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The diagnostic trouble code P0135:20 refers to a malfunction in the heated exhaust oxygen sensor (HO2S) heater circuit for the right upstream sensor (sensor 1). This code indicates that there is an issue with the electrical circuit responsible for heating the oxygen sensor.

The heated oxygen sensor plays a crucial role in monitoring the oxygen content in the exhaust gases. The sensor’s heater circuit helps to bring the sensor to the optimal operating temperature quickly for accurate readings.

Here are some possible causes and solutions for this issue:

1. Faulty oxygen sensor: The first step is to check the condition of the oxygen sensor itself. The sensor may be malfunctioning and require replacement. Consult the vehicle’s service manual or a professional mechanic for the exact location and replacement procedure of the right upstream oxygen sensor.
2. Wiring or connector problems: Inspect the wiring harness and connectors associated with the HO2S heater circuit. Look for any signs of damage, such as frayed wires, loose connections, or corrosion. Repair or replace any damaged wiring or connectors as needed.
3. Check the fuse: There may be a blown fuse that is affecting the HO2S heater circuit. Locate and inspect the fuse related to the oxygen sensor heater circuit. If the fuse is blown, replace it with a new one of the appropriate rating.
4. Test the circuit: Use a multimeter or a diagnostic tool to test the HO2S heater circuit for continuity and proper voltage. Follow the manufacturer’s guidelines or consult a professional mechanic for specific instructions on how to perform this test. If the circuit is not functioning correctly, further diagnosis may be required to identify the root cause.
5. Check the engine control module (ECM): In some cases, the issue may lie with the ECM, which controls the operation of the oxygen sensor heater circuit. A malfunctioning ECM may not be providing the necessary voltage or signal to properly heat the sensor. Consult a professional mechanic or dealership to perform further diagnostics and potentially reprogram or replace the ECM if necessary.

It is important to note that these are general suggestions, and the specific diagnostic and repair procedures may vary depending on the make, model, and year of your vehicle. If you are unsure or uncomfortable performing these steps yourself, it is recommended to seek assistance from a qualified mechanic or dealership. They will have the necessary expertise and tools to accurately diagnose and resolve the issue with the HO2S heater circuit.