OBD-II Code P0418 – Secondary Air Injection Relay A Malfunction

The P0418 code indicates that the ECM has detected a malfunction in the Secondary Air Injection (SAI) Relay A circuit. This relay manages the air pump that helps reduce cold-start emissions. When the relay fails or wiring becomes faulty, it can lead to higher emissions and a Check Engine Light.

🔍 What Does Code P0418 Mean?

Code P0418 is triggered when the ECM detects abnormal voltage or no signal from the Air Injection Relay A circuit. The secondary air injection system helps reduce emissions by injecting fresh air into the exhaust manifold. A relay or wiring fault interrupts this process, causing higher emissions during startup.

⚠️ Common Symptoms

• Check Engine Light illuminated
• Smog test failure due to high emissions
• Air pump not activating during cold start
• Rough idle when starting engine
• Possible burning smell from relay area

🔧 Common Causes of P0418

• Faulty Secondary Air Injection Relay A
• Broken or shorted wiring in the SAI circuit
• Corrosion on relay connectors
• Blown fuse in the air injection system
• Faulty ECM signal output (rare)

🧰 Diagnosis Steps Using iCarsoft CR Max BT

1. Connect the iCarsoft CR Max BT scanner to the OBD-II port.
2. Turn ignition ON (engine off).
3. Read stored DTCs and confirm code P0418.
4. Inspect SAI relay and wiring for damage or corrosion.
5. Use a multimeter to check power and ground continuity.
6. Perform an actuator test via iCarsoft CR Max BT to trigger the relay.
7. Replace or repair faulty components, then clear codes.

🧩 Repair Solutions for P0418

• Replace the faulty SAI relay A
• Repair open or shorted wiring in the circuit
• Clean corroded connectors with electrical contact cleaner
• Verify air pump operation after relay replacement
• Clear the code and test drive

✅ Prevention Tips

• Keep underhood electrical components clean and dry.
• Apply dielectric grease to relay terminals to prevent corrosion.
• Use iCarsoft CR Max BT for regular diagnostics to detect early issues.

The iCarsoft CR Max BT provides advanced diagnostic functions and actuator control, allowing accurate detection and quick repair of faults like P0418.