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P0418



DTC P0418

DTC DESCRIPTOR

DTC P0418
Secondary Air Injection (AIR) Pump Control Circuit

DIAGNOSTIC FAULT INFORMATION
Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Testing and Inspection






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. 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 control module 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:
- 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) 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.

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.

With the ignition ON and the engine OFF, 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
1. With the ignition ON, the engine OFF, and the AIR pump relay enabled with a scan tool, observe the AIR pump relay and the AIR pump while manipulating all related wiring and connectors.
- If manipulation does affect the relay or the pump, repair the wire harness or connections.
2. With the ignition ON, the engine OFF, and the pump relay removed, connect a test lamp from the relay coil voltage supply circuit to ground and verify that the test lamp illuminates.
- If the test lamp does not illuminate, test the voltage supply circuit for an open, high resistance, or a short to ground.
3. With the ignition ON, the engine OFF, and the pump relay removed, connect a test lamp from the relay coil voltage supply circuit to the relay control circuit and verify that the test lamp does not illuminate.
- If the test lamp illuminates, test the control circuit for a short to ground. If the circuit test normal, replace the control module.
4. With the ignition ON, the engine OFF, and the pump relay removed, a test lamp connected from the relay coil voltage supply circuit to the relay control circuit, and the AIR pump relay enabled with a scan tool, verify that the test lamp illuminates.
- If the test lamp does not illuminate, test the relay control circuit for an open, high resistance, or a short to voltage. If the circuit test normal, replace the control module.
5. If all circuits and the control module test normal, replace the pump relay.

COMPONENT TESTING
Connect the relay coil connections to fused battery voltage and ground. Measure the resistance through the relay contacts at 0 ohms.
- If the resistance measures more than 0 ohms then replace the relay.

REPAIR INSTRUCTIONS
Control Module References for engine control module (ECM) replacement, setup, and programming.

REPAIR VERIFICATION
With the ignition ON and the engine OFF, enable and disable the AIR pump relay with a scan tool while observing that the pump relay and AIR pump operate.
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