22836 Denso Lambda sensor/Air Fuel Ratio Sensor 2345178

Denso Air Fuel Ratio Sensor / Lambda Sensor 234-5178

Ensure precise air-fuel mixture control and optimal engine management with the Denso Air Fuel Ratio Sensor 234-5178 (SKU 22-836). This premium OEM-quality wideband lambda sensor is engineered by Denso to accurately measure the oxygen content of exhaust gases across a wide range of air-fuel ratios, providing the engine control unit (ECU) with critical real-time feedback for precise fuel injection control, optimal combustion efficiency, and reduced emissions. Designed specifically for the Subaru Forester and WRX with the FA20E engine, this sensor ensures dependable engine management performance and long service life.

CLICK HERE TO CHECK IF THIS FITS YOUR VEHICLE.

Key Features & Benefits

• Denso OEM Quality - Trusted OEM supplier component built to exacting standards
• Subaru Forester & WRX FA20E Application - Designed specifically for the FA20E engine
• Wideband Lambda Measurement - Accurately measures oxygen content across a wide AFR range
• Precise Fuel Trim Control - Enables the ECU to maintain the correct air-fuel ratio under all conditions
• Improved Fuel Economy - Supports accurate closed-loop fuelling for maximum efficiency
• Reduced Emissions - Ensures correct catalytic converter operation and low exhaust emissions
• Fast Light-Off - Integrated heater circuit reaches operating temperature quickly after cold start
• Direct OEM Replacement - Engineered to original specifications
• Long Service Life - Durable construction for extended reliability

Technical Specifications

• Denso Part Number: 234-5178 (2345178)
• SKU: 22-836
• Component Type: Air Fuel Ratio Sensor / Wideband Lambda Sensor (upstream O2 sensor)
• Primary Application: Subaru Forester FA20E, Subaru WRX FA20E
• Weight: 0.2 kg (approximate)

Vehicle Compatibility

This Denso air fuel ratio sensor is designed for the following models:

• Subaru Forester — FA20E engine
• Subaru WRX — FA20E engine

Always verify fitment for your specific vehicle, model year, and sensor position before ordering.

CLICK HERE TO CHECK IF THIS FITS YOUR VEHICLE.

OEM Part Number Cross-Reference

This Denso air fuel ratio sensor replaces the following OEM part numbers:

• 234-5178 (Denso)
• 22641AA650 (Subaru)
• EGO-836 / EGO836

Common Symptoms of a Faulty Air Fuel Ratio Sensor

• Check engine light illuminated on dashboard
• O2 or AFR sensor fault codes (P0130–P0167, P2195–P2199)
• Poor fuel economy or rich/lean running condition
• Black smoke from exhaust (rich) or popping/lean surge
• Rough idle or engine hesitation
• Failed emissions test
• Catalytic converter damage from incorrect AFR over time
• Slow or erratic fuel trim corrections
• Increased fuel consumption

What Does an Air Fuel Ratio Sensor Do?

The air fuel ratio sensor (AFR sensor), also known as a wideband lambda sensor or upstream oxygen sensor, is a critical engine management component mounted in the exhaust system before the catalytic converter. Unlike a conventional narrowband oxygen sensor that simply switches between rich and lean signals, the wideband AFR sensor can measure the precise air-fuel ratio across a wide range (typically 10:1 to 20:1 AFR), providing the ECU with detailed, linear feedback about combustion quality. The ECU uses this signal to continuously adjust fuel injection pulse width in real time, maintaining the target stoichiometric air-fuel ratio (14.7:1 for petrol) for optimal combustion efficiency, fuel economy, and emissions control. An integrated ceramic heater element brings the sensor to operating temperature rapidly after cold start, enabling closed-loop fuel control to begin within seconds of engine startup. A faulty AFR sensor causes the ECU to rely on default fuel maps, resulting in poor fuel economy, emissions failures, and potential catalytic converter damage.

Why Choose Denso Air Fuel Ratio Sensors?

Denso is one of the world's largest and most trusted OEM automotive component suppliers, and is the original manufacturer of oxygen and air fuel ratio sensors for many major vehicle brands including Subaru, Toyota, and Honda. Denso AFR sensors are engineered to exacting OEM specifications with precision ceramic sensing elements, high-quality heater circuits, and durable construction for long service life in demanding exhaust environments. Choosing a Denso air fuel ratio sensor ensures accurate AFR measurement, reliable ECU feedback, and the confidence of genuine OEM-equivalent quality.

Installation Notes

Professional installation is recommended for best results. Air fuel ratio sensor replacement requires allowing the exhaust system to cool completely before starting work to avoid burns. Use a dedicated oxygen sensor socket for removal. Apply anti-seize compound to the threads of the new sensor if not pre-applied, taking care not to contaminate the sensor tip. Torque the new sensor to manufacturer specifications — do not overtighten. Reconnect the electrical connector and ensure the wiring harness is routed away from hot exhaust components. Clear any diagnostic trouble codes and allow the engine to complete a full drive cycle to enable the ECU to perform fuel trim adaptation with the new sensor. Verify no fault codes return after the drive cycle.

Why Choose LM15 Motorsport?

We supply quality OEM and OEM-equivalent engine management components with fast shipping across Australia. Every air fuel ratio sensor is carefully inspected to ensure you receive the correct component for reliable engine management performance. Our team has extensive experience with Subaru FA20E engines and can provide expert advice on oxygen sensor diagnosis and replacement.

Need help with fitment or installation? Contact our expert team for advice specific to your Subaru Forester or WRX FA20E air fuel ratio sensor requirements.