GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2002 🢒 Eldorado 🢒 DTC 🢒 DTC P0418

Circuit Description

The powertrain control module (PCM) commands the AIR pump relay ON by grounding the control circuit though an internal switch called a driver. Voltage is supplied to the AIR pump relay though the ignition 1 voltage circuit and battery positive voltage circuit that are fuse protected. When the PCM commands the relay ON, the voltage of the control circuit should be low or near 0 volts. When the PCM commands the AIR pump relay OFF, the voltage potential of the circuit should be high, near battery voltage. If the PCM detects a voltage other than what is expected, this DTC will set.

Conditions for Running the DTC
    • The engine is running.
    • The system voltage is between 8-16 volts.

Conditions for Setting the DTC
    • The PCM detects an improper voltage level on the output circuit that controls the AIR pump relay.
    • The condition exists for at least 10 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

An intermittent may be caused by any of the following conditions:

    • A poor connection
    • Rough through wire insulation
    • A broken wire inside the insulation
    • Spread terminal contacts
    • Corroded connections and wiring

The PCM will monitor the control circuit for the following:

    • A short to ground
    • A short to voltage
    • An open circuit
    • An internally shorted or excessively low resistance relay coil

When the PCM detects any of the above malfunctions, this DTC will set and the diagnostic will be disabled.

Thoroughly inspect any circuit that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring Systems.

Test Description

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

  1. Listen for a click when the relay operates. Be sure 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

Are DTCs P0102, P0410, P0412, and P0443 set?

Go to Step 3

Go to Step 4

3

Important: Replace the IGN 1 fuse after completing the repair.

Locate and repair the following circuit conditions:

    • Short to ground in the ignition 1 voltage circuit between the IGN 1 fuse and the AIR solenoid or AIR relay
    • Shorted component that shares the ignition feed fuse--Refer to Power Distribution Schematics in Wiring Systems.

Did you complete the repair?

Go to Step 17

--

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 Diagnostic Aids

6

  1. Turn OFF the ignition.
  2. Remove the AIR pump relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the AIR pump relay ignition supply circuit with the J 35616-200 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 ignition supply circuit of the AIR pump relay.
  2. Command the AIR pump relay ON and OFF with a 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 15

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 open in the ignition 1 voltage circuit for the AIR pump relay. 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

Observe the stored information in Capture Info. with a scan tool.

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

Go to Diagnostic Trouble Code (DTC) List

System OK