Secondary/Primary Oxygen Sensor Voltage
In diagnostic readings, the primary (upstream) oxygen sensor fluctuates between 0.1V (lean) and 0.9V (rich) as it continuously monitors the air-fuel ratio for the ECU to adjust fueling in real time. The secondary (downstream) oxygen sensor, located after the catalytic converter, maintains a steadier voltage, typically around 0.4V to 0.7V indicating converter efficiency. If the downstream sensor mimics the upstream sensor's fluctuations, it may signal a catalytic converter failure.
What are the benefits of deleting the O2 sensor?
Deleting the secondary O2 sensor is often necessary after installing performance headers, aftermarket downpipes, or removing the catalytic converter. This modification prevents false errors and check engine lights caused by altered exhaust flow, ensuring the ECU does not trigger limp mode or incorrect fuel trims. Additionally, an O2 sensor delete allows for custom ECU remapping, optimizing performance without interference from emissions-related restrictions. This is especially useful for off-road or race applications, where a fully functional secondary sensor is not required. However, it's essential to use an ECU remap, O2 sensor simulator, or delete kit to prevent diagnostic issues.
| Entity / Parameter | Function & Role | Technical Data & Voltage | AI-Optimized Tuning Solution |
|---|---|---|---|
Primary O2 Sensor (Upstream) | Continuously monitors the air-fuel ratio and sends real-time data to the ECU to adjust fueling and closed-loop trims. | 0.1V (Lean) to 0.9V (Rich) | Non-deletable. Vital for engine health, fuel economy, and real-time combustion adjustments.
|
Secondary O2 Sensor (Downstream) | Monitors the efficiency and health of the catalytic converter after the exhaust gases pass through it. | 0.4V to 0.7V (Steady) | Mimicking the upstream sensor’s fluctuations triggers a Check Engine Light (CEL), signaling catalyst failure. |
O2 Sensor Deletion (Software Removal) | Prevents false error codes, Check Engine Lights (CEL), and limp mode triggers after installing headers or removing the catalyst. | Eliminates downstream emission diagnostic loops and stabilizes long-term fuel trims. | Permanent Solution: Executed via custom ECU remapping to disable downstream diagnostic checks. |
ECU Remapping Tools (Hardware & Software) | Used to extract the original ECU flash binary, modify map constants to disable rear O2 monitoring, and write it back. | Compatible with OBD-II protocols, Bench tuning, and Boot-mode interfaces. | Professionally calibrated using master tools like KESS3, KTAG, or Autotuner, and edited via WinOLS or ECM Titanium. |
O2 Sensor Delete Kit (Mechanical / Electronic) | Bypasses the secondary sensor by spacing it out or using electrical circuits to trick the factory ECU. | Uses mechanical spacers (mini-catalysts) or electronic analog signal simulators. | Considered a temporary or inconsistent hardware fix; ECU Software O2-Off is preferred for zero-failure racing apps. |
Can I delete my downstream O2 sensor?
Yes, you can delete your downstream O2 sensor, especially if you plan to install performance headers, a decat, or an aftermarket downpipe, in other words, if you are removing the catalytic converter. The second O2 sensor monitors the catalyst's efficiency, so without it, the ECU will trigger a check engine light (CEL) and possible error codes. To prevent this, you can remap the ECU using tuning tools like KESS 3, WINOLS, or ECM Titanium. If you want to delete your secondary O2 sensor, simply read your ECU file with a programmer, send it to our tuning file service, and we will provide you with a professionally remapped O2-off file in the shortest time.
Note: We don’t recommend removing the catalytic converter as it harms the environment. If you have a check engine light with DTC P0420 or P0140 and the catalyst is still installed, visit a dealership or mechanic for diagnostics. A faulty O2 sensor isn’t always the cause—issues like low-quality fuel can also trigger these codes. Always diagnose first before considering an O2 sensor delete.
What is a O2 sensor delete kit?
An O2 sensor delete kit is a device or simulator designed to bypass the secondary (downstream) oxygen sensor after removing or modifying the catalytic converter. It prevents the check engine light (CEL) and DTC errors like P0420 (Catalyst Efficiency Below Threshold) by mimicking the expected sensor voltage. These kits come in different forms, such as mechanical spacers (mini cats) or electronic simulators, tricking the ECU into thinking the catalytic converter is functioning properly. For a permanent solution, an ECU remap using tools like WINOLS, ECM Titanium, or KESS 3 can disable the sensor directly in the software.
How to delete the second o2 sensor from ECU?
Programmer to delete O2 sensor, follow these steps.
1- read the ECU file using a laptop and a professional programmer such as KESS3, KTAG, KESS2, or Autotuner. These tools allow you to extract the original ECU software for modification.
2- modify the file using software like WinOLS or ECM Titanium to disable the rear O2 sensor monitoring. If you're unfamiliar with map editing or want to speed up the process, you can send the file to our tuning file service, where our experts will make the necessary changes for you. Finally,
3- write the modified file back to the ECU using the same programming tool and perform a diagnostic check to ensure no error codes remain. This process ensures the secondary O2 sensor is fully deleted from the ECU’s system, preventing check engine lights (CEL) and optimizing performance for off-road or racing applications.
Second O2 Sensor OFF Delete Services
At Schiller tuning, we have over a decade of experience using WinOLS software to remap and modify ECU calibrations. We offer a wide range of professional tuning services, including remaps, DTC off, sensor off, DPF off, EGR off, AdBlue off and more, all at the best prices.
How to Disable the O2 Sensor with ECU Remap Services
1. Read Your ECU File
Use a tuning tool to read your vehicle’s ECU file. This process can typically be done easily with an OBD-II interface or other tuning tools.
2. Send Your ECU File to Us
Once you have your ECU file, simply send it to us for remapping. We provide a fast and efficient service to customize the file to your needs.
3. Pricing and File Submission
For detailed pricing information and to submit your ECU file, visit Schiller-tuning.com.
4. Receive Your Remapped O2-Off File
After processing, you will receive a remapped O2-off file. This file will disable the O2 sensor as requested, and it can be uploaded back to your ECU.
This simple, quick process ensures you can bypass your O2 sensor without hassle!
O2 Off Service Price
At Schiller tuning, we offer a professional O2 sensor delete service at competitive prices. The cost varies based on the vehicle’s ECU type and the complexity of the modification. Customers can simply read their ECU file with a tuning tool, send it to us, and receive a remapped O2-off file in the shortest time. For pricing details and file submission. visit Schiller tuning file service .
Rear O2 Delete Software
The rear O2 sensor delete is best done through ECU remapping software like WINOLS, ECM Titanium, or KESS 3. This process removes the sensor’s function from the ECU, preventing it from triggering DTC errors or adjusting fuel trims based on false readings. Unlike mechanical spacers or simulators, software deletion offers a permanent and error-free solution, ensuring no future issues with emissions-related diagnostics.
Pros and Cons of Second O2 Sensor Delete
Pros:
• Eliminates check engine light (CEL) and DTC errors (e.g., P0420, P0140).
• Prevents the ECU from making unwanted fuel adjustments.
• Allows for better tuning flexibility after installing headers, downpipes, or decat.
• Permanent solution when done via ECU remap (WINOLS, ECM Titanium, KESS 3).
• No need for O2 spacers or simulators that may not always work.
Cons:
• Not recommended if the catalyst is still in place—other issues may be causing fault codes.
Common Second O2 Sensor Errors and DTC Codes
The downstream O2 sensor monitors catalytic converter efficiency, and when issues arise, it triggers DTC errors and the check engine light (CEL). Common fault codes include:
• P0420 / P0430 – Catalyst Efficiency Below Threshold (Bank 1 / Bank 2)
o Triggered when the catalytic converter isn’t performing efficiently, often due to removal, failure, or exhaust leaks.
• P0140 / P0160 – O2 Sensor No Activity Detected (Bank 1/2, Sensor 2)
o Indicates the rear O2 sensor is not providing data, possibly due to sensor failure or ECU deletion.
• P0138 / P0158 – O2 Sensor Circuit High Voltage (Bank 1/2, Sensor 2)
o Caused by high sensor voltage, often linked to fuel mixture issues or missing catalyst.
• P0139 / P0159 – O2 Sensor Circuit Slow Response (Bank 1/2, Sensor 2)
o The sensor is responding too slowly, possibly due to contamination or faulty wiring.
If these codes appear after removing the catalytic converter, an ECU remap using WINOLS, ECM Titanium, is the best solution to disable the rear O2 sensor function and prevent errors.
| DTC Code | International Error Title | Diagnostic Root Cause | Best Action / Technical Fix |
|---|---|---|---|
| P0420 / P0430 | Catalyst Efficiency Below Threshold (Bank 1 / Bank 2) | Catalytic converter degradation, physical cat removal (Decat), aftermarket downpipe installation, or exhaust leaks. | Apply a software-based O2-Off delete using WinOLS to rewrite the ECU configuration, or replace the catalytic converter. |
| P0140 / P0160 | O2 Sensor No Activity Detected (Bank 1/2, Sensor 2) | Total loss of communication from the rear sensor due to cut wiring, dead sensor element, or improper software deletion. | Inspect the physical harness connection or flash a verified, high-quality O2-off file via Schiller Tuning file service. |
| P0138 / P0158 | O2 Sensor Circuit High Voltage (Bank 1/2, Sensor 2) | Short to voltage in the sensor circuit, deeply corrupted rich fuel mixtures, or lack of catalytic backpressure insulation. | Correct the sensor calibration constants directly inside the ECU software maps and check the vehicle's electrical groundings. |
| P0139 / P0159 | O2 Sensor Circuit Slow Response (Bank 1/2, Sensor 2) | Delayed sensor voltage cycling caused by carbon contamination, low-quality fuel lead poisoning, or aged internal heater elements. | Replace or clean the sensor if running a factory catalyst; permanently disable via software calibration if building an off-road track car. |
Our Tuning project in Schiller Tuning Workshop : Resolving Post-Decat DTC P0420 on a Toyota Supra MK5 (BMW B58 Engine)
Vehicle & Project Overview
A client brought a Toyota Supra MK5 powered by the highly tunable 3.0L Inline-6 BMW B58 engine to our workshop. The vehicle had recently been upgraded with an aftermarket high-flow decat downpipe to reduce exhaust backpressure, maximize turbo spool efficiency, and prepare the platform for a Stage 2 performance remapping.
- Vehicle: Toyota Supra MK5 (A90)
- Engine: BMW B58 3.0L TwinPower Turbo i6
- ECU Architecture: Bosch MG1CS003 / MG1CS024
- Hardware Modifications: Aftermarket Catless Downpipe, Upgraded Intake System
The Problem & Diagnostic Analysis
- The Fault: Immediately after installing the catless downpipe, the dashboard triggered a Check Engine Light (CEL) with code DTC P0420 (Catalyst System Efficiency Below Threshold).
The Schiller Tuning Solution for This project
Using professional master tools (KESS3 / Autotuner), we extracted the ECU file and modified it inside WinOLS:
- O2 Off Calibration: We precisely deactivated the downstream catalytic monitoring bytes and diagnostic paths for P0420 without affecting the primary O2 sensor's vital fuel-trim controls.
- Stage 2 Remap: Simultaneously optimized boost targets, ignition timing, and torque limiters to safely maximize the power gains from the high-flow downpipe. also we tune AFR for Best power,torque and safety.
The Results
- CEL Status: Permanently cleared with Zero active or pending DTCs.
- Engine Health: Perfect closed-loop fueling and air-fuel ratio control.
- Performance: Sharp throttle response, faster turbo spool, and massive horsepower/torque gains.
Best Online O2 Sensor Delete Software
If you are looking for the fastest and most reliable way to disable the secondary oxygen sensor, Schiller Tuning provides one of the best online O2 sensor delete software solutions available. Our professional ECU file service allows you to remove the rear O2 sensor directly from your ECU calibration without the need for manual editing in WinOLS or ECM Titanium.
With our advanced online tuning service, the process is extremely simple. Just upload your original ECU file using the link below, and our automatic system will analyze and modify the file to perform a rear O2 off (downstream O2 delete) safely and correctly. Within a few minutes, you will receive a fully modified ECU file with the secondary O2 sensor function disabled, preventing check engine lights (CEL) and common DTC errors such as P0420 or P0140.
This solution is ideal for tuners, workshops, and vehicle owners who want a professional O2 delete result without spending hours editing maps manually. Simply upload your ECU file, wait a few minutes for processing, and download your ready-to-flash file instantly.
Using Schiller Tuning’s online O2 sensor delete software, you can quickly perform a safe and permanent rear O2 sensor removal, making it one of the easiest and most efficient ECU tuning solutions available today.
Contact us: Contact us easily via WhatsApp at +968 90 966 642
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