P0418

Diagnostic Chart:

Schematic:

CIRCUIT DESCRIPTION
Ignition voltage is supplied directly to the 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 low, near 0 volts. When the PCM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be high, near battery voltage. If the fault detection circuit senses a voltage other than what is expected, DTC P0418 will set.

The PCM will monitor the control circuit for the following conditions:
^ 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 will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.
^ The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data.
^ If the misfire is determined to be catalyst damaging, the PCM will flash the MIL.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic has been run and passed.
^ The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
^ The DTC can be cleared by using a scan tool.

DIAGNOSTIC AIDS

NOTE: Use the connector test adapter kit J 3561 6-A 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.

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.

IMPORTANT: Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

^ Poor terminal connection-Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Use a corresponding mating terminal to test for proper tension.
^ Damaged harness-Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault.
^ PCM and engine grounds for clean and secure connections

If the DTC is determined to be intermittent, reviewing the Failure Records can be useful in determining when the DTC was last set.

TEST DESCRIPTION
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 tests and inspections 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. This step tests for voltage at the coil feed side of the relay.
4. This step verifies that the PCM is providing ground to the relay.
5. This step tests 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.