OBDII Code List

P0135 MERCEDES-BENZ - O2 Sensor Heater Circuit Malfunction Bank 1 Sensor 1

Repair Importance Level: 2/3
Repair Difficulty Level: 2/3   
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Possible causes

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

Tech notes

Mercedes Benz Code = 0433 (Right O2 sensor, before TWC): Short circuit to positive / Resistance of sensor heater too low (P0135)
Mercedes Benz Code = 0436 (Right O2 sensor, before TWC): Heating capacity is too low. (P0135)

The code means that there is a problem with the heater element circuit of the heated oxygen sensor. The control module monitors how long it takes the sensor to warm up and start sending an adequate signal. The code is triggered when the sensor is taking too long to warm up. Water getting inside the heated oxygen sensor connector can be caused the heated oxygen sensor fuse to blow. Before replacing the sensor, check for the condition of the heated oxygen sensor fuse and connectors. If the sensor and connector are OK, replacing the O2 Sensor 1 usually takes care of the problem

When is the code detected?

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 heat

Possible symptoms

  • Engine Light ON (or Service Engine Soon Warning Light)
  • Possible higher than usual fuel Consumption

P0135 Mercedes-benz Description

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.

OBDII Code P0135 Mercedes-benz - O2 Sensor Heater Circuit Malfunction Bank 1 Sensor 1 -

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