and Controls Systems prompts you to complete some basic checks and store the Freeze Frame/Failure Records on the scan tool.
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 feed.
4. This step verifies that the control module is providing a ground.
5. This step tests if ground is constantly being applied.
12. The control module utilizes electrically erasable programmable read only memory (EEPROM). When the control module is replaced, the new control module must be programmed.