P0036 Trouble Code definition
P0036 is the code for Heater Oxygen Sensor Control (HO2S) Circuit (Bank 1, Sensor 2)
What the P0036 code mean?
P0036 means that for the engine to operate properly, the engine exhaust should have a specific air fuel ratio of 14.7 to 1 as determined by the heated oxygen sensors (HO2S), which detects the oxygen content of the exhaust.
This sensor data is calculated by the Engine Control Module (ECM) to adjust the correct amount of fuel delivered to the engine. A heater oxygen sensor is heated to make certain of a very high speed response to the ECM closed loop system, which helps decrease emissions during start up and when the engine is in warmup.
What causes the P0036 code?
If the code is cleared and reset, and then the Check Engine Light comes on and the OBD-II code comes back, the HO2S sensor for the engine bank 1 and sensor #2, which is downstream of the catalytic converter, is not sending the proper data to the ECM and may be defective or have defective wiring. It is quite unusual if the ECM has failed.
What are the symptoms of the P0036 code?
With the O2 heater circuit not working, the O2 sensor response time will be affected and the sensor will not respond to fuel and oxygen in the exhaust for the first 3 to 5 minutes of running or more. The lack of response will affect the ECM’s ability to control the fuel mixture and it will go into a fixed fuel mix until the problem is fixed. The Check Engine Light will come on once the failure is detected by the ECM. The ECM will go into failsafe mode causing different drive symptoms depending on manufacture ECM programming.
How does a mechanic diagnose the P0036 code?
P0036 is diagnosed with an OBD-II scanner. The mechanic should reset the OBD-II code and test drive the vehicle to see if the code returns. If it comes back, the mechanic should check both power and ground to the sensor including closely inspecting the wiring and sensor. Many of the problems on this code are wiring related due to the heat of the exhaust damaging other components.
Common mistakes when diagnosing the P0036 code.
Do not assume that you should replace the HO2S before checking the all the related wiring and the connector closely. The mechanic should ensure there is 12 volts to the sensor and the ground is good. He must check both sides of the connector wiring to ensure the connector is good and not damaged.
How serious is the P0036 code?
The P0036 code will usually be preceded by the Check Engine Light coming on the vehicle’s dash while it is in operation. The vehicle can still be driven but it should properly be diagnosed as soon as possible to prevent potential problems like the sensor loop failing, excessive fuel consumption, poor operation, or damage to other components.
Often times, if the Check Engine Light came on immediately at start up, the OBD-II system can be reset and the vehicle will operate normally.
What repairs can fix the P0036 code?
The most common repairs to address the P0036 code are as follows:
Have a certified technician verify the code with a scanner. Reset the fault codes and then perform a road test.
If the P0036 code returns, then follow the test procedure. It can have several problems, but wiring being damaged by excessive heat from the exhaust is most common. Make certain the wiring is in good condition and has proper voltage and ground to the sensor before replacing the sensor.
With key on and the engine off, use a digital voltmeter to check for 12+ volts fused battery feed to the heater element. If there is no voltage present, repair any open or short in the 12 volt feed circuit, but first determine if it is necessary to replace any fuse blown from the short. If the battery feed is correct, remove the ground (control) circuit from the ECM wiring connector and check for resistance on the circuit. If there is infinite resistance, repair the open in the circuit. If the control circuit is good, suspect a bad HO2 sensor. Replace and re-check.
I have found this problem to be a fairly common code that is usually caused by the wiring touching the exhaust system and shorting out the power wire or sensor circuit. Vehicles normally have small wiring clamps on the chassis to hold the wiring away from the exhaust but many are plastic and cannot withstand the heat of the catalytic converter, then fail allowing the wiring to touch the exhaust or worse, the catalytic converter.
If melted, replace the wiring with the correct type of wire, not general electric wiring. Another issue is where a mechanic may have damaged the sensor if it was removed and reinstalled. A common problem can occur when the sensor is removed and damage is done to the female threads on the exhaust, which will require a special tap to repair the threads. But if they are too damaged, a new threaded insert must be welded on the exhaust. Remember these #2 HO2 sensors experience very high heat being at the outlet of the catalytic converter.
Additional comments for consideration regarding the P0036 code.
Many vehicles with mileage over 100,000 have momentary sensor problems that usually occur during start up or prolonged stress situations on the drive train. If the Check Engine Light comes on and the vehicle seems to be operating normally, the OBD-II system can be reset using the scanner and the problem may not reoccur. This is why it is important to verify the fault and reset it before doing any repairs.
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This article originally appeared on YourMechanic.com as P0036 OBD-II Trouble Code: Heater Oxygen Sensor Control (HO2S) Circuit (Bank 1, Sensor 2) and was authored by John Nelson.