DTC Descriptor
DTC P0418 : Secondary Air Injection (AIR) Pump Control CircuitDiagnostic Fault Information
Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Pump Relay Coil Supply | P0102, P0412, P0418, | P0418 | P0690, P0418 | -- |
Pump Relay Control | P0418 | P0418 | P0411, P0418, P0690, P2431 | -- |
Pump Relay Switch Supply | P0411 | P0411 | -- | -- |
Circuit/System Description
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. The secondary AIR injection pump, provides filtered air on demand to the AIR check valve assembly. The AIR check valve assembly controls the flow of air from the AIR pump to the exhaust manifold. The AIR CNTRL relay supplies the current needed to operate the AIR solenoid that is integral to the check valve assembly. A pressure sensor, also integral to the check valve assembly, is used to monitor the air flow from the AIR pump. The control module supplies the internal pressure sensor with a 5-volt reference, an electrical ground, and a signal circuit. The signal circuit provides the control module with a voltage relative to internal AIR pressure changes.
The AIR diagnostic uses 3 phases to test the AIR system:
| • | DTCs P0411 and P2430 run during Phase 1 |
| • | DTCs P2430 and P2440 run during Phase 2 |
| • | DTC P2444 runs during Phase 3 |
In all 3 phases, testing is accomplished by comparing the measured pressure against the expected pressure. The control module 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.
Conditions for Running the DTC
| • | The system voltage is between 9-18 volts. |
| • | This DTC runs on a 250 ms loop. |
| • | This DTC runs continuously once the above conditions are met. |
Conditions for Setting the DTC
| • | The actual and expected states of the AIR Pump Relay Control Circuit do not match. |
| • | The condition exists for at least 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) at the beginning of the fourth ignition cycle, after 3 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 and related Freeze Frame data clears after 40 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. |
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation Reference
Secondary Air Injection System Description
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Circuit/System Verification
Important: If you cannot duplicate the condition, 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.
Ignition ON, command the AIR pump relay ON and OFF with a scan tool. Listen for the operation of the AIR pump relay and AIR pump.
Circuit/System Testing
- Ignition OFF, disconnect the AIR pump relay.
- Ignition ON, connect a test lamp between the positive terminal at the battery and the relay control circuit terminal.
- Command the AIR pump relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
- Connect a 50-amp fused jumper wire between the positive voltage terminal at the battery and the pump voltage supply circuit terminal and verify pump activation.
- Ignition ON, connect a 50-amp fused jumper wire between the relay switch voltage supply circuit terminal and the AIR pump voltage supply circuit terminal and verify pump activation.
- Ignition ON, verify that a test lamp illuminates between the relay coil voltage supply circuit terminal and ground.
- If all circuits and the control module test normal, test or replace the relay.
| ⇒ | If the test lamp is always ON, test the relay control circuit for a short to ground. If the circuit tests normal, replace the ECM. |
| ⇒ | 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 ECM. |
| ⇒ | If the pump does not activate, test the pump voltage supply circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the AIR pump. |
| ⇒ | If the pump 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 or replace the relay. |
| ⇒ | 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. If the circuit tests normal and its fuse is open, test or replace the relay. |
Component Testing
Relay Test
- Test between the normally closed switch terminals, if any, for 0 ohms.
- Test between the normally open switch terminals for infinite ohms.
- Test between each switch terminal and either coil terminal for infinite ohms.
- Connect the relay coil terminals to ground and fused power to energize the relay.
- Test between each switch terminal and each coil terminal for 0 volts.
- Test between the normally closed switch terminals, if any, for infinite ohms.
- Test between the normally open switch terminals for 0 ohms.
Repair Instructions
| • | Control Module References for engine control module (ECM) replacement, setup, and programming |
Repair Verification
Ignition ON and the engine OFF, enable and disable the AIR pump relay with a scan tool while listening for the AIR pump relay and AIR pump to operate.
