P0418
Secondary Air Injection System Control A Circuit
Encountering the engine check light code P0418 signifies an explicit mechanical or electrical operational breakdown categorized as "Secondary Air Injection System Control A Circuit". Professional scanner tools usually flag this subsystem loop early on.
Driver's Summary
Code P0418 means your vehicle detected a problem with the secondary air injection system control a circuit system. Typical symptoms include check engine light, failed emissions. You can continue normal driving, but schedule an inspection at your next service appointment to clear this code properly.
Symptoms
Check engine light, failed emissions
Common Causes
- Failed secondary air injection pump relay
- Defective air injection pump
- Open circuit in pump wiring
- Blown main pump fuse
How to Fix
- 1 Test and replace pump relay
- 2 Replace secondary air pump
- 3 Repair wiring harness
- 4 Replace maxi-fuse
Technical Explanation
Code P0418 is confirmed when the ECM's diagnostic algorithm detects a parameter deviation that persists across a defined number of consecutive drive cycles. EGR flow is verified by monitoring changes in MAP sensor readings before and after valve actuation; correct EGR flow produces a predictable pressure drop in the intake manifold that the ECM can measure with precision. The fault remains stored in memory even after the MIL is cleared; it becomes a confirmed DTC after failing two consecutive drive cycles, and the PCM logs a freeze frame record of the engine's exact operating state at the moment of detection.
Is It Safe to Drive?
Immediate safety risk is low with P0418 active. The primary concern is regulatory — this fault will cause a failed emissions test — and the secondary risk is that the small root cause (failed secondary air injection pump relay) becomes a larger problem if ignored for months.
Mechanic's Pro Tip
Before replacing any component on P0418, spend 5 minutes inspecting the wiring harness and connector first — corrosion, chafed insulation, and backed-out pins cause the majority of these faults and cost nothing to fix. Use a multimeter to measure voltage drop across the connector pins under load; anything above 0.1V indicates excessive resistance that will cause intermittent failures even after replacing the sensor.
Related Fault Codes
Frequently Asked Questions
What does OBD2 code P0418 mean?
OBD2 code P0418 refers to Secondary Air Injection System Control A Circuit. Encountering the engine check light code P0418 signifies an explicit mechanical or electrical operational breakdown categorized as "Secondary Air Injection System Control A Circuit". Professional scanner tools usually flag this subsystem loop early on.
What are the most common symptoms of DTC P0418?
Drivers experiencing code P0418 typically report: Check engine light, failed emissions.
Is it safe to drive with trouble code P0418 active?
Immediate safety risk is low with P0418 active. The primary concern is regulatory — this fault will cause a failed emissions test — and the secondary risk is that the small root cause (failed secondary air injection pump relay) becomes a larger problem if ignored for months.
How much does it cost to fix code P0418?
The estimated repair cost for P0418 ranges from $20 to $400 USD. Relay/Fuse: $20 - $50; Air pump: $150 - $400
Relay/Fuse: $20 - $50; Air pump: $150 - $400
Need Professional Diagnostic Assistance?
Always verify sensor signals and wiring integrity with an OBD2 scanner before purchasing replacement parts.
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