DTC P0418 L26, NU3

The secondary air injection (AIR) system aids in the reduction of hydrocarbon emissions during a cold start. The system forces fresh filtered air into the exhaust stream in order to accelerate the catalyst operation. An electric air pump, the secondary AIR injection pump, provides filtered air on demand to the AIR control solenoid valve/pressure sensor assembly. The AIR control solenoid valve/pressure sensor assembly controls the flow of air from the AIR pump to the exhaust manifold. The AIR valve relay supplies the current needed to operate the AIR control solenoid valve/pressure sensor assembly. A pressure sensor is used to monitor the air flow from the AIR pump. The powertrain control module (PCM) supplies the internal pressure sensor with a 5-volt reference, an electrical ground, and a signal circuit.

The AIR diagnostic uses 3 phases to test the AIR system:

1. DTCs P0411 and P2430 run during Phase 1
2. DTCs P2430 and P2440 run during Phase 2
3. DTC P2444 runs during Phase 3

During phase 1, both the AIR pump and the solenoid valve are activated. Normal secondary air function occurs. Expected system pressure is 8-10 kPa above BARO.

During phase 2, only the AIR pump is activated. The solenoid valve is closed. Pressure sensor performance and solenoid valve deactivation are tested. Expected system pressure is 15-20 kPa above BARO.

During phase 3, neither the AIR pump nor the solenoid valve is activated. AIR pump deactivation is tested. Expected system pressure equals BARO.

In all 3 phases, testing is accomplished by comparing the measured pressure against the expected pressure. The PCM can detect faults in the AIR pump, AIR control solenoid valve/pressure sensor assembly, and the exhaust check valve. The pressure sensor can also detect leaks and restrictions in the secondary AIR system plumbing.

DTC P0418 is a type B DTC.

DTC P0418 is a type B DTC.

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Electrical Information Reference

DTC Type Reference

Scan Tool Reference

Ignition ON, enable and disable the affected relay with a scan tool. Feel or listen to verify that the affected relay turns ON and OFF with each command.

1. Ignition OFF, disconnect the affected relay.
2. Ignition ON, connect a test lamp between the positive terminal at the battery and the relay control circuit terminal.
3. Command the relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp is always ON, test the relay control circuit for a short to ground. If the circuit tests normal, replace the PCM.

⇒	If the test lamp is always OFF, test the relay control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the PCM.

4. Connect an appropriately fused jumper wire between the positive voltage terminal at the battery and the load voltage supply circuit terminal and verify load activation.

⇒	If the load does not activate, test the load voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the load.

5. Ignition ON, connect an appropriately fused jumper wire between the relay switch voltage supply circuit terminal and the load voltage supply circuit terminal and verify load activation.

⇒	If the load does not activate, test the relay switch voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal and its fuse is open, test all components connected to the fuse and replace as necessary.

6. Ignition ON, verify that a test lamp illuminates between the relay coil voltage supply circuit terminal and ground.

⇒	If the test lamp does not illuminate, test the affected relay coil voltage supply circuit for a short to ground or an open/high resistance.

7. If all circuits and the PCM test normal, test or replace the affected relay.

Relay Test

1. Test between the normally-closed switch terminals, if any, for 0 ohms.
2. Test between the normally-open switch terminals for infinite ohms.
3. Test between each switch terminal and either coil terminal for infinite ohms.
4. Connect the relay coil terminals to ground and fused power to energize the relay.
5. Test between each switch terminal and each coil terminal for 0 volts.
6. Test between the normally-closed switch terminals, if any, for infinite ohms.
7. Test between the normally-open switch terminals for 0 ohms.

Control Module References for control module replacement and programming

Ignition ON, command the affected relay ON and OFF with a scan tool. Feel or listen to verify that the relay turns ON and OFF with each command.