The RF M18 x 1.5mm Mini Cat (Cat Fooler) is a small but highly effective exhaust component designed for modified vehicles—particularly those running decat pipes or high-flow catalytic converters. While it may look like a simple threaded fitting, it plays a crucial role in maintaining ECU harmony when factory emissions components are altered.
What This Product Actually Does
Modern vehicles rely heavily on oxygen (O2) sensors to monitor exhaust gases and ensure the catalytic converter is functioning efficiently. When you remove or upgrade your catalytic converter, the system often detects abnormal readings and triggers check engine lights (CEL)—typically codes like P0420 or P0430.
The Mini Cat solves this problem by:
- Relocating the downstream O2 sensor slightly out of direct exhaust flow
- Filtering exhaust gases through a mini catalytic substrate inside the spacer
- Sending a “normal” reading back to the ECU, even on modified setups
In simple terms:
It “fools” your car into thinking the catalytic converter is still working properly.
Key Features & Specifications
- Thread Size: M18 x 1.5 (standard O2 sensor fitment)
- Material: Stainless steel construction for durability
- Type: O2 sensor spacer with internal mini catalytic converter
- Fitment: Direct bolt-on (no welding required)
- Compatibility: Works with most vehicles using standard O2 sensors
How It Works (Simple Explanation)
1. Standard Setup (Problem)
When you remove a catalytic converter:
- Exhaust gases become “dirtier”
- The rear O2 sensor detects this
- ECU triggers a fault code and warning light
2. With a Mini Cat Installed
- The sensor is moved slightly away from the exhaust stream
- Gas passes through a mini catalytic element inside the spacer
- The reading appears cleaner and within expected parameters
- The ECU reads: “All good here”
This clever mechanical workaround avoids the need for ECU remapping or tuning in many cases.
Common Use Cases
This product is widely used in:
Decat Builds
- When the main catalytic converter is removed for performance gains
- Prevents constant CEL warnings
High-Flow Exhaust Systems
- Helps stabilise readings when using performance cats
Modified Street Cars
- Ideal for enthusiasts who want performance without dashboard errors
Track or Show Cars
- Especially useful where emissions hardware is altered but drivability matters
Benefits
Eliminates Check Engine Lights
Targets common fault codes like P0420/P0430 caused by inefficient catalyst readings.
No ECU Tuning Required
A plug-and-play solution that saves time and cost compared to remapping
Easy Installation
Simply screws into the existing O2 sensor bung
Durable Construction
Stainless steel ensures longevity under high exhaust temperatures
Cost-Effective Fix
A small investment compared to diagnostics, tuning, or replacing catalytic converters
Limitations (Important to Know)
This isn’t a miracle fix for every scenario:
- It may not solve all CEL issues (only catalyst-efficiency related ones)
- Some vehicles with very sensitive ECUs may still trigger codes
- You may need to reset the ECU after installation for best results
- It does not replace emissions compliance—it’s a workaround, not a legal substitute for a catalytic converter
Who Should Buy This?
This product is perfect for:
- Performance enthusiasts running decat systems
- Anyone tired of persistent check engine lights after exhaust mods
- Builders who want a clean dashboard without ECU tuning
- Workshops needing a quick, reliable solution for O2-related faults
Final Verdict
The RF M18 Mini Cat / Cat Fooler is one of those small components that delivers massive practical value in the performance world. It’s simple, affordable, and effective—bridging the gap between performance upgrades and ECU compatibility.
If you’re modifying your exhaust system and don’t want your dashboard lighting up like a Christmas tree, this is one of the easiest solutions available.
