P0135 Code: Symptoms, Causes, Repair Cost (& How to Fix it)

Your vehicle’s powertrain control module (PCM) is connected to multiple engine sensors. It takes data from these sensors to ensure the efficient working of your vehicle engine. Your PCM triggers the P0135 code when the heating circuit in the air-to-fuel ratio sensor goes bad. This trouble code may also indicate damaged wiring, poor connection, or a bad fuse of the heat circuit sensor. This article mainly explains the P0135 code symptoms, causes, and how to fix it. 

P0135 Code Definition

P0135 code stands for “Oxygen Sensor Heater Circuit Malfunction (Bank 1, Sensor 1).” 

What does the P0135 Code Mean?

The P0135 code indicates that the heater current of the heated oxygen sensor (HO2S) at Bank 1 is lower or higher than the ideal amp for a specific amount of time.

In the definition, Bank 1 indicates the side of the engine that contains the cylinder number. 1 and “sensor 1” indicates the upstream oxygen sensor.

P0135 Code

The latest vehicle contains O2 sensors. These sensors are used to regulate the air-fuel ratio in the intake system.

The oxygen (O2) sensors usually have a heating element to preheat the sensor during cold start situations. This heating element speeds up the process of bringing the O2 sensor temperature up to the normal operating temperature.

When the temperature of your engine coolant falls below a certain temperature range, the powertrain control module (PCM) turns on the O2 sensor heater. Your PCM will continue to supply voltage to the heating element until it reaches closed-loop (automatic) operation.

As your O2 sensor notices the engine has reached optimal working temperature, the fuel ratio is decreased to adjust fuel economy and reduce emissions.

When your PCM detects a delay between start-up and sensor activity, it assumes an issue with the heater circuit and triggers code P0135.

Causes of the P0135 Code

  • Bad Heated Oxygen Sensor (HO2S) connector
  • Bad coolant temperature sensor
  • Damaged catalytic converter
  • Faulty oxygen sensor
  • Damaged or corroded wiring on the O2 sensor
  • Excessive exhaust leaks
  • Problems with the power control module (e.g., outdated software)
  • Vacuum leak
  • HO2S heater low control circuit is open
  • HO2S ignition circuit is open
  • Low fuel pressure
  • A compromised HO2S heater element

Symptoms of the P0135 Code

  • Illuminated check engine light
  • The engine doesn’t operate as smoothly during start-up
  • Poor fuel economy
  • Poor engine performance
  • Rough idle on start
  • Black smoke from the exhaust pipe

Read More: P0053, P0054, P0123, P0102, P0122, P0123, P0134

How to diagnose the P0135 Code?

You need the following tools to fix or diagnose the P0135 code:

  • Vehicle-specific repair manual
  • Multimeter
  • OBD-II scanner
  • Basic hand tools

Follow the below-given steps to diagnose the P0135 code:

  1. Use an OBD-II scanner to find the code.
  2. Record all stored fault codes, along with all available freeze frame data. This information could be very helpful if an intermittent fault is diagnosed later on.
  3. Use a multimeter to check the O2 sensor voltage. Check your vehicle’s manufacturer manual to find the harness connector for the Bank 1 sensor 1 O2 sensor. For this step, follow the instructions written in the manufacturer’s manual. If no power is getting to the O2 sensor, inspect the fuse associated with that circuit. 
  4. Visually inspect the wirings and connections connected to the bad sensor. Use the manufacturer’s manual to find the location, color-coding, function, and routing of all wires in the circuit, and check for broken, damaged, burnt, or shorted connectors and wiring.
  5. If you couldn’t find any problem in the above-given steps, then it is definitely a problem with your bank 1 sensor 1 O2 Inspect your O2 sensor and replace it.

Diagnosis Mistakes of P0135 Code

  • Prematurely replacing the 02 sensors without inspecting other parts.
  • Replacing the O2 sensor without properly inspecting the system for the exhaust leak and vacuum leak.
  • No scanning of the new oxygen sensor to ensure the efficient working of the heater circuit
  • No inspection of the oxygen sensor wire harness for water entry into the harness cover
  • No inspection of the oxygen sensor for oil or other contaminants.
  • Improper diagnosis of the PCM.
  • Replacing any parts before you’ve done a thorough visual inspection and checked all wiring with a multimeter.

What repairs can fix the P0135 Code?

  • Repairing or replacing the bad oxygen sensor
  • Fixing the vacuum leaks
  • Repairing or replacing the damaged or corroded wirings to the oxygen sensor
  • Fixing the exhaust leaks
  • Replacing or repairing the connection to the oxygen sensor
  • Replacing the blown fuse to the heater circuit
  • Replacing or repairing the bad heater circuit to the bank 1 sensor 1 O2 sensor.
  • Replacing or reprograming the PCM

Repair Costs for P0135

The fixing cost of the P0135 code varies according to the vehicle model, labor cost, and repair cost of the relevant part. To fix or repair the P0135, you may need one or more of the following repairs:

Exhaust Leak repair$80 to $820
PCM replacement$1100 to $1400
Oxygen Sensor replacement$150 to $510
Wiring short repair$20 to $510

FAQ Section

How serious is the P0135 Code?

The P0135 error code is not a serious issue. You can drive your vehicle with this code and don’t need to make repairs immediately. However, this issue can lead to poor engine performance, poor fuel economy, and higher emissions. Therefore, you should fix it as soon as possible.

Is there a fuse for the oxygen sensor?

Yes, your vehicle has a fuse for the O2 heaters.

What side of the vehicle is Bank 1?

Bank 1 indicates the side of the engine that contains the cylinder number. 1.

Can I drive with a P0135 code?

Yes, you can drive with a P0135 code. This code is not considered a much serious code. However, if you drive with this code, you may face minor issues such as poor fuel economy and higher emissions.

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