Home
Estimates Trouble Codes P0135

P0135: O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)

Our mobile mechanics can quickly diagnose a P0135 trouble code and bring the shop to you 7 days a week. Get a quick and fair quote today.

Get a Quote

Find Your Cost

Delivery van
4.9
(1,013 Reviews)
4.5
(987 Reviews)
4.8
(2,074 Reviews)

What is P0135?

DTC P0135 (Diagnostic Trouble Code P0135) is defined as “O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)”.

It occurs when the Powertrain Control Module (PCM) or Engine Control Module (ECM) tests the oxygen sensor heater circuit in Bank 1 and detects a problem. Here, ‘Bank 1 Sensor 1’ refers to the upstream oxygen sensor located closest to the engine on the side with cylinder #1.

Without a functional oxygen sensor or heater element, the PCM or ECM won’t adjust the engine’s fuel injectors to maintain an air-fuel balance for each combustion cycle. As a result, the engine will run rich and affect your vehicle’s fuel efficiency. 

This problem is more common in older vehicles and is typically triggered by a short circuit or excessive resistance in the heater circuit.

Common symptoms

The P0135 code doesn’t have many obvious symptoms, but here’s what you may notice:

  • Reduced fuel economy (high fuel consumption): If the upstream O2 sensor is faulty, it’ll misread the oxygen levels and cause the PCM or ECM to deliver excess fuel to the engine.
  • Engine heats up slowly: The heated oxygen sensor malfunction causes the engine to heat up slower than usual, leading to a rough or idle start. This happens because the O2 sensor heater doesn’t output a voltage signal to the ECM or PCM.  
  • Exhaust emits black smoke or smells bad: When the vehicle runs rich, the excess fuel isn’t completely burned during the combustion process. It escapes into the exhaust and results in black smoke or a rotten smell.
  • Carbon buildup on engine components: Incomplete combustion may also result in hardened carbon deposits on engine components like the cylinder walls or intake valves.
  • Illuminated Check Engine Light: If the heating element inside the oxygen sensor heater circuit fails to bring the sensor to an apt operating temperature, it will trigger the Check Engine Light.

Can I still drive?

Yes, you can still drive with a P0135 code. However, it’s a moderately serious issue and is best addressed promptly. 

A functional O2 sensor heater helps maintain efficiency and engine power. So, extended driving with this issue can lead to:

  • Internal engine damage
  • Excessive fuel consumption
  • Increased exhaust emissions

P0135 causes

Here are a few instances that can cause code P0135:

  • A faulty oxygen sensor 
  • High resistance in the O2 heater element
  • An excessive current draw in the heater circuit 
  • A blown heated oxygen sensor fuse
  • Faulty wiring harness or connections
  • A short circuit or open ground in the wiring 
  • A malfunctioning or damaged engine coolant temp sensor
  • Low fuel pressure
  • An air intake system or exhaust system leak
  • A damaged catalytic converter
  • A faulty powertrain control module or engine control module (rare)

Diagnosis

Several issues could trigger engine code P0135 apart from a malfunctioning oxygen sensor heater circuit. This is why it’s important to properly diagnose the code and implement relevant repairs.

Here’s what a mechanic would do to diagnose the problem:

  1. Inspect the electrical connections that lead back to Bank 1 Sensor 1 for fraying, cracked insulation, or other damage.
  2. Inspect the fuse of the heater circuit to see if it’s functional.
  3. Check the wire harness for water entry into the harness connector.
  4. Look for a leak or clog in the exhaust or emission system.
  5. Check the O2 sensor for oil or carbon contamination.
  6. Test the catalytic converter using a vacuum gauge and check the AF sensor in the exhaust manifold to assess air-fuel efficiency.
  7. Scan the code, document freeze frame data, and then clear the codes to verify O2 sensor failure.
  8. Monitor O2 sensor data to check whether the heater circuit is functional.
  9. Test the O2 sensor connector for the proper input voltage and amperage from the PCM/ECM.
  10. Test the resistance of the O2 sensor heater circuit using a multimeter.
  11. Follow other pinpoint tests for the oxygen sensor heater circuit mentioned in the manufacturer’s manual.

Note: This diagnosis helps identify the core of the problem before needlessly replacing any expensive parts, like the O2 sensor. For example, installing a new sensor won’t resolve wiring or harness connector issues.

Possible repairs for P0135 & Costs

Here are the steps your mechanic may take to address code P0135:

  • If they notice any wiring or electrical issues, they will clean and rewire or replace the faulty wiring.
  • They may replace the sensor connector, wire harness, and fuse in the heater circuit.
  • They’ll locate the engine ground and fix corrosion-related issues, adding a replacement ground if needed.
  • They may clean the catalytic converter.
  • If the sensor is faulty, they’ll replace the old sensor with a new O2 sensor. 
  • They’ll conduct a road test to see if the Check Engine Light is still flashing or if the problem is resolved.

Note: The vehicle manual will have a circuit description and wiring diagram of the O2 heater circuit. A mechanic will refer to this guide while replacing the wiring, the heated oxygen sensor connector, and other circuit components.

Code P0135 can have several root causes, from wiring issues, a blown fuse, to a faulty heated oxygen sensor. So, the cost of the repairs depends on the action needed.

Depending on the mechanic’s labor rate, the diagnosis can cost around $75-$150. After the diagnosis, the mechanic will quote the repair cost. 

Here’s a general estimate of the cost of some repairs and replacement parts:

  • Heated Oxygen Sensor Fuse: $5
  • Wiring: $100-$1000
  • Oxygen Sensor: $200-$300 

Note: The repair cost can vary depending on your car’s make and model. And if the Check Engine Light still flashes after the above replacement and fixes, you should consider having the PCM or ECM checked.

How It Works

Tell us about your vehicle

Select your vehicles year, make, and model and the repair service you need.

Book online

Get a free quote, book an appointment, and speak to a specialist – all online!

Schedule your repair

Pick a time that works best for you and our mobile mechanics will bring the shop to you.

Get a Quote

certified 12-Month | 12,000-Mile Warranty

We're here to keep you moving

Our experienced mobile mechanics are ready to help.

Get a Quote

1-Year | 12,000-Mile Warranty