P0155 Code: Meaning, Symptoms, Causes & Fixing

The latest vehicle contains an oxygen sensor that monitors the entry of the exhaust gases in the engine. This sensor contains a heating element. The powertrain control module (PCM) uses the information of the O2 sensor to adjust the air-fuel ratio. When your PCM detects a fault in the heater circuit of the O2 sensor, it triggers the P0155 code. This article mainly explains the P0155 code symptoms, its causes, and how to fix it.  

P0155 Code Definition

P0155 code stands for “O2 Sensor Heater Circuit Malfunction (Bank 2, Sensor 1).”

What Does the P0155 Code Mean?

The P0155 trouble code is triggered when the powertrain control module (PCM) monitors a short in circuit or excessive resistance in the heater circuit of your vehicle’s Bank 2 heated oxygen sensor.

P0155 code

The oxygen (O2) sensor plays a vital role in ensuring the efficient performance of your vehicle engine. The heating circuit of the O2 sensor (Bank 2 Sensor 1) is installed just before the catalytic converter in the exhaust manifold.

The heated oxygen sensor (HO2 sensor) is also known as the AF sensor or O2 sensor. The main function of the oxygen sensor is to monitor the level of O2 just before exhaust gases enter the catalytic converter. It sends this data to your vehicle’s powertrain control module (PCM).

The PCM utilizes the information of the upstream oxygen sensor to adjust the air/fuel ratio of your engine up to the optimal level (approximately 14.7:1).

The O2 sensor of your vehicle also contains a heating element that assists it in achieving the operating temperature rapidly, minimizing the time spent in open-loop operation.

Your PCM triggers the diagnostic trouble code P0155 when it tests the heater circuit of the Bank 2 upstream heated oxygen sensor and monitors excessive resistance or a short in the heater circuit.

 P0155 Code Causes

  • Damaged or bad Bank2 upstream heated oxygen sensor
  • Blown Fuse
  • Damaged or corroded connections or wires
  • Insufficient battery voltage or dead battery
  • Short or open HO2S heater power (12v) circuit
  • Bad spark plug 
  • Opened heated oxygen sensor ground circuit
  • Faulty engine coolant temperature (ECT) sensor
  • Damaged HO2S connector
  • Damaged or faulty PCM
  • Hose is not connected to the EGR system module

P0155 Code Symptoms

  • Poor fuel economy
  • Illuminated check engine light
  • Rough idle
  • Strong smell like rotten egg coming from the tailpipe
  • Engine is shutting off infrequently
  • Black smoke coming from the exhaust

How to diagnose the P0155 Code?

  • Ensure the existence of the P0155 code by using an OBD-II scanner
  • Collect the data stored in the power control module (PCM) memory.
  • Clear the codes and perform a test drive. If the P0155 code is triggered again, inspect all the vital parts.
  • Inspect the metal tabs, wire harnesses, and electrical connections for damage.
  • Inspect the wiring to the O2 sensor for damage.
  • Use a multimeter to test the oxygen sensor for proper voltage.
  • Properly inspect the engine coolant temperature sensor for fault.
  • Check the engine ground for corrosion or loose connection
  • Inspect the spark plug for damage.
  • Inspect the fuse. If it is blown, replace it.
  • Check the voltage of your vehicle battery.
  • Inspect the PCM of your vehicle. Update the PCM software if needed.

 Common P0155 Code Diagnostic Mistakes 

  • Replacing the HO2 sensor before properly checking the other parts
  • Replacing the O2 sensor without inspecting the electrical connections and wires
  • Not erasing the PCM/ECM memory after fixing the problem

What repairs can fix the P0155 Code

  • Replacing the faulty spark plug
  • Replacing the faulty Bank2 O2 sensor
  • Repairing or fixing the damaged electrical wires
  • Fixing the loose the connections
  • Replacing the blown fuse
  • Replacing the bad coolant temperature sensor
  • Fixing the open HO2S heater ground circuit
  • Fixing the issues related to the PCM

Repair Costs for P0155 Code

To fix the P0155 code, you need one or more of the below-given repairs:

PartsRepair Cost
Fuse replacement$8 to $15
Oxygen sensor replacement$180 to $310
Wires replacement$90 to $1100

FAQ Section

How serious is the P0155 code?

The severity level of the P0155 is moderate. This trouble code may cause various drivability issues, such as poor fuel economy and rough idle. This code doesn’t produce immediate issues but indicates that the engine is not reaching the proper operating temperature. This code is directly related to engine operating temperature issues. Therefore, when your vehicle triggers this code, you should immediately contact a professional to fix the issue.

If your vehicle is not set to closed-loop mode, you shouldn’t run your vehicle because driving in such a condition may put extra stress on various components, such as the camshaft, valve, and piston. Therefore, when your PCM triggers the P0155 code, you should immediately contact a mechanic to prevent your engine from damage.

What does Bank 1 or sensor 1 mean?

Sensor 1 indicates the first oxygen sensor installed in the exhaust system before the catalytic converter, while Bank 1 indicates the side of the engine that has cylinder number 1.

Can I drive with a P0155 Code?

Yes, you can drive with the P0155 code, but it is not recommended to drive with this code. This code is a strong indication that your engine is not working at normal operating temperatures. It generates different drivability issues, such as rough idle and poor fuel economy. Driving with this code may lead to the complete failure of the engine. Therefore, when your car triggers the P0155 code, you should immediately contact a professional.

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