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CEL with P0135 on 2017 S550 - O2 Sensor Heater Circuit

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Kevin B. · rep 0 · May 22, 4:16 AM · 1 replies · solved · Question

Vehicle: 2017 Mercedes-Benz S550 Sedan

Hey everyone, my Check Engine Light just came on in my 2017 Mercedes-Benz S550 Sedan. I pulled the code with my OBD-II scanner, and it's P0135. This code points to an O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1). The car feels a little sluggish, and I'm worried about fuel economy and potential emissions issues.

Is this a common issue for the S-Class, specifically the 2017 S550? I know O2 sensors can go bad, but the 'heater circuit' part makes me wonder if it's more than just a simple sensor replacement. Can I replace the sensor myself, or is it a job best left to a professional due to access or specific tools? Any advice on troubleshooting or specific parts to look for would be greatly appreciated.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:16 AM

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ClearTheCode admin answer:

The P0135 code for an O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1) on your 2017 Mercedes-Benz S550 is a common diagnostic trouble code that indicates an issue with the heating element within the oxygen sensor. Here's what you need to know:

  1. Understanding the O2 Sensor Heater Circuit:

    • Oxygen sensors need to reach a specific high temperature to accurately measure oxygen content in the exhaust gases. The heater circuit rapidly brings the sensor up to operating temperature, especially during cold starts.
    • Without the heater, the sensor takes much longer to become active, leading to inaccurate fuel mixture readings, increased emissions, and potentially poor fuel economy and engine performance (which aligns with your 'sluggish' feeling).

  2. Common Causes for P0135:

    • Faulty O2 Sensor: The heating element inside the sensor can burn out or fail. This is the most common cause.
    • Wiring Issue: Damaged, corroded, or shorted wiring to the O2 sensor's heater circuit can prevent it from receiving power.
    • Blown Fuse: A dedicated fuse for the O2 sensor heater circuit might be blown. Check your owner's manual for fuse box locations and diagrams.
    • ECM/PCM Issue: Less common, but a fault in the Engine Control Module (ECM) or Powertrain Control Module (PCM) that controls the heater circuit can also trigger this code.

  3. Troubleshooting Steps:

    • Visual Inspection: Check the O2 sensor's wiring harness for any signs of damage, fraying, or corrosion. Ensure it's securely plugged in.
    • Fuse Check: Locate and inspect the fuse(s) related to the O2 sensor heater circuit. Replace if blown.
    • Multimeter Test (Advanced): A technician can test the resistance of the heater circuit within the O2 sensor and check for voltage supply to the sensor's heater wires.

  4. Replacement Difficulty:

    • Replacing an O2 sensor can range from moderately easy to challenging depending on its location and access. Bank 1 Sensor 1 is typically the upstream sensor on the side of the engine containing cylinder #1 (driver's side on a V8).
    • You'll need a specialized O2 sensor socket, which is a deep socket with a slot for the wiring. Access can be tight on an S550, potentially requiring removal of other components.

  5. When to See a Shop:

    • If you're not comfortable working with exhaust components or electrical wiring, or if a simple fuse check doesn't resolve the issue, it's best to take your S550 to a qualified mechanic or Mercedes-Benz specialist.
    • They can accurately diagnose whether it's the sensor itself, the wiring, or another component, and ensure the correct OEM-quality sensor is installed and torqued properly.
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