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)

Tech notes

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 take the sensor to warm up and start sending an adequate signal. The code means the the sensor is taking too long to warm up. Replacing the Front Heated Oxygen Sensor (H2OS) Bank 2 usually takes care of the problem.

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)

Symptoms

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

P0155 FORD 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. The ECM monitors the voltage signal received through the heater element circuit and determines the state of the circuit by comparing the voltage detected with the factory specifications.

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FORD Technical Service Bulletins for P0155 code