GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2004 🢒 Corvette 🢒 DTC 🢒 DTC P0418

Circuit Description

The secondary air injection (AIR) pump relay controls the high current flow to the AIR pump. Ignition voltage is supplied to the AIR pump relay coil when the ignition is ON. Battery positive voltage is supplied to the armature contacts at all times. The powertrain control module (PCM) controls the relay by supplying a ground path to the relay coil control circuit by an internal integrated circuit called an output driver module (ODM). The low side driver also incorporates a fault detection circuit that is continuously monitored by the PCM. The voltage on the control circuit should be battery voltage when the ignition is ON and the AIR pump relay is at rest. If the fault detection circuit measures a low voltage under this condition it is an indication of an open or short to ground on the control or ignition 1 circuits. An open AIR pump relay coil fault may also be present. If the PCM detects low voltage on the AIR pump relay control circuit when the AIR pump relay is commanded OFF or a high voltage when the AIR pump relay is commanded ON, DTC P0418 sets.

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

    2.

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

    3.

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

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

Inspect the ENG IGN 1 fuse.

Is the ENG IGN 1 fuse open?

Go to Step 13

Go to Step 3

3
  1. Turn ON the ignition, with the engine OFF.
  2. Command the secondary air injection (AIR) pump relay ON and OFF with a scan tool.
  3. Listen for a click when the relay operates. Repeat the commands as necessary.

Does the AIR pump relay turn ON and OFF with each command?

Go to Step 4

Go to Step 5

4
  1. Observe the Freeze Frame/Failure Records data for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/ Failure Records.

Does the DTC fail this ignition?

Go to Step 5

Go to Intermittent Conditions

5

  1. Turn OFF the ignition.
  2. Remove the AIR pump relay. Refer to Relay Replacement in Wiring Systems.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the ignition 1 voltage circuit at the AIR pump relay connector with a test lamp that is connected to a good ground. Refer to Probing Electrical Connectors in Wiring Systems.

Does the test lamp illuminate?

Go to Step 6

Go to Step 12

6

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

Does the test lamp turn ON and OFF when commanded with a scan tool?

Go to Step 10

Go to Step 7

7

Did the test lamp remain illuminated when the scan tool was commanded ON and OFF?

Go to Step 9

Go to Step 8

8

Important: The AIR pump may be damaged if the control circuit is shorted to voltage.

Test the AIR pump relay control circuit for a short to voltage or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 14

Go to Step 11

9

Important: The AIR pump may be damage if the control circuit is shorted to ground.

Test the AIR pump relay control circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 14

Go to Step 17

10

Test for an intermittent and for a poor connection at the AIR pump relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 18

Go to Step 16

11

Test for an intermittent and for a poor connection at the powertrain control module (PCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 18

Go to Step 17

12

Repair the open circuit in 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 18

--

13

Important: The ignition 1 voltage circuit of the AIR pump relay is spiced to other components of the vehicle.

Test all circuits and components that are supplied by the ENG IGN 1 fuse for excessive current draw. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 18

--

14
  1. Ensure all components are installed and all connections are secured.
  2. Command the AIR pump relay ON and OFF with a scan tool.

Does the AIR pump turn ON and OFF when commanded with a scan tool?

Go to Step 18

Go to Step 15

15
  1. Replace the AIR pump. Refer to Secondary Air Injection Pump Replacement .
  2. Replace the AIR pump fuse as necessary.

Did you complete the replacement?

Go to Step 18

--

16

Replace the AIR pump relay.

Did you complete the replacement?

Go to Step 18

--

17

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

Go to Step 18

--

18
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/ Failure Records.
  5. 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.

Does the DTC fail this ignition?

Go to Step 2

Go to Step 19

19

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

Go to Diagnostic Trouble Code (DTC) List

System OK