P0418 on Lexus: How to Diagnose & Fix
Secondary Air Injection System Relay A Circuit
1 Lexus model · 1 documented issue
P0418 on Lexus by model: symptoms, diagnosis and fix
The secondary air injection system pumps air into the exhaust on cold start to light the catalysts faster. On the GX 460 the failure starts at the pump. The foam filter inside the air injection pump disintegrates with age and the debris is drawn into the system, blocking the air switching valves and lines downstream. The Lexus campaign notice says moisture degrades this filter, and the damage then spreads to the air switching valves. Either failure sets emissions codes and drops the vehicle into limp mode, which owners experience as a sudden dramatic loss of power on a cold morning, usually on the first drive of the day. Lexus addressed the defect for 2010-2013 GX 460 vehicles with the 1UR-FE engine in technical bulletin L-SB-0028-14, covering MIL-on conditions with DTC P0418, P2440, P2442 and/or P2445, and in Special Service Campaign JLG, under which the pump filter and air switching valves are replaced at no charge with no year or mileage limit. This is the same architecture that troubles the 2010-2013 Tundra, Sequoia, and LX 570.
Common Symptoms
- Sudden loss of power and limp mode on cold start
- Check engine light with secondary air injection codes
- Loud whirring or buzzing from the engine bay on cold start
- Rough running for the first minute after a cold start
- Failed emissions test
How to Fix
Before paying for anything, check the VIN against Lexus Special Service Campaign JLG (repair procedure in bulletin L-SB-0028-14): for affected 2010-2013 GX 460 vehicles the dealer replaces the air injection pump filter with an improved-design part and replaces the air switching valves free of charge, and will replace the air injection pump itself as needed at no cost. Many owners pay several thousand dollars for this repair without ever learning the campaign exists, so make this call first. If the vehicle is outside the campaign, diagnose which half has failed before buying parts, because the pump and the valves are priced very differently. Pull the codes and inspect the pump's foam filter — if it has disintegrated, replacing valves alone guarantees a repeat failure because the debris is still in the system, so the lines must be cleared too. Bulletin L-SB-0028-14 replaces parts by code: P2440 calls for the Bank 1 valve plus the pump, P2442 for the Bank 2 valve plus the pump, and P0418 and/or P2445 alone for both valves plus the pump. Fit the improved-design filter so the failure does not recur. Some owners fit an aftermarket bypass or delete to escape the failure loop, but understand that this defeats an emissions control device, will fail inspection in most states, and is illegal to perform on a road vehicle.
Sources for this issue (4)
P0418 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0418 mean on a Lexus?
P0418 stands for "Secondary Air Injection System Relay A Circuit." This code means the Engine Control Module detected a fault in the control circuit for Secondary Air Injection (AIR) System Relay 'A'. The secondary air injection system pumps fresh air into the exhaust during cold starts to help the catalytic converter heat up faster and burn off pollutants, and Relay A switches power to that air pump. P0418 sets when the computer commands the relay but sees an abnormal voltage or no response on its control circuit. This is an emissions-related fault that may keep the air pump from running when needed. On Lexus it is documented across 1 model: GX.
What are the most common causes of P0418?
The most common causes of P0418 are: Faulty secondary air injection relay (Relay A), Open, shorted, or corroded relay control wiring, Poor power or ground feed to the relay, Failed secondary air injection pump (drawing wrong current), Corroded relay socket or connector, Blown fuse in the air injection circuit, Faulty ECM relay driver. The specific cause varies by vehicle.
How much does it cost to fix P0418 on a Lexus?
Repair costs vary widely with the root cause and Lexus model; each issue on this page carries its own estimate where one is published.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.