For 1990-2009 cars

### Circuit Description

The purpose of the secondary air injection (AIR) system is to reduce the hydrocarbon (HC), the carbon monoxide (CO), and the oxides of nitrogen (NOx) exhaust emissions by causing any combustible gases in the exhaust to reburn. This also causes the catalytic converters and the heated oxygen sensors (HO2S) to reach the normal operating temperatures more quickly, thus the Closed Loop operation occurs earlier.

When the engine is started, the engine control module (ECM) commands the AIR pump relay and the AIR cut-off valve vacuum control solenoid ON, injecting clean air into the engine exhaust ports. The ECM switches the AIR system OFF when the oxygen sensors become active. The AIR cut-off valve prevents air from being drawn into the system when the AIR pump is OFF. The vacuum to the valve is controlled by the AIR cut-off valve vacuum control solenoid. A check valve close to the engine prevents hot exhaust gases from backing up into the AIR system.

The secondary air injection pump relay receives switched battery power from the engine controls power relay. The ECM 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 that is monitored by the ECM. When the ECM commands a component ON, the voltage of the control circuit should be low, near 0 volts. When the ECM commands a component OFF, the voltage potential of the control circuit should be high, near battery voltage. If the fault detection circuit senses a voltage other than what is expected, this diagnostic trouble code (DTC) will set.

### Conditions for Running the DTC

• | The engine speed is more than 40 RPM.

• | The battery voltage is between 7.5-15 volts.

• | The above conditions are present for 300 ms (0.3 seconds).

### Conditions for Setting the DTC

A short to ground, an open circuit, or a short to battery voltage is detected on the control circuit.

### 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

• | Inspect other circuits that are spliced into the switch B+ circuit for their proper operation.

• | This DTC will only diagnose the air pump relay control circuit from the switched B+ to the ECM.

Use the J 35616 Connector Test Adapter Kit for any test that requires probing the ECM harness connector or a component harness connector.

Check for the following conditions:

• | Poor connections at the ECM or at the component--Inspect the harness connectors for any backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

• | Damaged harness--Inspect the wiring harness for any damage. If the harness appears to be OK, observe the scan tool while moving the related connectors and the wiring harnesses. A change in the display may help in order to locate the fault.

Refer to Intermittent Conditions for the intermittents.

### Test Description

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

1. Listen for an audible click when the relay operates. Repeat the commands as necessary.

2. This check can detect a partially shorted coil which would cause an excessive current flow. Leaving the circuit energized for 2 minutes allows the coil to warm up. When warm, the coil may open, the amps drop to 0, or short, go to above 0.20 amp.

3. Perform the Idle Learn Procedure when replacing the ECM or the throttle body.

#### DTC P0418 Secondary Air Injection (AIR) Pump Relay Control Circuit

Step | Action | Values | 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. Turn ON the ignition, with the engine OFF.
2. Using the scan tool, command the relay ON and OFF.
3. Listen or touch the relay while commanding the relay ON and OFF.

Does the relay turn ON and OFF?

--

Go to Step 3

Go to Step 5

3 |

1. Turn OFF the ignition.
2. Disconnect the ECM.
3. Jumper the engine controls power relay control circuit to ground in order to supply power to the secondary air injection pump relay coil.
4. Set the DMM on 10-amp scale in order to measure current flow.
5. Connect the DMM between the secondary air injection pump relay control circuit in the ECM harness connector and ground for 2 minutes.

Is the amperage within the specified range?

100-200 mA

Go to Diagnostic Aids

Go to Step 4

4 |

1. Turn OFF the ignition.
2. Disconnect the secondary air injection pump relay.
3. Use the DMM in order to measure the resistance from the secondary air injection pump relay control circuit in the ECM harness connector to ground. The DMM should display an infinite resistance.

Does the DMM display an infinite resistance?

--

Go to Step 13

Go to Step 11

5 |

1. Turn OFF the ignition.
2. Disconnect the secondary air injection pump relay.
3. Using an unpowered test lamp connected to ground, probe the switched B+ circuit in the secondary air injection pump relay harness connector.
4. Turn ON the ignition. The test lamp should illuminate.

Does the test lamp illuminate?

--

Go to Step 6

Go to Step 12

6 | Using an unpowered test lamp connected to ground, probe the secondary air injection pump relay control circuit in the secondary air injection pump relay harness connector. The test lamp should NOT illuminate. Is the test lamp OFF? | -- | Go to Step 7 | Go to Step 10
7 | Using an unpowered test lamp connected to B+, probe the secondary air injection pump relay control circuit in the secondary air injection pump relay harness connector. The test lamp should NOT illuminate. Is the test lamp OFF? | -- | Go to Step 8 | Go to Step 11
8 |

1. Turn OFF the ignition.
2. Disconnect the ECM.
3. Install the secondary air injection pump relay.
4. Jumper the engine controls power relay control circuit to ground in order to supply power to the secondary air injection pump relay coil.
5. Set the DMM on 10-amp scale in order to measure current flow.
6. Connect the DMM between the secondary air injection pump relay control circuit in the ECM harness connector and ground for 2 minutes.

Is the amperage within the specified range?

100-200 mA

Go to Step 15

Go to Step 9

9 |

1. Test the secondary air injection pump relay control circuit for an open or high resistance.
2. Repair the wiring as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 17

Go to Step 13

10 |

1. Inspect the secondary air injection pump relay control circuit for a short to B+.
2. Repair the wiring as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 17

Go to Step 15

11 |

1. Inspect the secondary air injection pump relay control circuit for a short to ground.
2. Repair the wiring as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 17

Go to Step 15

12 | Repair the switched B+ circuit to the secondary air injection pump relay. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 17 | --
13 |

1. Test for a poor connection or poor terminal tension at the relay connector. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
2. Repair as necessary. Refer to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 17

Go to Step 14

14 | Replace the secondary air injection pump relay. Did you complete the replacement? | -- | Go to Step 17 | --
15 |

1. Test for poor a connection or poor terminal tension at the ECM harness connector. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
2. Repair as necessary. Refer to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 17

Go to Step 16

16 | Important:

• | Perform the idle learn procedure when replacing the ECM or the throttle body.

• | This vehicle is equipped with a theft deterrent system which interfaces with the engine control module (ECM). Program the new ECM with the frequency code of the theft deterrent module that is currently on the vehicle.

Replace the ECM. Refer to Engine Control Module Replacement .

Did you complete the action?

--

Go to Step 17

--

17 |

1. Use the 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 18

Go to Step 2

18 | 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