Engine-Codes - Mercedes-benz - P0155 MERCEDES-BENZ

P0155 MERCEDES-BENZ - O2 Sensor Heater Circuit Malfunction Bank 2 Sensor 1

Repair Importance Level: 2/3
Repair Difficulty Level: 2/3  What is this?
Table of contents

P0155 MERCEDES-BENZ Possible Causes

  • Faulty Heated Oxygen Sensor (H2OS) Bank 2 Sensor 1
  • Heated Oxygen Sensor (H2OS) Bank 2 Sensor 1 circuit fuse
  • Heated Oxygen Sensor (H2OS) Bank 2 Sensor 1 harness is open shorted to ground
  • Heated Oxygen Sensor (H2OS) Bank 2 Sensor 1 circuit poor electrical connection
  • Faulty Engine Control Module (ECM)

How is the P0155 MERCEDES-BENZ code repair?

Start by checking the "Possible Causes" listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector's pins.

Tech Notes

Mercedes Benz Code = 0437 (Left O2 sensor, before TWC): Short circuit to positive / Resistance of sensor heater too low (P0155)
Mercedes Benz Code = 0440 (Left O2 sensor, before TWC): Heating capacity is too low. (P0155)

The code means that there is a problem with the heater element circuit of the heated oxygen sensor. The Engine Control Module (ECM) monitors how long it takes the sensor to warm up and start sending an adequate signal. The code means the sensor is taking too long to warm up. Replacing the Front Heated Oxygen Sensor (H2OS) Bank 2 usually takes care of the problem.

What is the cost to diagnose the P0155 MERCEDES-BENZ code

Labor: 1.0

The cost to diagnose the P0155 MERCEDES-BENZ code is 1.0 hour of labor. The auto repair's diagnosis time and labor rates vary by location, vehicle's make and model, and even your engine type. Most auto repair shops charge between $75 and $150 per hour.
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When is the code detected?

The current amperage in the front heated oxygen sensor heater circuit is out of the normal range. (An improper voltage drop signal is sent to ECM through the front heated oxygen sensor heater)

Possible Symptoms

  • Engine Light ON (or Service Engine Soon Warning Light)
  • Possible higher fuel consumption
  • Possible more smoke from exhaust than usual

P0155 MERCEDES-BENZ Meaning

Oxygen Sensors (O2S) or Heated Oxygen Sensors (HO2S) need to reach a minimum operating temperature of 750 degrees F to produce an accurate voltage signal. The faster the heated oxygen sensor reaches that temperature the faster the sensor will start sending an accurate signal to the Engine Control Module (ECM). In order to achieve the require temperature, a heater element is included inside the heated oxygen sensor. The ECM controls the heated oxygen sensor heater element based on signals from the engine coolant temperature and engine load. The ECM controls the heater element circuit by allowing current flow to ground.
This fault code is stored in the engine control module when the current flow through the oxygen sensor heater circuit is not as expected. The ECM uses a comparator to measure the voltage drop across a known resistor, using this value the system can calculate the current flow within the circuit. The supply voltage to the component must be investigated. The resistance of the heater element should also be tested. A resistance of approximately 8 Ohms to 15 Ohms is satisfactory. Due to the location of this component the electrical connector can become contaminated with splash from the road. Separate the electrical connector and inspect the pins for corrosion.

More Information

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