GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2002 🢒 Corvette 🢒 Engine 🢒 Engine Controls - 5.7L 🢒 DTC P0418

Circuit Description

A voltage is directly supplied to the relay coil of the secondary air injection (AIR) pump. The powertrain control module (PCM) controls the relay by grounding the control circuit via an internal switch that is 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 PCM receives a different voltage, from the fault detection circuit , than expected, 2 events occur. The fault line status changes, and the DTC sets.

The relay controls the high current flow to the AIR fuel-injection pump. This allows the PCM driver to control only the relatively low current that is used by the relay.

Conditions for Running the DTC
    • The engine speed is more than 400 RPM.
    • The system 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.
    • All the above conditions exist 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.
    • Clear the MIL and the DTC with a scan tool.

Diagnostic Aids

AIR Pump Relay Terminal Identification

Front of Vehicle

Left Side of Vehicle

Ignition

B+

Right Side of Vehicle

Pump Supply

Control

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. Listen for a click when the relay operates. Command the ON state and the OFF state. Repeat the commands as necessary.

    2.

  2. This step tests for voltage at the coil side of the relay.

    3.

  3. This step verifies that the PCM is providing ground to the AIR pump relay.

    4.

  4. This step tests if a ground is constantly being applied to the AIR pump relay.

    5.

  5. If the control circuit and the connection at the PCM are OK, the PCM may be faulty.

    6.

  6. This DTC will not report a pass. The scan tool status for this DTC will not report a pass. The scan tool will only display if the diagnostic test fails. The repair is not complete if the scan tool indicates that the diagnostic test ran and failed.

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

  1. Connect a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Command the AIR pump relay ON and OFF with a scan tool.

Does the relay turn ON and OFF with each command?

Go to Step 3

Go to Step 4

3
  1. Review the Freeze Frame/Failure Records for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle under the conditions which set the DTC, use the following information:
    5. • The data in the Freeze Frame/Failure Records
    • The parameters listed in the Conditions for Running in the DTC

Does this DTC set?

Go to Step 4

Go to Intermittent Conditions

4

  1. Turn OFF the ignition.
  2. Remove the AIR pump relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Test the ignition 1 voltage circuit at the relay for an open with a test lamp connected to a good ground.

Does the test lamp illuminate?

Go to Step 5

Go to Step 11

5

  1. Connect a test lamp between the following 2 circuits of the AIR pump relay:
    2. • The AIR pump relay control circuit
    • The ignition 1 voltage circuit
  2. Command the relay ON and OFF with a scan tool. Refer to Diagnostic Aids for terminal identification.

Does the test lamp turn ON and OFF with each command?

Go to Step 9

Go to Step 6

6

Does the test lamp remain illuminated with each command?

Go to Step 8

Go to Step 7

7

  1. Test the AIR pump relay control circuit for a short to voltage, or for an open. Refer to Circuit Testing in Wiring Systems.
  2. If you find a condition, repair the condition as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 14

Go to Step 10

8
  1. Test the AIR pump relay control circuit for a short to ground. Refer to Circuit Testing in Wiring Systems.
  2. If you find a condition, repair the condition as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 14

Go to Step 13

9
  1. Inspect for poor connections at the AIR pump relay. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
  2. Repair conditions as necessary. Refer to Repairing Connector Terminals in Wiring Systems.

Did you find and correct the condition?

Go to Step 14

Go to Step 12

10
  1. Inspect for poor connections at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
  2. If you find a condition, repair the condition as necessary. Refer to Repairing Connector Terminals in Wiring Systems.

Did you find and correct the condition?

Go to Step 14

Go to Step 13

11

Repair the ignition 1 voltage circuit of the AIR pump relay. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 14

--

12

Replace the AIR pump relay.

Did you complete the replacement?

Go to Step 14

--

13

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

Go to Step 14

--

14

  1. Use a scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

Go to Step 15

Go to Step 2

15

With a scan tool, observe the stored information Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

Go to Diagnostic Trouble Code (DTC) List

System OK