Diagnostic Trouble Code P0135

P0135 “O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)”


What is code P0135?

Code P0135 stands for “O2 Sensor Heater Circuit Malfunction”. This diagnostic trouble code can show up when there is a problem with the Pre-catalyst oxygen sensor in your vehicle. Therefore, it is important to have a qualified technician diagnose the specific problem that caused the code to be stored in your vehicle’s computer.

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What does code P0135 mean?

When a technician reads a code P0135 on a diagnostic scan of your vehicle, the information indicates that there is something wrong with the oxygen sensor mounted in the exhaust system upstream of the catalytic converter. The ECM (Engine Control Module) has detected the problem and turned on the check engine light.

Your engine requires that a specific mixture of air and fuel enter the combustion chambers in order for combustion to happen properly. When that air/fuel ratio is out of balance, whether too rich (too much fuel) or too lean (not enough fuel), your engine will not run as it should. Fuel economy also decreases, while harmful emissions from the exhaust system increase.

To help ensure a suitable air/fuel mixture, your vehicle is fitted with anywhere from two to five sensors mounted in the exhaust system that measure the percentage of oxygen present in the exhaust gasses. Data from these oxygen sensors is sent to the ECM where it is analyzed and used to adjust the air/fuel ratio accordingly. If the ECM detects a problem with the electrical signal coming from one of these sensors, it will store a diagnostic trouble code and turn on the check engine light.

Code P0135 refers specifically to the heating element in the oxygen sensor. An oxygen sensor needs to warm up to work effectively. But getting up to operating temperature can take several minutes in some cases. So, a heating element is installed so that the sensor begins warming up as soon as the engine starts. If the ECM detects a problem with the electrical circuit to the sensor’s heater, it will store code P0135 and turn on the check engine light.

What causes code P0135?

A number of causes can trigger a code P0135. That is why an accurate diagnosis is essential. Causes of this code include:

Most likely

  • Faulty oxygen sensor ($200-$500)
  • Damaged or deteriorated wiring to the oxygen sensor
  • Corrosion on the sensor, wiring, or connector

What symptoms are associated with this code?

Common signs associated with a code P0135 include the following:

  • The check engine light is on or flashing
  • Engine idles or runs roughly, especially prior to warm-up
  • Failed emissions test
  • Reduced fuel economy
  • Black smoke from the tailpipe

How does a technician diagnose code P0135?

If a diagnostic scan of your vehicle indicates a code P0130, a technician will perform tests to pinpoint the problem. These tests include checking for any related trouble codes. The technician will also use the scan tool to read the live data from the oxygen sensors and make comparisons under various operating conditions. The wiring that leads to the sensor will also be inspected and tested, along with the sensor heater itself. The technician will also inspect the wiring that leads to the sensor. 

How serious is this code?

In some cases, a code P0135 will not cause any major drivability problems. It is common, however, that the problem will lead to a rough engine idle, hesitation, or stalling as the engine warms up. Fuel economy can suffer as well. At the very least, the presence of the check engine light will prevent your vehicle from passing an emissions test. Code P0135 is not cause for immediate concern, but the vehicle should not be driven excessively. Have it diagnosed within a week or two.

Get this checked out soon by a CarAdvise shop, where the work will be guaranteed, and one of our expert techs will review any repair orders.


Related Diagnostic Trouble Codes

P0130 O2 Sensor Circuit Malfunction

P0131 O2 Sensor Circuit Low Voltage

P0133 O2 Sensor Circuit Slow Response

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