Code P0135 - Heated Oxygen Sensor Heater Circuit Malfunction (Bank1 Sensor1)

In some Chrysler vehicles, the code P0135 can be caused by incorrect replacement sensor. Different types of sensor can be used on the same car, depending on the date the car was produced. It's important to verify the correct part number of the sensor by the vehicle VIN number.
Corrosion at the oxygen sensor connector is known to cause this code in many cars. The sensor connector must be inspected for corrosion. If the corrosion is present, the terminals must be cleaned, or the connector must be replaced. For example, the Chrysler TSB for the 2010-2012 Dodge Ram, recommends repairing the sensor wiring harness with a special repair kit. In some older Mazda cars, the corroded wiring inside the fuse box can cause the code P0135. This can be confirmed by checking the 12V power and ground at the sensor.

Example: Diagnosing the code P0135 step by step

Code P0135 diagnostic

The Check engine light came on in this Honda. The code is P0135.

Erasing the DTC with scan tool

According to the service manual for this car, the first step is to clear the code and see if it comes back. This is needed to see if the code is intermittent or always present.

Check Engine light comes back on

We erased the code and started the car. The Check Engine comes back on immediately with the same code.

Fuse description on a fuse box cover

The next step according to the manual for this Honda, is to turn the ignition switch to LOCK position and check the No. 14 FI SUB (15 A) fuse. The location of the fuse is noted on the back of the fuse box cover.

Checking if the fuse is blown

We checked the FI SUB fuse, it's OK. The next step according to the manual is to check the PGM FI subrelay. We tested the relay, it was working too.

Checking resistance of the A/F sensor heating element

The next step in the diagnostic process is to disconnect the A/F sensor connector and measure the resistance of the sensor heater element. The multimeter shows 235 KΩ (Kilo Ohms). According to the service manual, the resistance should be between 2.5 and 4 Ω (Ohm). This means that the A/F sensor heating element has failed, the sensor must be replaced.

Checking resistance of the A/F sensor heating element

We purchased the new A/F sensor and checked the heating element resistance to compare. As you can see, it measures at 2.6 Ω (Ohms). We installed the new sensor and cleared the code. The Check Engine light did not come back, this car is fixed.

What color are the A/F sensor heating element wires? There is no standard color marking. In this Honda the heating element were black, but in some other cars they could be gray, white or another color. It's best to consult the service manual for your car. We posted links to several sites where you can access a service manual for a subscription fee in this page.
How easy is it to replace an A/F sensor? It's not very difficult, but it requires a special oxygen sensor socket. Read more about A/F sensor.

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