Quick answer: The P0418 code indicates an electrical malfunction in the Secondary Air Injection System control circuit. It directly affects the emissions equipment responsible for reducing cold-start tailpipe pollution. This issue has medium urgency, meaning your engine will run fine, but you will likely fail a state emissions test.
Noticing a Check Engine Light pop up on your dashboard is never fun, especially when you plug in an OBD-II scanner and find a specific code staring back at you. If that code happens to be P0418, you are dealing with an issue in your car’s smog reduction system. This guide will walk you through what the code means, why it happens, and how to fix it without wasting money.
What Does P0418 Mean?
The Powertrain Control Module (PCM) sets diagnostic trouble code P0418 when it detects an electrical fault in the Secondary Air Injection (SAI) system control circuit. When you start your car cold, the SAI pump forces fresh air directly into the exhaust stream. This extra oxygen helps burn up unburned fuel left over from a rich cold-start mixture, which quickly heats up the catalytic converter. The P0418 code specifically points to a fault in the electrical circuit-such as a bad relay, a blown fuse, broken wiring, or a failed pump motor-rather than a mechanical vacuum leak.
Symptoms
- Illuminated Check Engine Light on the dashboard.
- Failure to pass an annual emissions or smog test.
- An unusual whining or electric motor sound coming from under the hood during a cold start, or no sound at all from the pump.
- No noticeable difference in how the engine drives or idles.
Possible Causes
Before you start replacing expensive components, remember that the most common mistake is swapping out the SAI pump itself when the actual culprit is a simple, cheap relay or fuse.
- Blown fuse or a failed secondary air injection relay.
- Corroded, frayed, or loose wiring and electrical connectors at the air pump or relay.
- Failed Secondary Air Injection pump motor.
- Faulty Powertrain Control Module (rare, but possible if internal drivers fail).
Check These Yourself Before Visiting a Mechanic
- Locate your vehicle’s fuse box, find the fuse and relay associated with the secondary air injection pump, and check them for continuity or obvious burn marks.
- Inspect the wiring harness running to the air pump located near the front bumper or inner fender to ensure no rodent damage or loose connectors exist.
How to Fix It
- Replace any blown fuses and swap out the air pump relay with a known good matching relay from the fuse box.
- Use a digital multimeter to check for voltage at the air pump electrical connector while commanding the pump on during a cold start or via a bidirectional OBD-II scan tool.
- Test the SAI pump motor directly by applying 12 volts from the battery to see if it spins.
- Repair or replace damaged wiring harnesses, or replace the air pump assembly if the motor itself is internally shorted or seized.
Estimated Repair Costs (2026)
| Job | Parts ($) | Labor ($) |
|---|---|---|
| Fuse or Relay Replacement | $10 – $30 | $0 – $50 |
| Wiring Repair | $15 – $50 | $75 – $150 |
| Secondary Air Injection Pump Replacement | $150 – $450 | $100 – $200 |
Note: these are 2026 estimates in US dollars; costs vary by make and model.
Frequently Asked Questions
Can I drive with the P0418 code?
Yes, you can drive your car safely. The secondary air injection system only operates for a couple of minutes during a cold start to lower emissions. It does not affect engine performance, fuel economy, or drivability, though you should fix it before your vehicle inspection due date.
How do I clear the P0418 code?
You can clear the code using any standard OBD-II code reader plugged into the diagnostic port under your dashboard. However, if the underlying electrical fault-such as a bad relay or broken wire-is not repaired, the Check Engine Light and code P0418 will return almost immediately.
Will this code clear itself if I fix the problem?
Yes, if you repair the faulty component, the Check Engine Light will usually turn off on its own after several normal driving cycles. Alternatively, you can use an OBD-II scanner to manually clear the code and reset the system readiness monitors instantly.