P0418 on Toyota
Secondary Air Injection System Relay A Circuit
P0418 on Toyota vehicles indicates secondary air injection system relay a circuit. Au7o has documented this code across 5 Toyota models — most commonly on 4Runner, Land Cruiser, Sequoia. 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. Typical repair costs on Toyota range from $100 to $4,000, depending on the specific model and root cause.
Common Causes of P0418
- •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
P0418 on Toyota by Model
Toyota 4Runner(1 issue)
- Secondary Air Injection Pump/Valve Failure Triggering Limp Mode on 4.7L V82005-2009
The 4.7L 2UZ-FE V8 used in later 4th-generation 4Runners is known for secondary air injection system failures involving the air pump and switching valves. When the system sticks or fails electrically, the truck may illuminate the check engine light and enter reduced-power or limp mode. This problem is widely documented across Toyota V8 trucks and SUVs of the era and can be very expensive when repaired with OEM components.
Toyota Land Cruiser(1 issue)
- Secondary Air Injection System Failure (100-Series, 4.7L V8)1998-2007
The secondary air injection (AI) system on the 100-series Land Cruiser (1998-2007) with the 2UZ-FE 4.7L V8 is a notorious failure point, identical to the issue on the Sequoia and Tundra of the same era. The electric AI pump, air switching valves (ASV), and exhaust manifold check valves all fail. The aluminum check valves in the exhaust manifolds corrode and seize, the ASV sticks from carbon buildup, and the pump motor eventually burns out. This system is responsible for the most common check engine light on 100-series Land Cruisers.
Toyota Sequoia(2 issues)
- Secondary Air Injection System Failure (2UZ-FE)2001-2009
The 4.7L 2UZ-FE's secondary air injection system fails due to corroded air switching valves (ASVs) and seized air pumps. Moisture enters the system and corrodes internal components. Causes check engine light with P2440/P2442 codes.
- Secondary Air Injection Pump Failure (3UR-FE/i-FORCE)2008-2019
2nd-gen Sequoias with the 5.7L 3UR-FE also suffer from secondary air injection pump failures, similar to the 1st gen but with updated part numbers. The pump seizes from internal moisture corrosion, triggering P2440-P2445 codes and check engine light.
Toyota Tacoma(1 issue)
- Secondary Air Injection Pump and Switching Valve Failure on 4.0L V62005-2011
Tacomas with the 1GR-FE 4.0L V6 are known for failures of the secondary air injection system, including the air pump and switching valves. Moisture intrusion and valve sticking can trigger check-engine lights and force the truck into reduced-power or limp mode. Owners frequently report sudden loss of acceleration along with expensive dealer repair estimates because the intake manifold often must be removed to access components.
Toyota Tundra(1 issue)
- Secondary Air Injection Pump Failure2005-2013
The secondary air injection pump is prone to failure due to water intrusion. The electric motor is located in the wheel well with moisture exposure, and the rubber boot covering the motor traps water, causing the pump to short circuit. This triggers check engine lights with codes P2440, P2443, P2445, P2447, P0418, or P0419. Some vehicles may enter limp mode.
Looking for P0418 on a different make?
View P0418 across all makes →Frequently Asked Questions
What does P0418 mean on Toyota?▼
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 Toyota specifically, this code is documented across 5 models.
What causes P0418 on Toyota vehicles?▼
Common causes on Toyota: 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. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0418 on a Toyota?▼
Repair costs on Toyota range from $100 to $4,000, depending on the specific model and root cause.
Which Toyota models have P0418 documented?▼
Au7o has documented P0418 on 5 Toyota models: 4Runner, Land Cruiser, Sequoia, Tacoma, Tundra.