Error Code P0036 is defined as a trouble code for Heated Oxygen Sensor (HO2s) Control Circuit, Bank 1, Sensor 2. This can mean that the specified sensor is not sending the right data to the PCM (powertrain control module).

Note that it’s actually a generic definition of the error code. Your vehicle manufacturer may have a different specific and information of the code. GM for example, defines it as ‘Heater Control Circuit Conditions.’


Error Code P0036 means there’s an ongoing problem on the heater element of the HO2S. The job of the control module is to oversee how much time it takes for the sensor to warm up and start sending ample signal. This code is triggered when the sensor is taking too long to warm up.

For the engine to run efficiently, its exhaust should have a specified ratio of air and fuel (14.7:1, respectively) as determined by the HO2S, which works by detecting the oxygen from the exhaust. The data is calculated by the PCM and it adjusts the amount of fuel delivered to the engine automatically. The HO2S is heated to ensure the PCM maintains a high speed response closed loop system, which reduces emissions at startup, and when the engine is still warming up.

This code shows up when the PCM detects that there’s an open or shorted to ground HO2S circuit.

Common Symptoms

Aside from the Check Engine light being activated, symptoms of this error code include symptoms associated with heated circuit failure, as it runs briefly when the vehicle first starts. The same sensor is also after the catalytic converter, thus, will not affect the air/fuel ratio input the PCM receives; it’s usually used to verify the efficiency of the catalytic converter. Other symptoms include:

  • PCM going failsafe mode which results to drivability problems (depending on the PCM programming of the manufacturer)
  • Vehicle failing on emission test

Possible Causes

There can be many causes for this error code. For one, water that enters the HO2S can cause its fuse to blow. Also, the sensor may be defective, or there is defective wiring, keeping the sensor from sending the required data to the PCM. Other possible causes include:

  • Open power, ground wires or open circuit inside the O2 sensor
  • Broken or corroded exhaust system ground strap
  • Failure in the wiring of PCM (or ECM) or O2 sensor heater circuit

How to Check

As with many error codes, Error Code P0036 requires thorough visual checking for loose or damaged wiring to the sensor.

This error code can only be triggered either by the oxygen sensor heater circuit or by the sensor itself. For its diagnosis, it usually starts with the checking of the wiring system of the sensor. Usually, the heated oxygen sensor comes with four wires. Two of the wires head straight to the heater circuit, while the other two are for power and ground of the sensor. This diagnosis is about checking the wires for the heater circuit. You may need a wiring diagram of your vehicle to be sure you’re testing the right set of wires.

Testing the Heater Circuit Wiring

Test the heater circuit wiring using digital multimeter or DVOM (digital volt ohm meter). Again, consult with the vehicle’s wiring diagram for the exact pins of the connector where the ground is set. The other end should touch the power feed, while the other touching the black multimeter lead. The reading must be close to the battery’s voltage. If not, then there’s a good chance your oxygen sensor power supply is the cause of the problem. If so, then you may have to check the power of the vehicle. Check the circuit fault lies from the wiring diagram.

Connect the battery’s positive terminal to the red multimeter lead, and the black lead to the ground to check for the circuit’s ground. The result must be 12V. If not, then you need to refer to the ground side of the wiring diagram.

Testing the Sensor Heating Element

If both power and ground are good, then your next option is to check the sensor heating element to determine whether it’s an open circuit or high resistance. Again, you will need a digital multimeter.

Using the DVOM (digital volt ohm meter) set at Ohm scale, test the heater circuit’s resistance using a wiring diagram as reference. Make sure you unplug the oxygen sensor. The heater circuit inside the sensor must have resistance present. Over limit reading indicates open in the circuit’s heated portion, which indicates replacement for the oxygen sensor.

If the reading says OL, that means there’s an open circuit in the heating element. Again, you need to replace the sensor.

How to Fix

Back-probe the connector’s ground wire and inspect for resistance between the connector to the O2 sensor and the resistance of a good ground.

Then, back probe the wire of the power supply using the DVOM set to DC volts with the negative lead to a good-known ground and the positive to the wire of the power supply to check for supply of the O2 sensor. If you haven’t seen power at the connector during cold start (car startup), then there’s a high chance there’s a problem with the vehicle’s power supply circuit straight to the oxygen circuit of the PCM itself.

Error Code P0036 can be triggered by many different things, but it’s usually damage on the wiring caused by excessive heat that triggers it. Make sure the wiring of the sensor is in good condition, has proper voltage and good ground before replacing the sensor.