P0135 Fault Code

Long Description

Fault code P0135 is logged when the engine control unit (ECU) has detected an issue with the bank 1 sensor 1 oxygen sensor in the heater circuit.

Bank 1 refers to the side of the engine in which cylinder 1 is located. This can be found in the owner’s manual. Oxygen sensor 1 is the upstream oxygen sensor. The mirror code for bank 2 is P0155.

This error occurs when the ECU detects either an open or short circuit in the heater circuit or an excessive current draw.

This can happen at startup when the ECU tests the upstream heated oxygen sensor.

Audi is one of the most reported manufacturers for this issue. Chevrolet is another brand that suffers this fault code somewhat more regularly than other brands.

Other Signs of This Problem

There are several signs that can give away an issue with a heat oxygen sensor. These typically relate to how the engine runs.

One of the most obvious signs is that the Check Engine light will be illuminated – with an OBD2 reader displaying this P0135 fault code alongside it.

The vehicle may also be running excessively rich. This means there is too much fuel being fed to the combustion chambers at any given time, disrupting the ideal air-fuel ratio.

This can lead to poor fuel economy and carbon buildup on all parts that come into contact with the combustion gases and exhaust fumes.

Additionally, the engine running rich can cause spark plugs to foul out quickly. This can mean the vehicle struggles to start up or misfire due to carbon buildup.

There may also be other heater oxygen sensors logged. Look out for any codes ranging from P0131 all the way up to P0167.

What Could Be The Problem?

The potential causes for fault code P0135 are all electrical in nature. These can range from part malfunctions to improper wiring.

One of the most likely issues is a faulty upstream oxygen sensor. This will obviously provide an incorrect reading that can signal the fault code to be logged.

Additionally, there could be an issue with the wiring or connections. A frayed or damaged wire can disrupt the signal being sent.

This can also happen as a result of an open or short circuit in the wiring.

Fixes

All of the fixes for P0135 are focused on fixing any existing electrical issues. However, it is a good idea to reset the codes and perform a test drive to determine if the code is logged again.

If the oxygen sensor is in fact faulty, it should be replaced.

The wiring and connections between the sensor and the ECU should also be checked for damage or fraying. These should be fixed accordingly. It is also important to ensure that the connections are properly fixed to the components.

The fuse running to bank 1 sensor 2 should also be checked and replaced if need be.

Seriousness

Fault code P0135 should be considered a moderately serious problem. There is no immediate danger to the engine or its components but operating in this state can eventually cause damage.

It can also cause the vehicle to run very poorly after enough carbon buildup is caused. The fuel economy will also be very poor.

It should ideally be fixed as soon as possible.