GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2001 🢒 Firebird 🢒 Body and Accessories 🢒 Wiring Systems 🢒 DTC P0418

Circuit Description

The powertrain control module (PCM) controls the relay by grounding the control circuit via an internal driver switch. The primary function of the driver is to supply 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 fault detection circuit senses a voltage other than what the PCM is expects, the fault line status changes causing the DTC to set.

The relay controls the high current flow to the AIR injection pump. This allows the PCM driver to only have to control the relatively low current that the relay uses.

Conditions for Running the DTC
    • The engine speed is more than 400 RPM.
    • The ignition 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 are present 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

Important: 

   • Before you service the PCM, remove any debris from the PCM connector surfaces. Inspect the PCM connector gaskets when you diagnose or replace the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion into the PCM.
   • For any test that requires probing the PCM or probing a component harness connector, use the J 35616 connector test adapter kit. Using this kit prevents damage to the harness and component terminals. Refer to Using Connector Test Adapters in Wiring Systems.

    • The scan tool offers 3 modes of AIR output controls:
       - The AIR pump relay
       - The AIR solenoid
       - The AIR system
    • For underhood fuse block terminal identification, refer to Electrical Center Identification Views in Wiring Systems.
    • For an intermittent condition, refer to Intermittent Conditions .

Test Description

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

  1. Listen for a click when the relay operates. Ensure that both the ON and the OFF states are commanded. Repeat the commands as necessary.

    2.

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

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 AIR pump fuse

Is the AIR pump fuse open?

Go to Step 3

Go to Step 4

3
  1. Disconnect the AIR vacuum solenoid connector.
  2. Test the B+ supply using a test lamp connected to B+ for a short to ground.

Does the test illuminate?

Go to Step 13

Go to Step 4

4

  1. Install 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 AIR pump relay turn ON and OFF with each command?

Go to Step 5

Go to Step 6

5
  1. Review 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, as specified in the supporting text, or as close as possible to the Freeze Frame/Failure Records data that you observed.

Does the DTC reset?

Go to Step 6

Go to Intermittent Conditions

6

  1. Turn OFF the ignition.
  2. Disconnect the AIR pump relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the AIR pump relay B+ supply circuit with the test lamp connected to ground. Refer to Probing Electrical Connectors in Wiring Systems.

Does the test lamp illuminate?

Go to Step 7

Go to Step 13

7

  1. Connect a test lamp between the control circuit of the AIR pump relay and the B+ supply circuit of the AIR pump relay.
  2. Command the AIR pump relay ON and OFF with the scan tool.

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

Go to Step 11

Go to Step 8

8

Does the test lamp remain illuminated with each command?

Go to Step 10

Go to Step 9

9
  1. Test the control circuit of the AIR pump relay for the following conditions:
    2. • A short to voltage
    • 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 16

Go to Step 12

10
  1. Test the control circuit of the AIR pump relay 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 Circuit Testing in Wiring Systems.

Did you find and correct the condition?

Go to Step 16

Go to Step 12

11
  1. Inspect for poor connections at the AIR pump relay. Refer to Testing for Electrical Intermittents in Wiring Systems.
  2. If you find a condition, repair the condition as necessary. Refer to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 16

Go to Step 14

12
  1. Inspect for poor connections at the PCM. Refer to Testing for Electrical Intermittents in Wiring Systems.
  2. If you find a condition, repair the condition as necessary. Refer to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 16

Go to Step 15

13

Repair the B+ supply circuit between the AIR fuse and the AIR relay or solenoid. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 16

--

14

Replace the AIR pump relay.

Did you complete the replacement?

Go to Step 16

--

15

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

Go to Step 16

--

16
  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 as specified in the supporting text.

Does the DTC run and pass?

Go to Step 17

Go to Step 2

17

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